Effect of Ruminal Escape Protein and Fat on Nitrogen Utilization in Lambs Exposed to Elevated Ambient Temperatures' L. D. Buntingz, L. S. Sticker*, and P. J. Wozniakt
ABSTRACT: Eight wether lambs (SI BW = 28.8 kg) with ruminal and abomasal cannulas were assigned to either thermally neutral or high ambient temperature treatments. Within each temperature, lambs were randomly allotted to dietary treatments consisting of a basal diet (60% corn and 24% cottonseed hulls) either with (high; 11.4% CP) or without (control; 10.1% CPI added ruminal escape CP as fish meal and with (high) or without (control15% added ruminally inert fat in a 2 x 2 factorial treatment arrangement using a Latin square design. Lambs were fed 606 g of DM/ d in each period, which consisted of a lo-d adjustment followed by 6 d of sample collection. High temperature increased (P c .05)respiration rate, evaporative water loss, and rectal temperature. When compared with controls, lambs fed high escape CP retained more N when exposed to high temperatures (2.8vs 3.6 g of N/d) and less N
at neutral temperatures (3.3 vs 3.1 g of N/d; temperature x escape CP; P c .05).Retention of N was greater (P c .05)in lambs fed high than in those fed control fat (3.8 vs 2.7 g/d). Lambs fed high vs control escape CP had greater abomasal feed N flow (percentage of intake) when fed highfat diets (77.3vs 56.1%) but similar dietary N flow when fed control fat diets (55.8 vs 54.3%; fat x escape CP; P < .05). Compared with controls, lambs fed high-fat diets had higher (P e .05) ruminal NH3 N concentrations (4.0vs 5.8 mM) and lower ( P e .05) plasma urea N concentrations (5.8 vs 4.5 mM1 and ruminal OM and ADF digestibilities (64.8vs 50.2% and 22.4 vs 5.5%, respectively). Although added fat improved N retention equally at high or neutral temperatures, increased CP, as ruminal escape CP, improved N retention of lambs at high but not at neutral ambient temperatures.
Key Words: Lambs, Heat Stress, Protein, Fat
J. Anim. Sci. 1992. 70:1518-1525
Introduction During thermal stress, dietary CP has been shown to be used with diminishing efficiency as CP levels approach the animal's theoretical requirement (Ames et al., 1980). This is likely attributable, in part, to increased diversion of metabolic energy from growth to thermal regulation (NRC, 1981). However, the proportion of
'Approved by the Director of the Louisiana Agric. Exp. Sta. as publication No. 91-15-5382. 'To whom correspondence should be addressed. Received August 27, 1991. Accepted November 25, 1991.
dietary CP that escapes ruminal degradation (EP) seems to decrease during thermal stress as the probable result of decreased particulate passage rate (Christopherson, 1985). This likely increases ruminal NH3 absorption and energy expenditure attributable to urea synthesis. During periods of thermal stress, it has been observed that diets that are high vs low in escape CP (40to 45 vs 30 to 35% of CP intake) are used more efficiently for milk production in dairy cattle (Higginbotham et al., 1989; Taylor et al., 1991). Fat is a n energy-dense feed component associated with reduced metabolic heat production per unit of energy fed (Baldwin et al., 19801, and its inclusion in the diets of thermally stressed ruminants should represent a plausible method for reducing metabolic heat production. Because all
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Departments of *Dairy Science and +Experimental Statistics, Louisiana State University Agricultural Center, Louisiana Agricultural Experiment Station, Baton Rouge 70803
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ESCAPE PROTEIN AND FAT FOR LAMBS
Table 1. Ingredient composition and chemical analysis of diets (DM basis) Treatments Control fat Item
High fat
High EP
59.50 24.00 5.00 8.30 .55 .55 .65
59.50 24.00 5.00 5.05 5.50 .IO .40 .45 -
59.50 24.00 5.00 3.30 5.00 .55 .55 .05
+
+
+
+
10.2 63.8 29.9 34.0 21.4
11.2 83.0 39.7 44.0 28.6
10.0 05.7 30.7 35.0 21.7
11.7 81.1 38.5 42.6 18.0
Ingredient composition Ground corn Cottonseed hulls Soybean meal Rice hulls Ruminally protected fat Fish meal Fish oil Urea Limestone Dicalcium phosphate Trace mineral saltb Sodium sulfate Vitamin premixC Chemical analysis CP Total amino acids W, Ya of CP Essential fL4. oh of CP Nonessential AA, Oh of CP
ADF
.90
.45 .10
Control EP
.90
.45 .10
High EP 59.50 24.00 5.OO .05 5.OO 5.50 .10 .40 .45 -
aEP = ruminal escape protein. bTrace mineral salt provided the following per kilogram of diet: NaCl, 4.4 g; Mn, 14 mg; Fe, 8.5 mg; Cu, 2.3 mg; I. .23 mg; and Co, .24 mg. CVitaminpremix provided the following per kilogram of diet: vitamin A, 1,800IU; vitamin D,190 IU.
energy in feed fat, except for component glycerol, is utilized postruminally, increasing dietary fat should increase the requirement for high-quality escape CP. The following study was conducted to determine the effect of increased dietary fat and escape CP levels on apparent metabolic heat load and N utilization in thermally stressed lambs under conditions of controlled DMI.
Experimental Procedures Eight unshorn (approximately 2 cm of fleece depth) Suffolk wether lambs were equipped with plastic cannulas (1.3 cm i.d.1 in the dorsal sac of the rumen and approximately 12 cm from the pyloric sphincter in the abomasum (Komarek, 1981). After a 2-mo recovery period, lambs (57 initial BW = 28.8 kg) were allotted to either thermally neutral or high ambient temperature treatments (four lambs per treatment) such that body size was similar between the treatment groups. Within each ambient temperature treatment, lambs were randomly assigned to the four dietary treatments using a Latin square design. The study was conducted during the months of August, September, and October 1989; lambs on the high temperature treatments were kept in a n enclosed, ventilated room exposed to normal daily temperature
variation for the duration of the study. During cooler weather in October, a portable electric heater was used to maintain elevated room temperature. In the high-temperature room, daily maximum and minimum temperature averaged 30 f 3 and 24 f 2"C, respectively, and relative humidity averaged 79.1%. Lambs exposed to neutral temperature were kept in an air-conditioned room (21 k l"C1 throughout the study. All lambs were housed in individual wooden metabolism stalls with continuous illumination throughout the experiment. Dietary treatments consisted of either a control or high level of escape CP either with (high) or without (control) 5 %O of a sodium-alginate-encapsulated dry tallow (Booster Fat, Balanced Energy, Clinton, IA; Table 1). The control and high escape CP diets were formulated to meet approximately 90 and loo%, respectively, of the CP requirement and 100% of the requirements for energy, minerals, and vitamins for lambs (NRC, 19851, using maximum DMI assumptions that considered the effects of heat stress and restraint in stalls. Diets were also formulated to contain similar levels of ruminal fermentable energy and degradable CP. Fish meal was included in the high escape CP diets such that a ratio of approximately 70 g of escape CP per megacalorie of fat-derived ME would be maintained on the high escape CP-high fat diet.
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Control EPa
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with HC1 for 22 h at 110°C (Spitz, 1973). Cystine, methionine, and tryptophan were not included in computations of total essential amino acids due to variable destruction of these amino acids during acid hydrolysis. Abomasal contents and bacterial pellets were analyzed for purines by the procedure of Zinn and Owens (1986) as modified by Ushida et al. (1985). Bacterial N and amino acids in abomasal contents were computed using the purine N:total N or amino acid ratios in isolated bacteria. Quantities of nutrients digested in the rumen were calculated by reference to Cr ratios in feed and abomasal contents. Statistical analyses were conducted using the GLM procedure of SAS (1985). A split-plot design was employed with temperature as the whole plot and escape CP and fat levels as the subplot. The effect of temperature was tested using animal within temperature level as the whole-plot error. Period was used as a blocking variable on the subplot, and the subplot analysis took into account the treatment restrictions of a Latin square design for a given temperature. The effects of period, fat, escape CP, fat x escape CP, and the interaction of each of these with temperature were tested using residual error as the subplot error term.
Results and Discussion Throughout the adjustment and collection periods, lambs kept at neutral temperature consumed their entire 12-hmeal within 1 to 2 h after feeding. Lambs kept at high temperature consumed approximately 80% of their meal within 2 h but, generally, required the entire 12-h feeding cycle to complete the meal. Ruminal insertion of refused feed was occasionally required for lambs kept at high temperature during extremely hot weather; however, feed administered in this manner represented less than 2 % of total DMI. Daily DMI averaged 606 g per lamb and represented a n average of 2.1% of BW. The marginal increases ( P e .05) in rectal temperature with elevated temperature suggest that the lambs were able to dissipate most of their excess heat load through panting, which is the principal mode of heat dissipation in thermally stressed ruminants (Table 2; NRC, 1981). Mean respiration rate was twofold greater ( P e .05) for lambs kept at high than for those kept at neutral temperatures. Lambs kept at high temperatures and those kept at neutral temperatures consumed similar ( P > .05) amounts of water. Elevated temperature increased (P e .05)evaporative water loss, computed as the difference between water intake and urine volume, but did not affect ( P >
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Each 16-d treatment period consisted of a 10-d dietary adjustment followed by 6 d of collection of excreta and digestive contents. During the final 5 d of the adjustment period and throughout the collection period, .45 g of chromic oxide was administered through the ruminal cannula at each feeding. Intake of all lambs was restricted to approximately 90% of that which was voluntarily consumed by lambs kept at high temperature. Feed was offered in equal portions at 12-h intervals. During the final 4 d of the adjustment period and throughout the collection period, feed not voluntarily consumed within a 12-h feeding cycle was manually inserted into the rumen through the ruminal cannula a t the subsequent feeding. Lambs were allowed unlimited access to water from plastic troughs. During the collection period, water refusals were weighed, and fresh water was provided a t each feeding. During the collection period, rectal temperature and respiration rate were recorded on d 1 at 2000, d 3 at 1600, and d 5 at 1200. Respiration rate was measured by the same person throughout the experiment and was recorded as the average time required for the lamb to complete 20 breaths. Immediately after these measurements, blood samples (10 mL) were collected into evacuated, heparinized tubes by jugular puncture. Daily fecal collections were dried for 7 d a t 50" C in a forced-air oven. Urine was collected into plastic vessels containing sufficient 6 N HC1 to maintain pH below 2.0 and an aliquot was retained each day and frozen. Daily feces and urine collections were pooled to yield individual lamb composites for chemical analyses. Also beginning on d 1, samples of ruminal fluid (50 mL) and abomasal contents (100 mL) were collected at 12-h intervals advanced 2 h daily for 6 d and frozen. Samples of abomasal contents were lyophilized and pooled on an equal-weight basis into individual lamb composites. Ruminal fluid samples were thawed and pooled on a n equal-volume basis into individual lamb composites. Ruminal fluid composites were centrifuged a t 1,000 x g for 15 min, and the resulting supernatant was centrifuged at 20,000 x g for 15 min, to obtain a bacteria-rich pellet. Pellets isolated from these ruminal fluid composites were used to determine purine N:total N ratios. Blood samples were centrifuged at 2,000 x g for 15 min, and plasma was retained for analysis. When appropriate, feed, excreta, bacterial pellets, and abomasal contents were analyzed for N (AOAC, 19841, ADF (Goering and Van Soest, 19701, and Cr (Kimura and Miller, 19571. Ruminal NH3 N and plasma urea N were determined as described previously (Sticker et al., 1991). Amino acids in abomasal contents were separated on a Beckman Model 6300 amino acid analyzer after hydrolysis
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ESCAPE PROTEIN AND FAT FOR LAMBS
Table 2. Physiological responses of lambs fed various levels of fat and ruminal escape protein (EP) at thermoneutral or high ambient temperatures
Item Respiration rat e, breathdmin Rectal temperature, "C Water intake, L/d Evaporative water loss, L/d
Ambient temperature
Fat level
EP level
Neutral High
Control High
Control High
50.7 39.5 3.3 1.o
105.3 39.8 3.7 1.7
75.8 39.6 4.0 1.2
80.2 39.7 3.0 1.5
70.1 39.6 3.4 1.3
79.9 39.6 3.6 1.5
.05)urine volume (data not shown). By comparison, Bhattacharya and Hussain (1974) reported threefold increases in respiration rates of Awasi wethers when subjected to similar environmental regimens. Although water intake was increased, rectal temperature was not influenced by elevated temperature in their study. At neutral temperature, diet did not influence respiration rates or rectal temperatures. Conversely, during high temperature, respiration rates and rectal temperatures were higher for lambs fed high than for those fed control escape CP when fed a high level of fat (128 vs 92.3 breathdmin and 39.9 vs 39.8"C, respectively) but lower when fed a low level of fat (93.4 vs 107.4 breathslmin and 39.7 and 39.9" C, respectively; temperature x fat x escape CP level interaction; P < .05).In addition, fat x escape CP level and temperature x escape CP level interactions ( P < .05)were observed for respiration rate. Moreover, water intake was lower (P < .05) for lambs fed high than for those fed control fat diets. The physiological significance of these dietary effects is not certain. Ruminal digestion of OM and ADF and total tract digestion of ADF were not affected (P > .05) by temperature or escape CP level [Table 3). The fiber digestibilities observed in this study are somewhat low but are consistent with those often reported when cottonseed hulls are fed in grainbased diets (Bunting et al., 1984; Kinser et al., 1988). Increased digestibility of DM and ADF is often reported for animals exposed to high temperature (NRC, 198 11. Enhanced nutrient digestibility has been attributed primarily to a reduction in the rate of feed passage through the digestive tract incident to heat-induced reductions in DMI and, potentially, decreased gut motility and rumination (NRC, 1981). Intake-induced effects on feed passage rate were eliminated in our study, because DMI was held constant. Moreover, most factors affecting digestion likely become less significant when diets of high potential digestibility, such as those used in our study, are fed (Beede and Collier, 1986).
Effectsa
4.4 T, .05 T, .42 F .22 T (P
.05)by temperature [Table 31, suggesting that the magnitudes of any potential changes in particulate passage incident to thermal stress were not sufficiently great to alter the escape of feed N from the rumen. Lambs fed the high escape CP diets had more (P < .05)total and dietary N reaching the abomasum and had a greater (P < .05) percentage of total N flow composed of dietary N than lambs fed control diets. High dietary fat also seemed to have decreased ruminal CP degradation, because lambs fed high-fat diets had a greater (P < .05)amount and percentage of total N and a greater (P < .05)amount and percentage of dietary N reaching the abomasum than did lambs fed the control fat diet (Table 3). As a consequence, dietary N flow was greater and composed a greater percentage of total N flow in lambs fed high escape CP than in controls when fed with a
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T ' = temperature effect (P c ,051,F = fat level effect (P < ,051,F x P = fat x EP interaction interaction (P < ,051,and T x F x P = temperature x fat x EP interaction (P < ,051.
SE
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BUNTING ET AL.
Table 3. Daily intake, digestion, abomasal N flow, N excretion and retention, and plasma and ruminal N metabolites in lambs fed various levels of fat and ruminal escape protein (EP) at thermoneutral or high ambient temperatures Ambient temperature Item OM intake, g/d N intake, g/d Apparent digestion, YO of intake OM in rumen” ADF in rumen ADF in total tract Total abomasal N flow, g/d oh of intake Bacterial N flow, g/d Dietary N flow, g/d Oh of intake Bacterial efficiency, g of CP/100 g of apparently fermented OM N excreted, g/d Fecal Urinary N absorbed, g/d N retained, g/d O/O of intake YO of absorbed Ruminal NH3 N. mM Plasma urea N, mM
EP level
Fat level
Neutral
High
Control
High
Control
High
579.0 10.5
579.0 10.4
578.9 10.4
579.2 10.5
578.0 9.8
580.1 11.1
58.6 13.9 34.5 9.1 86.8 3.6 5.5 52.0
56.5 13.9 31.3 9.7 92.8 3.6 6.1 57.9
64.8 22.2 34.0 8.9 85.6 4.O 4.9 47.3
50.2 5.5 31.8 9.9 94.1 3.2 6.6 62.6
58.9 18.5 34.0 8.7 89.3 3.9 4.8 49.5
56.1 9.3 31.9 10.0 90.4 3.3 6.7 60.4
4.1 10.9 2.6 .44 4.1 .44 .55 5.4
F F
6.9
7.3
6.8
7.3
7.6
6.6
1.2
F
3.0 4.2 7.4 3.2 30.7 43.5 4.7 5.5
3.2 4.0 7.2 3.2 30.7 44.2 5.1 4.8
3.0 4.7 7.4 2.7 25.6 36.2 4.0 5.8
3.2 3.5 7.2 3.8 35.8 51.4 5.8 4.5
3.1 3.6 6.7 3.0 31.2 45.6 5.1 4.7
3.2 4.6 7.9 3.4 30.2 42.1 4.7 5.6
.23 .21 .21 .25 2.3 3.0 .98 .56
-
aP = EP effect (P < .051,F = fat level effect (P < ,051,F interaction (P < ,051. bCorrected for contribution of bacterial OM.
x
P
=
fat
x
EP interaction ( P < ,051,and T
SE -
-
x
Effectsa -
-
F, P F F, F x P F, P, F x P F, P, F x P x
P
F, P,T x P P F, T x P F, T x P F, T x P F F, P
P = temperature
x
EP
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somewhat low compared with a range of microbial efficiency values reported across a number of studies with cattle and sheep (Stern and Hoover, 1979). Because this likely results from the restricted DMI used in our study, the applicability of these efficiency values to similar diets at maximum DMI seems somewhat dubious. Fecal N excretion was not affected (P > .lo) by treatment (Table 3). Hence, the digestible fiber that apparently escaped ruminal fermentation in lambs fed high-fat diets did not seem to result in significant synthesis of microbial N in the large intestine through its compensatory fermentation in that organ. Compared with controls, lambs fed high-fat diets excreted less (P c .05) urinary N, retained more (P e .05) N, and retained a greater (P e .05) percentage of N both consumed and absorbed (Table 31. Glenn et al. (1977) observed a response of similar magnitude in lambs kept a t neutral temperature fed 5 to 6 % added fat as tallow or vegetable oil, when linseed meal protein was precoated with fat sources. Given its high energy density and low heat increment of feeding (Baldwin et al., 19801, fat should represent a plausible method for reducing metabolic heat production during periods of thermal stress. Skaar et al. (1989) reported increased
high-fat diet (8.2 vs 5.1 g N/d and 77.3 vs 56.1°/o, respectively), but both variables were similar to controls when fed without added fat (5.3 vs 4.6 g N/d and 55.8 vs 54.30/0, respectively; fat x escape CP interaction; P < .05).This suggests that the presence of high dietary fat was the primary determinant of the proportion of dietary N escaping the rumen. Because the proportion of dietary N escaping ruminal degradation was similar for the high escape CP and control diets when fed without added fat, the greater amount of dietary N reaching the abomasum of lambs fed the high escape CP diet seemed to be attributable primarily to the higher N content of this diet. Decreased ruminal OM fermentation resulted in reduced (P c .05) synthesis of bacterial N in lambs fed the high vs control fat diet (Table 3). As a result of the apparent interaction between ruminal energy level and CP solubility, bacterial N flow and efficiency of CP synthesis were lower for lambs fed high than for those fed control escape CP when fed with a high-fat diet (2.4vs 4.0 g of N/d and 5.9 vs 8.8 g of CP/lOO g of fermented OM, respectively) but greater when fed without added fat (4.2vs 3.7 g of N/d and 7.2 vs 6.5 g of CP/lOO g of fermented OM, respectively; fat x escape CP interaction; P c .051. These bacterial efficiency values seemed to be
ESCAPE PROTEIN AND FAT FOR LAMBS
There is evidence that a greater proportion of ruminal escape CP is required for a given level of performance under conditions of thermal stress than during thermal neutrality (Higginbotham et al., 1989; Taylor et al., 19911. It has been suggested that the proportion of dietary CP that is ruminally degraded increases during heat stress, as a result of decreased particulate passage rate (Christopherson, 1985). This would likely increase the production and subsequent absorption of NH3 N from the rumen, with corresponding increases in the synthesis and excretion of urea N. High-CP diets containing moderately low proportions of escape CP have been reported to be more detrimental to the lactation performance of thermally stressed dairy cattle than similar diets containing greater proportions of escape CP (Higginbotham et al., 19891. Because a constant CP: energy ratio was maintained in our study, the effects of proportion of escape CP were confounded with the percentage of total CP in the diet. Furthermore, with no demonstrated effect of temperature on ruminal CP degradability, it must be concluded that thermal stress increased the lamb's requirement for CP ke., amino acids) beyond that which could be supplied by the control escape CP diet at the level of DMI established in this experiment. This may indicate that thermal stress decreases the available amino acid pool for growth through increased protein turnover or increases the protein requirement for specific maintenance functions related to thermal stress. Ruminal NH3 N concentrations were similar ( P > .05) for lambs fed high vs control levels of escape CP but were higher (P e .05) for lambs fed high than for those fed control levels of fat. In spite of higher ruminal NH3 N concentrations, plasma urea N concentrations were lower (P < .05) for lambs fed high than for those fed control fat. This likely reflected the higher rates of N accretion observed for these lambs. Plasma urea N concentrations were higher (P e .051for lambs fed high than control levels of escape CP (Table 3). Amino acid profiles of isolated ruminal bacteria were essentially identical across diets (Table 4) and were quite similar to previously reported amino acid profiles of ruminal bacteria (Bergen et al., 1968). Accordingly, the dietary contributions to abomasal amino acid flow were estimated by subtracting the bacterial contribution to the passage of each amino acid. Patterns of amino acids flowing to the abomasum paralleled that observed for N and seemed to reflect dietary differences in amino acid content, suggesting relative uniformity in ruminal degradation of dietary amino acids. High levels of either fat or escape CP increased ( P e .05) both the total flow and that of dietary origin
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milk yields in cows fed 5 OO/ supplemental ruminally inert fat under moderately warm conditions (late spring and summer; 23°C daily average) but no response to supplemental fat in the winter. In contrast, Moody et al. (1967) exposed lactating cows to cool (15 to 24°C) outdoor conditions or chamber-controlled thermal stress (constant 32"C) while feeding diets containing 0 to 10% of either hydrogenated vegetable fat or soybean oil. Fat and temperature had independent effects on e n ergy-corrected milk yield, which was only marginally influenced by added lipid. However, the ruminal effects of such a high level of fat and disturbances in protein:energy ratio were not controlled in their study. Knapp and Grummer (199 1) similarly observed independent diet and temperature effects when lactating cows were exposed to thermal neutrality (constant 21"CI or chamber-controlled thermal stress (32"C 14 h/d and 26°C 10 h/d) either with or without 5 % of a mixture of ruminally protected fat and tallow. Similarly, results of the present study suggest that supplemental fat is equally beneficial under n e u tral or thermal stress conditions. Temperature did not affect (P e .051 the amount or efficiency of N retention by lambs. During thermal stress, dietary CP has been shown to be used with diminishing efficiency as dietary CP concentrations approach the animal's theoretical requirement (Ames et al., 1980). This is thought to be attributable to increased diversion of metabolic energy from growth to thermal regulation (NRC, 19811, resulting in a lower effective CP requirement to maintain a n optimal protein:energy ratio. Although they absorbed more ( P c .051 N, lambs fed high escape CP excreted more (P e .051 urinary N and, consequently, retained an amount of N similar ( P > .051 to the amount retained by controls (Table 3). However, lambs fed high escape CP excreted marginally more urinary N than controls at high temperature (4.2 vs 3.7 g of N/d, respectively) but substantially more N than controls a t neutral temperature (4.9 vs 3.5 g of N/d, respectively; temperature x escape CP interaction; P .: .05). As a result, compared with controls, lambs fed high escape CP retained more N when exposed to high temperature (2.8 vs 3.6 g of N/d, respectively) but less N at neutral temperature (3.3 vs 3.1 g of N/d, respectively; temperature x escape CP interaction; P .: .05). Similarly, lambs fed high escape CP retained a marginally greater percentage of both N intake and N absorbed than controls at high temperature (32.5 vs 29.0% and 45.2 vs 43.2010, respectively; temperature x escape CP interaction; P .: .05) but smaller percentages a t neutral temperature (28.0 vs 33.4% and 39.0 vs 47.9%, respectively; temperature x escape CP interaction; P e .05).
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BUNTING ET AL.
1524
greater for lambs fed high than for those fed control escape CP, respectively. Methionine, lysine, and threonine have been reported to be the limiting amino acids in microbial protein (Nimrick et al., 1970; Richardson and Hatfield, 1978). Given the amino acid flow observed in the present study, it does not seem likely that protein quality would have been a significant limiter of lamb growth responses.
Implications The results of this study suggest that supplemental fat is equally beneficial for N retention under thermally neutral or thermal stress conditions. Hence, management decisions on whether to include supplemental fat in the diets of thermally stressed ruminants should be based strictly on the cost-effectiveness of maintaining animal perform-
Table 4. Amino acid (AA) flow to the abomasum of lambs fed various levels of fat and ruminal escape protein (EP) at thermoneutral or high ambient temperatures Ambient temperature Item
Neutral
Total AA flow, g/d Total nonessential Total essential Arginine Histidine Isoleucine Leucine Lysine Phenylalanine Threonine Valine Dietary AA flow, g/d Total nonessential Total essential Arginine Histidine Isoleucine Leucine Lysine Phenylalanine Threonine Valine Dietary AA flow, oh of intake Total nonessential Total essential Arginine Histidine Isoleucine Leucine Lysine Phenylalanine Threonine Valine
&P = EP effect (P < ,051,F interaction (P c ,051.
34.2 17.3 16.9 1 .9 .98 1.8 3.8 2.3 1.9 1.8 2.1 17.4 9.1 8.3 .91
.BO .79 2.1 1.2 .92 .80 1 .o 40.8 40.3 41.3 31.5 42.2 42.7 43.4 46.7 39.5 40.3 43.2 =
Fat level
High 36.8 18.6 18.2 2.0 1.1 2.0 4.1 2.3 2.1 1.9 2.2 19.8 10.3 9.5 1.0 .68
.91 2.4 1.4 1.1 .90 1.2 46.6 45.8 47.5 35.7 48.1 49.7 50.4 53.4 45.5 46.1 50.4
Control
High
33.2 16.8 16.4 1.8 .95 1.8 3.6 2.3 1.9 1.8 2.0 14.4 7.6 6.8 .74 .53 .62 1.8 .95 .74 .62 .83 34.7 34.6 34.9 26.6 37.8 35.1 37.8 39.4 32.7 32.8 37.0
fat level effect P < ,051,F
x
P
=
EP level
37.8 19.2 18.6 2.1 1.1 2.0 4.2 2.4 2.1 2.0 2.3 22.8 11.8 11.0 1.2 .75 1.1 2.7 1.6 1.2 1.1 1.3 52.6 51.5 53.8 40.7 52.5 57.3 56.0 60.7 52.3 53.7 56.7
fat
x
Control
High
32.9 16.7 16.2 1 .e .94 1.8 3.7 2.1 1 .9 1.7 2.0 14.7 7.7 7.0 .70 .53 .66
1.9 .92 .80 .62 .85 42.4 41.8 43.1 30.8 44.9 44.9 46.3 50.6 40.8 40.6 45.2
EP interaction
(P c
SE
Effectsa
38.1 19.3 18.8 2.1 1.1 2.0 4.1 2.6 2.1 2.0 2.3 22.5 11.7 10.9 1.2 .75 1 .o 2.6 1.6 1.2 1.1 1.3 44.9 44.3 45.6 36.5 45.4 47.5 47.5 49.5 44.1 45.9 48.4
1.6 .85 .75 .09 .04 .08 .18 .13 .09 .08 .09 2.5 1.2 1.3 .15 .06 .16 .26 .22 .l6 .15 .16 6.9 6.4 2.5 6.1 4.7 10.3 6.0 11.6
,051,and
T
F, P F, P F, P F. P, T x F. P,T x F, P F, P P, F x P, F, P F. P F. P F, P, F x F, P, F x F, P, F x F, P, F x F, P, F x F, P, F, P, F, P, F, P, F, P, F, P,
F F F
x
F F
x
F
F, F F, F F, F F, F F, F F, F F, F F
x
7.6
F, F
9.2 7.8
F, F F, F
x x
x
F
=
x x x x x x
x
x x x x
F F T
F
x
P P P P P P P P P P P
P P P P P P P P P P
temperature
x
fat
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for total amino acids and total essential and nonessential amino acids. Flow of dietary total and total essential and nonessential amino acids as a percentage of amino acid intake was greater ( P e .05)for lambs consuming high than for those consuming control levels of fat. In addition, both the amount and percentage of amino acid intake of total and total essential and nonessential amino acids of dietary origin flowing to the abomasum were greater in lambs fed high escape CP than in controls when fed with high fat but were similar to controls when fed without added fat (fat x escape CP interaction; P < .05).The total quantities of either total essential or total nonessential amino acids reaching the abomasum were 16% greater for lambs fed high than for those fed control escape CP. Although flow of other individual essential amino acids was near to or less than this magnitude, the total amount of lysine and threonine reaching the abomasum was 24 and 18%
ESCAPE PROTEIN AND FAT FOR LAMBS
Literature Cited Ames, D. R., D. R. Brink, and C. L. Willms. 1980. Adjusting protein in feedlot diets during thermal stress. J. h i m . Sci. 50:l.
AOAC. 1984.Official Methods of Analysis (14th Ed.]. Association of Official Analytical Chemists, Arlington, VA. Baldwin, R. L., N. E. Smith, J. Taylor, and M. Sharp. 1980. Manipulating metabolic parameters to improve growth rate and milk secretion. J. h i m . Sci. 51:1416. Beede, D. K., and R. J. Collier. 1986.Potential nutritional strategies for intensively managed cattle during thermal stress. J. Anim. Sci. 62:543. Bergen, W. G., D. B. Purser, and J. H. Cline. 1968. Effect of ration on the nutritive quality of rumen microbial protein. J. Anim. Sci. 27:1497. Bhattacharya, A. N., and F. Hussain. 1974. Intake and utilization of nutrients in sheep fed different levels of roughage under heat stress. J. Anim. Sci. 38:877. Bunting, L. D., C. R. Richardson, and R. W. Tock. 1984.Digestibility of ozone-treated sorghum stover by ruminants. J. Agric. Sci. (Camb.) 102:747. Christopherson, R. J. 1985. The thermal environment and the ruminant digestive system. In: M. K. Yousef (Ed.) Stress Physiology in Livestock. Vol. 1. Basic Principles. pp 183-180. CRC Press, Boca Raton, FL. Glenn, B. P., D. G. Ely, and J. A. Boling. 1977. Nitrogen metabolism in lambs fed lipid-coated protein. J. A n h . Sci. 46:871. Goering, H. K., and P. J. Van Soest. 1970.Forage fiber analyses (Apparatus, reagents, procedures, and some applications). Agric. Handbook 379. ABS, USDA, Washington, DC. Higginbotham, G. E., M. Torabi, and J. T. Huber. 1989.Influence of dietary protein concentration and degradability on performance of lactating cows during hot environmental temperatures. J. Dairy Sci. 72:2554. Kimura, F. T., and V. L. Miller. 1957.Improved determination of chromic oxide in cow feed and feces. J. Agric. Food Chem. 5:216.
Kinser, A. R., G.C. Fahey, Jr., L. L. Berger, and N. R.Merchen. 1988. Low-quality roughages in high-concentrate pelleted diets for sheep: Digestion and metabolism of nitrogen and energy as affected by dietary fiber concentration. J. Anim. sci. 66:487. Knapp, D. M., and R. R. Grummer. 1991. Response of lactating dairy cows to fat supplementation during heat stress. J. Dairy Sci. 74:2573. Komarek, R. J. 1981.Rumen and abomasal cannulation of sheep with specially designed cannulas and a cannula insertion instrument. J. Anim. Sci. 53790. Moody, E. G.,P. J. Van Soest, R. E. McDowell, and G. L. Ford. 1967.Effect of high temperature and dietary fat on performance of lactating cows. J. Dairy Sci. 50:1909. Nimrick, K. E, E. E. Hatfield, J. Kaminski, and F. N. Owens. 1970.Quantitative assessment of supplemental amino acid needs for growing lambs fed urea as the sole nitrogen source. J. Nutr. 100:1293. NRC. 1981. Effect of Environment on Nutrient Requirements of Domestic Animals. National Academy Press, Washington, DC. NRC. 1 Q85.Nutrient Requirements of Sheep. National Academy Press, Washington, DC. Palmquist, D. L. 1984. Use of fats in diets for lactating dairy cows. In: J. Wiseman (Ed.) Fats in Animal Nutrition. pp 357-381. Butterworths, London. Richardson, C. R.. and E. E. Hatfield. 1978.The limiting amino acids in growing cattle. J. Anim. Sci. 46:740. SAS. 1985. SAS User’s Guide: Basics. SAS Inst. Inc., Cary, NC. Skaar, T. C., R. R. Gnunmer, M. R. Dentine, and R. H. Stauffacher. 1989.Seasonal effects of prepartum and postpartum fat and niacin feeding on lactation performance and lipid metabolism. J. Dairy Sci. 72:2028. Spitz, H. D. 1973. A new approach for sample preparation of protein hydrolyzates for amino acid analysis. Anal. Biochem. 56:66. Stem, M. D., and W. H. Hoover. 1979. Methods for determining and factors affecting rumen microbial protein synthesis: A review. J. Anim. Sci. 49:1590. Sticker, L. S.,L. D. Bunting, W. E. Wyatt, and G. W. Wolfrom. 1991. Effect of supplemental lysocellin and tetronasin on growth, ruminal and blood metabolites, and ruminal proteolytic activity in steers grazing ryegrass. J. Anim. Sci. 6s: 4273.
Taylor, R. B.,J. T. Huber, R. A. Gomez-Alarcon, F. Wiersma, and X. Pang. 1991. Influence of protein degradability and evaporative cooling on performance of dairy cows during hot environmental temperatures. J. Dairy Sci. 74:243. Ushida, K., L. Bernadette, and J.-P. Jouany. 1985.Determination of assay parameters for RNA analysis in bacterial and duodenal samples by spectrophotometry. Influence of sample treatment and preservation. Reprod Nutr. Dev. 25:1037. Zinn, R. A., and F. N. Owens. 1986.A rapid procedure for purine measurement and its use for estimating net ruminal protein synthesis. Can. J. Anim. Sci. 66:157.
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ance through increased dietary energy density when heat-induced decreases in dry matter intake occur. These data further suggest that, at restricted dry matter intake, diets of thermally stressed, growing ruminants should be formulated to contain a higher level of crude protein (CPI by means of an increased amount and proportion of escape CP. However, diet fermentability, amino acid content and intestinal availability of escape CP, and level of animal performance will ultimately determine the optimum dietary CP concentration and proportion of escape CP.
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ABSTRACT: Eight wether lambs (SI BW = 28.8 kg) with ruminal and abomasal cannulas were assigned to either thermally neutral or high ambient temperature treatments. Within each temperature, lambs were randomly allotted to dietary treatments consisting of a basal diet (60% corn and 24% cottonseed hulls) either with (high; 11.4% CP) or without (control; 10.1% CPI added ruminal escape CP as fish meal and with (high) or without (control15% added ruminally inert fat in a 2 x 2 factorial treatment arrangement using a Latin square design. Lambs were fed 606 g of DM/ d in each period, which consisted of a lo-d adjustment followed by 6 d of sample collection. High temperature increased (P c .05)respiration rate, evaporative water loss, and rectal temperature. When compared with controls, lambs fed high escape CP retained more N when exposed to high temperatures (2.8vs 3.6 g of N/d) and less N
at neutral temperatures (3.3 vs 3.1 g of N/d; temperature x escape CP; P c .05).Retention of N was greater (P c .05)in lambs fed high than in those fed control fat (3.8 vs 2.7 g/d). Lambs fed high vs control escape CP had greater abomasal feed N flow (percentage of intake) when fed highfat diets (77.3vs 56.1%) but similar dietary N flow when fed control fat diets (55.8 vs 54.3%; fat x escape CP; P < .05). Compared with controls, lambs fed high-fat diets had higher (P e .05) ruminal NH3 N concentrations (4.0vs 5.8 mM) and lower ( P e .05) plasma urea N concentrations (5.8 vs 4.5 mM1 and ruminal OM and ADF digestibilities (64.8vs 50.2% and 22.4 vs 5.5%, respectively). Although added fat improved N retention equally at high or neutral temperatures, increased CP, as ruminal escape CP, improved N retention of lambs at high but not at neutral ambient temperatures.
Key Words: Lambs, Heat Stress, Protein, Fat
J. Anim. Sci. 1992. 70:1518-1525
Introduction During thermal stress, dietary CP has been shown to be used with diminishing efficiency as CP levels approach the animal's theoretical requirement (Ames et al., 1980). This is likely attributable, in part, to increased diversion of metabolic energy from growth to thermal regulation (NRC, 1981). However, the proportion of
'Approved by the Director of the Louisiana Agric. Exp. Sta. as publication No. 91-15-5382. 'To whom correspondence should be addressed. Received August 27, 1991. Accepted November 25, 1991.
dietary CP that escapes ruminal degradation (EP) seems to decrease during thermal stress as the probable result of decreased particulate passage rate (Christopherson, 1985). This likely increases ruminal NH3 absorption and energy expenditure attributable to urea synthesis. During periods of thermal stress, it has been observed that diets that are high vs low in escape CP (40to 45 vs 30 to 35% of CP intake) are used more efficiently for milk production in dairy cattle (Higginbotham et al., 1989; Taylor et al., 1991). Fat is a n energy-dense feed component associated with reduced metabolic heat production per unit of energy fed (Baldwin et al., 19801, and its inclusion in the diets of thermally stressed ruminants should represent a plausible method for reducing metabolic heat production. Because all
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Departments of *Dairy Science and +Experimental Statistics, Louisiana State University Agricultural Center, Louisiana Agricultural Experiment Station, Baton Rouge 70803
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ESCAPE PROTEIN AND FAT FOR LAMBS
Table 1. Ingredient composition and chemical analysis of diets (DM basis) Treatments Control fat Item
High fat
High EP
59.50 24.00 5.00 8.30 .55 .55 .65
59.50 24.00 5.00 5.05 5.50 .IO .40 .45 -
59.50 24.00 5.00 3.30 5.00 .55 .55 .05
+
+
+
+
10.2 63.8 29.9 34.0 21.4
11.2 83.0 39.7 44.0 28.6
10.0 05.7 30.7 35.0 21.7
11.7 81.1 38.5 42.6 18.0
Ingredient composition Ground corn Cottonseed hulls Soybean meal Rice hulls Ruminally protected fat Fish meal Fish oil Urea Limestone Dicalcium phosphate Trace mineral saltb Sodium sulfate Vitamin premixC Chemical analysis CP Total amino acids W, Ya of CP Essential fL4. oh of CP Nonessential AA, Oh of CP
ADF
.90
.45 .10
Control EP
.90
.45 .10
High EP 59.50 24.00 5.OO .05 5.OO 5.50 .10 .40 .45 -
aEP = ruminal escape protein. bTrace mineral salt provided the following per kilogram of diet: NaCl, 4.4 g; Mn, 14 mg; Fe, 8.5 mg; Cu, 2.3 mg; I. .23 mg; and Co, .24 mg. CVitaminpremix provided the following per kilogram of diet: vitamin A, 1,800IU; vitamin D,190 IU.
energy in feed fat, except for component glycerol, is utilized postruminally, increasing dietary fat should increase the requirement for high-quality escape CP. The following study was conducted to determine the effect of increased dietary fat and escape CP levels on apparent metabolic heat load and N utilization in thermally stressed lambs under conditions of controlled DMI.
Experimental Procedures Eight unshorn (approximately 2 cm of fleece depth) Suffolk wether lambs were equipped with plastic cannulas (1.3 cm i.d.1 in the dorsal sac of the rumen and approximately 12 cm from the pyloric sphincter in the abomasum (Komarek, 1981). After a 2-mo recovery period, lambs (57 initial BW = 28.8 kg) were allotted to either thermally neutral or high ambient temperature treatments (four lambs per treatment) such that body size was similar between the treatment groups. Within each ambient temperature treatment, lambs were randomly assigned to the four dietary treatments using a Latin square design. The study was conducted during the months of August, September, and October 1989; lambs on the high temperature treatments were kept in a n enclosed, ventilated room exposed to normal daily temperature
variation for the duration of the study. During cooler weather in October, a portable electric heater was used to maintain elevated room temperature. In the high-temperature room, daily maximum and minimum temperature averaged 30 f 3 and 24 f 2"C, respectively, and relative humidity averaged 79.1%. Lambs exposed to neutral temperature were kept in an air-conditioned room (21 k l"C1 throughout the study. All lambs were housed in individual wooden metabolism stalls with continuous illumination throughout the experiment. Dietary treatments consisted of either a control or high level of escape CP either with (high) or without (control) 5 %O of a sodium-alginate-encapsulated dry tallow (Booster Fat, Balanced Energy, Clinton, IA; Table 1). The control and high escape CP diets were formulated to meet approximately 90 and loo%, respectively, of the CP requirement and 100% of the requirements for energy, minerals, and vitamins for lambs (NRC, 19851, using maximum DMI assumptions that considered the effects of heat stress and restraint in stalls. Diets were also formulated to contain similar levels of ruminal fermentable energy and degradable CP. Fish meal was included in the high escape CP diets such that a ratio of approximately 70 g of escape CP per megacalorie of fat-derived ME would be maintained on the high escape CP-high fat diet.
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Control EPa
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BUNTING ET AL.
with HC1 for 22 h at 110°C (Spitz, 1973). Cystine, methionine, and tryptophan were not included in computations of total essential amino acids due to variable destruction of these amino acids during acid hydrolysis. Abomasal contents and bacterial pellets were analyzed for purines by the procedure of Zinn and Owens (1986) as modified by Ushida et al. (1985). Bacterial N and amino acids in abomasal contents were computed using the purine N:total N or amino acid ratios in isolated bacteria. Quantities of nutrients digested in the rumen were calculated by reference to Cr ratios in feed and abomasal contents. Statistical analyses were conducted using the GLM procedure of SAS (1985). A split-plot design was employed with temperature as the whole plot and escape CP and fat levels as the subplot. The effect of temperature was tested using animal within temperature level as the whole-plot error. Period was used as a blocking variable on the subplot, and the subplot analysis took into account the treatment restrictions of a Latin square design for a given temperature. The effects of period, fat, escape CP, fat x escape CP, and the interaction of each of these with temperature were tested using residual error as the subplot error term.
Results and Discussion Throughout the adjustment and collection periods, lambs kept at neutral temperature consumed their entire 12-hmeal within 1 to 2 h after feeding. Lambs kept at high temperature consumed approximately 80% of their meal within 2 h but, generally, required the entire 12-h feeding cycle to complete the meal. Ruminal insertion of refused feed was occasionally required for lambs kept at high temperature during extremely hot weather; however, feed administered in this manner represented less than 2 % of total DMI. Daily DMI averaged 606 g per lamb and represented a n average of 2.1% of BW. The marginal increases ( P e .05) in rectal temperature with elevated temperature suggest that the lambs were able to dissipate most of their excess heat load through panting, which is the principal mode of heat dissipation in thermally stressed ruminants (Table 2; NRC, 1981). Mean respiration rate was twofold greater ( P e .05) for lambs kept at high than for those kept at neutral temperatures. Lambs kept at high temperatures and those kept at neutral temperatures consumed similar ( P > .05) amounts of water. Elevated temperature increased (P e .05)evaporative water loss, computed as the difference between water intake and urine volume, but did not affect ( P >
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Each 16-d treatment period consisted of a 10-d dietary adjustment followed by 6 d of collection of excreta and digestive contents. During the final 5 d of the adjustment period and throughout the collection period, .45 g of chromic oxide was administered through the ruminal cannula at each feeding. Intake of all lambs was restricted to approximately 90% of that which was voluntarily consumed by lambs kept at high temperature. Feed was offered in equal portions at 12-h intervals. During the final 4 d of the adjustment period and throughout the collection period, feed not voluntarily consumed within a 12-h feeding cycle was manually inserted into the rumen through the ruminal cannula a t the subsequent feeding. Lambs were allowed unlimited access to water from plastic troughs. During the collection period, water refusals were weighed, and fresh water was provided a t each feeding. During the collection period, rectal temperature and respiration rate were recorded on d 1 at 2000, d 3 at 1600, and d 5 at 1200. Respiration rate was measured by the same person throughout the experiment and was recorded as the average time required for the lamb to complete 20 breaths. Immediately after these measurements, blood samples (10 mL) were collected into evacuated, heparinized tubes by jugular puncture. Daily fecal collections were dried for 7 d a t 50" C in a forced-air oven. Urine was collected into plastic vessels containing sufficient 6 N HC1 to maintain pH below 2.0 and an aliquot was retained each day and frozen. Daily feces and urine collections were pooled to yield individual lamb composites for chemical analyses. Also beginning on d 1, samples of ruminal fluid (50 mL) and abomasal contents (100 mL) were collected at 12-h intervals advanced 2 h daily for 6 d and frozen. Samples of abomasal contents were lyophilized and pooled on an equal-weight basis into individual lamb composites. Ruminal fluid samples were thawed and pooled on a n equal-volume basis into individual lamb composites. Ruminal fluid composites were centrifuged a t 1,000 x g for 15 min, and the resulting supernatant was centrifuged at 20,000 x g for 15 min, to obtain a bacteria-rich pellet. Pellets isolated from these ruminal fluid composites were used to determine purine N:total N ratios. Blood samples were centrifuged at 2,000 x g for 15 min, and plasma was retained for analysis. When appropriate, feed, excreta, bacterial pellets, and abomasal contents were analyzed for N (AOAC, 19841, ADF (Goering and Van Soest, 19701, and Cr (Kimura and Miller, 19571. Ruminal NH3 N and plasma urea N were determined as described previously (Sticker et al., 1991). Amino acids in abomasal contents were separated on a Beckman Model 6300 amino acid analyzer after hydrolysis
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ESCAPE PROTEIN AND FAT FOR LAMBS
Table 2. Physiological responses of lambs fed various levels of fat and ruminal escape protein (EP) at thermoneutral or high ambient temperatures
Item Respiration rat e, breathdmin Rectal temperature, "C Water intake, L/d Evaporative water loss, L/d
Ambient temperature
Fat level
EP level
Neutral High
Control High
Control High
50.7 39.5 3.3 1.o
105.3 39.8 3.7 1.7
75.8 39.6 4.0 1.2
80.2 39.7 3.0 1.5
70.1 39.6 3.4 1.3
79.9 39.6 3.6 1.5
.05)urine volume (data not shown). By comparison, Bhattacharya and Hussain (1974) reported threefold increases in respiration rates of Awasi wethers when subjected to similar environmental regimens. Although water intake was increased, rectal temperature was not influenced by elevated temperature in their study. At neutral temperature, diet did not influence respiration rates or rectal temperatures. Conversely, during high temperature, respiration rates and rectal temperatures were higher for lambs fed high than for those fed control escape CP when fed a high level of fat (128 vs 92.3 breathdmin and 39.9 vs 39.8"C, respectively) but lower when fed a low level of fat (93.4 vs 107.4 breathslmin and 39.7 and 39.9" C, respectively; temperature x fat x escape CP level interaction; P < .05).In addition, fat x escape CP level and temperature x escape CP level interactions ( P < .05)were observed for respiration rate. Moreover, water intake was lower (P < .05) for lambs fed high than for those fed control fat diets. The physiological significance of these dietary effects is not certain. Ruminal digestion of OM and ADF and total tract digestion of ADF were not affected (P > .05) by temperature or escape CP level [Table 3). The fiber digestibilities observed in this study are somewhat low but are consistent with those often reported when cottonseed hulls are fed in grainbased diets (Bunting et al., 1984; Kinser et al., 1988). Increased digestibility of DM and ADF is often reported for animals exposed to high temperature (NRC, 198 11. Enhanced nutrient digestibility has been attributed primarily to a reduction in the rate of feed passage through the digestive tract incident to heat-induced reductions in DMI and, potentially, decreased gut motility and rumination (NRC, 1981). Intake-induced effects on feed passage rate were eliminated in our study, because DMI was held constant. Moreover, most factors affecting digestion likely become less significant when diets of high potential digestibility, such as those used in our study, are fed (Beede and Collier, 1986).
Effectsa
4.4 T, .05 T, .42 F .22 T (P
.05)by temperature [Table 31, suggesting that the magnitudes of any potential changes in particulate passage incident to thermal stress were not sufficiently great to alter the escape of feed N from the rumen. Lambs fed the high escape CP diets had more (P < .05)total and dietary N reaching the abomasum and had a greater (P < .05) percentage of total N flow composed of dietary N than lambs fed control diets. High dietary fat also seemed to have decreased ruminal CP degradation, because lambs fed high-fat diets had a greater (P < .05)amount and percentage of total N and a greater (P < .05)amount and percentage of dietary N reaching the abomasum than did lambs fed the control fat diet (Table 3). As a consequence, dietary N flow was greater and composed a greater percentage of total N flow in lambs fed high escape CP than in controls when fed with a
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T ' = temperature effect (P c ,051,F = fat level effect (P < ,051,F x P = fat x EP interaction interaction (P < ,051,and T x F x P = temperature x fat x EP interaction (P < ,051.
SE
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BUNTING ET AL.
Table 3. Daily intake, digestion, abomasal N flow, N excretion and retention, and plasma and ruminal N metabolites in lambs fed various levels of fat and ruminal escape protein (EP) at thermoneutral or high ambient temperatures Ambient temperature Item OM intake, g/d N intake, g/d Apparent digestion, YO of intake OM in rumen” ADF in rumen ADF in total tract Total abomasal N flow, g/d oh of intake Bacterial N flow, g/d Dietary N flow, g/d Oh of intake Bacterial efficiency, g of CP/100 g of apparently fermented OM N excreted, g/d Fecal Urinary N absorbed, g/d N retained, g/d O/O of intake YO of absorbed Ruminal NH3 N. mM Plasma urea N, mM
EP level
Fat level
Neutral
High
Control
High
Control
High
579.0 10.5
579.0 10.4
578.9 10.4
579.2 10.5
578.0 9.8
580.1 11.1
58.6 13.9 34.5 9.1 86.8 3.6 5.5 52.0
56.5 13.9 31.3 9.7 92.8 3.6 6.1 57.9
64.8 22.2 34.0 8.9 85.6 4.O 4.9 47.3
50.2 5.5 31.8 9.9 94.1 3.2 6.6 62.6
58.9 18.5 34.0 8.7 89.3 3.9 4.8 49.5
56.1 9.3 31.9 10.0 90.4 3.3 6.7 60.4
4.1 10.9 2.6 .44 4.1 .44 .55 5.4
F F
6.9
7.3
6.8
7.3
7.6
6.6
1.2
F
3.0 4.2 7.4 3.2 30.7 43.5 4.7 5.5
3.2 4.0 7.2 3.2 30.7 44.2 5.1 4.8
3.0 4.7 7.4 2.7 25.6 36.2 4.0 5.8
3.2 3.5 7.2 3.8 35.8 51.4 5.8 4.5
3.1 3.6 6.7 3.0 31.2 45.6 5.1 4.7
3.2 4.6 7.9 3.4 30.2 42.1 4.7 5.6
.23 .21 .21 .25 2.3 3.0 .98 .56
-
aP = EP effect (P < .051,F = fat level effect (P < ,051,F interaction (P < ,051. bCorrected for contribution of bacterial OM.
x
P
=
fat
x
EP interaction ( P < ,051,and T
SE -
-
x
Effectsa -
-
F, P F F, F x P F, P, F x P F, P, F x P x
P
F, P,T x P P F, T x P F, T x P F, T x P F F, P
P = temperature
x
EP
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somewhat low compared with a range of microbial efficiency values reported across a number of studies with cattle and sheep (Stern and Hoover, 1979). Because this likely results from the restricted DMI used in our study, the applicability of these efficiency values to similar diets at maximum DMI seems somewhat dubious. Fecal N excretion was not affected (P > .lo) by treatment (Table 3). Hence, the digestible fiber that apparently escaped ruminal fermentation in lambs fed high-fat diets did not seem to result in significant synthesis of microbial N in the large intestine through its compensatory fermentation in that organ. Compared with controls, lambs fed high-fat diets excreted less (P c .05) urinary N, retained more (P e .05) N, and retained a greater (P e .05) percentage of N both consumed and absorbed (Table 31. Glenn et al. (1977) observed a response of similar magnitude in lambs kept a t neutral temperature fed 5 to 6 % added fat as tallow or vegetable oil, when linseed meal protein was precoated with fat sources. Given its high energy density and low heat increment of feeding (Baldwin et al., 19801, fat should represent a plausible method for reducing metabolic heat production during periods of thermal stress. Skaar et al. (1989) reported increased
high-fat diet (8.2 vs 5.1 g N/d and 77.3 vs 56.1°/o, respectively), but both variables were similar to controls when fed without added fat (5.3 vs 4.6 g N/d and 55.8 vs 54.30/0, respectively; fat x escape CP interaction; P < .05).This suggests that the presence of high dietary fat was the primary determinant of the proportion of dietary N escaping the rumen. Because the proportion of dietary N escaping ruminal degradation was similar for the high escape CP and control diets when fed without added fat, the greater amount of dietary N reaching the abomasum of lambs fed the high escape CP diet seemed to be attributable primarily to the higher N content of this diet. Decreased ruminal OM fermentation resulted in reduced (P c .05) synthesis of bacterial N in lambs fed the high vs control fat diet (Table 3). As a result of the apparent interaction between ruminal energy level and CP solubility, bacterial N flow and efficiency of CP synthesis were lower for lambs fed high than for those fed control escape CP when fed with a high-fat diet (2.4vs 4.0 g of N/d and 5.9 vs 8.8 g of CP/lOO g of fermented OM, respectively) but greater when fed without added fat (4.2vs 3.7 g of N/d and 7.2 vs 6.5 g of CP/lOO g of fermented OM, respectively; fat x escape CP interaction; P c .051. These bacterial efficiency values seemed to be
ESCAPE PROTEIN AND FAT FOR LAMBS
There is evidence that a greater proportion of ruminal escape CP is required for a given level of performance under conditions of thermal stress than during thermal neutrality (Higginbotham et al., 1989; Taylor et al., 19911. It has been suggested that the proportion of dietary CP that is ruminally degraded increases during heat stress, as a result of decreased particulate passage rate (Christopherson, 1985). This would likely increase the production and subsequent absorption of NH3 N from the rumen, with corresponding increases in the synthesis and excretion of urea N. High-CP diets containing moderately low proportions of escape CP have been reported to be more detrimental to the lactation performance of thermally stressed dairy cattle than similar diets containing greater proportions of escape CP (Higginbotham et al., 19891. Because a constant CP: energy ratio was maintained in our study, the effects of proportion of escape CP were confounded with the percentage of total CP in the diet. Furthermore, with no demonstrated effect of temperature on ruminal CP degradability, it must be concluded that thermal stress increased the lamb's requirement for CP ke., amino acids) beyond that which could be supplied by the control escape CP diet at the level of DMI established in this experiment. This may indicate that thermal stress decreases the available amino acid pool for growth through increased protein turnover or increases the protein requirement for specific maintenance functions related to thermal stress. Ruminal NH3 N concentrations were similar ( P > .05) for lambs fed high vs control levels of escape CP but were higher (P e .05) for lambs fed high than for those fed control levels of fat. In spite of higher ruminal NH3 N concentrations, plasma urea N concentrations were lower (P < .05) for lambs fed high than for those fed control fat. This likely reflected the higher rates of N accretion observed for these lambs. Plasma urea N concentrations were higher (P e .051for lambs fed high than control levels of escape CP (Table 3). Amino acid profiles of isolated ruminal bacteria were essentially identical across diets (Table 4) and were quite similar to previously reported amino acid profiles of ruminal bacteria (Bergen et al., 1968). Accordingly, the dietary contributions to abomasal amino acid flow were estimated by subtracting the bacterial contribution to the passage of each amino acid. Patterns of amino acids flowing to the abomasum paralleled that observed for N and seemed to reflect dietary differences in amino acid content, suggesting relative uniformity in ruminal degradation of dietary amino acids. High levels of either fat or escape CP increased ( P e .05) both the total flow and that of dietary origin
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milk yields in cows fed 5 OO/ supplemental ruminally inert fat under moderately warm conditions (late spring and summer; 23°C daily average) but no response to supplemental fat in the winter. In contrast, Moody et al. (1967) exposed lactating cows to cool (15 to 24°C) outdoor conditions or chamber-controlled thermal stress (constant 32"C) while feeding diets containing 0 to 10% of either hydrogenated vegetable fat or soybean oil. Fat and temperature had independent effects on e n ergy-corrected milk yield, which was only marginally influenced by added lipid. However, the ruminal effects of such a high level of fat and disturbances in protein:energy ratio were not controlled in their study. Knapp and Grummer (199 1) similarly observed independent diet and temperature effects when lactating cows were exposed to thermal neutrality (constant 21"CI or chamber-controlled thermal stress (32"C 14 h/d and 26°C 10 h/d) either with or without 5 % of a mixture of ruminally protected fat and tallow. Similarly, results of the present study suggest that supplemental fat is equally beneficial under n e u tral or thermal stress conditions. Temperature did not affect (P e .051 the amount or efficiency of N retention by lambs. During thermal stress, dietary CP has been shown to be used with diminishing efficiency as dietary CP concentrations approach the animal's theoretical requirement (Ames et al., 1980). This is thought to be attributable to increased diversion of metabolic energy from growth to thermal regulation (NRC, 19811, resulting in a lower effective CP requirement to maintain a n optimal protein:energy ratio. Although they absorbed more ( P c .051 N, lambs fed high escape CP excreted more (P e .051 urinary N and, consequently, retained an amount of N similar ( P > .051 to the amount retained by controls (Table 3). However, lambs fed high escape CP excreted marginally more urinary N than controls at high temperature (4.2 vs 3.7 g of N/d, respectively) but substantially more N than controls a t neutral temperature (4.9 vs 3.5 g of N/d, respectively; temperature x escape CP interaction; P .: .05). As a result, compared with controls, lambs fed high escape CP retained more N when exposed to high temperature (2.8 vs 3.6 g of N/d, respectively) but less N at neutral temperature (3.3 vs 3.1 g of N/d, respectively; temperature x escape CP interaction; P .: .05). Similarly, lambs fed high escape CP retained a marginally greater percentage of both N intake and N absorbed than controls at high temperature (32.5 vs 29.0% and 45.2 vs 43.2010, respectively; temperature x escape CP interaction; P .: .05) but smaller percentages a t neutral temperature (28.0 vs 33.4% and 39.0 vs 47.9%, respectively; temperature x escape CP interaction; P e .05).
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BUNTING ET AL.
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greater for lambs fed high than for those fed control escape CP, respectively. Methionine, lysine, and threonine have been reported to be the limiting amino acids in microbial protein (Nimrick et al., 1970; Richardson and Hatfield, 1978). Given the amino acid flow observed in the present study, it does not seem likely that protein quality would have been a significant limiter of lamb growth responses.
Implications The results of this study suggest that supplemental fat is equally beneficial for N retention under thermally neutral or thermal stress conditions. Hence, management decisions on whether to include supplemental fat in the diets of thermally stressed ruminants should be based strictly on the cost-effectiveness of maintaining animal perform-
Table 4. Amino acid (AA) flow to the abomasum of lambs fed various levels of fat and ruminal escape protein (EP) at thermoneutral or high ambient temperatures Ambient temperature Item
Neutral
Total AA flow, g/d Total nonessential Total essential Arginine Histidine Isoleucine Leucine Lysine Phenylalanine Threonine Valine Dietary AA flow, g/d Total nonessential Total essential Arginine Histidine Isoleucine Leucine Lysine Phenylalanine Threonine Valine Dietary AA flow, oh of intake Total nonessential Total essential Arginine Histidine Isoleucine Leucine Lysine Phenylalanine Threonine Valine
&P = EP effect (P < ,051,F interaction (P c ,051.
34.2 17.3 16.9 1 .9 .98 1.8 3.8 2.3 1.9 1.8 2.1 17.4 9.1 8.3 .91
.BO .79 2.1 1.2 .92 .80 1 .o 40.8 40.3 41.3 31.5 42.2 42.7 43.4 46.7 39.5 40.3 43.2 =
Fat level
High 36.8 18.6 18.2 2.0 1.1 2.0 4.1 2.3 2.1 1.9 2.2 19.8 10.3 9.5 1.0 .68
.91 2.4 1.4 1.1 .90 1.2 46.6 45.8 47.5 35.7 48.1 49.7 50.4 53.4 45.5 46.1 50.4
Control
High
33.2 16.8 16.4 1.8 .95 1.8 3.6 2.3 1.9 1.8 2.0 14.4 7.6 6.8 .74 .53 .62 1.8 .95 .74 .62 .83 34.7 34.6 34.9 26.6 37.8 35.1 37.8 39.4 32.7 32.8 37.0
fat level effect P < ,051,F
x
P
=
EP level
37.8 19.2 18.6 2.1 1.1 2.0 4.2 2.4 2.1 2.0 2.3 22.8 11.8 11.0 1.2 .75 1.1 2.7 1.6 1.2 1.1 1.3 52.6 51.5 53.8 40.7 52.5 57.3 56.0 60.7 52.3 53.7 56.7
fat
x
Control
High
32.9 16.7 16.2 1 .e .94 1.8 3.7 2.1 1 .9 1.7 2.0 14.7 7.7 7.0 .70 .53 .66
1.9 .92 .80 .62 .85 42.4 41.8 43.1 30.8 44.9 44.9 46.3 50.6 40.8 40.6 45.2
EP interaction
(P c
SE
Effectsa
38.1 19.3 18.8 2.1 1.1 2.0 4.1 2.6 2.1 2.0 2.3 22.5 11.7 10.9 1.2 .75 1 .o 2.6 1.6 1.2 1.1 1.3 44.9 44.3 45.6 36.5 45.4 47.5 47.5 49.5 44.1 45.9 48.4
1.6 .85 .75 .09 .04 .08 .18 .13 .09 .08 .09 2.5 1.2 1.3 .15 .06 .16 .26 .22 .l6 .15 .16 6.9 6.4 2.5 6.1 4.7 10.3 6.0 11.6
,051,and
T
F, P F, P F, P F. P, T x F. P,T x F, P F, P P, F x P, F, P F. P F. P F, P, F x F, P, F x F, P, F x F, P, F x F, P, F x F, P, F, P, F, P, F, P, F, P, F, P,
F F F
x
F F
x
F
F, F F, F F, F F, F F, F F, F F, F F
x
7.6
F, F
9.2 7.8
F, F F, F
x x
x
F
=
x x x x x x
x
x x x x
F F T
F
x
P P P P P P P P P P P
P P P P P P P P P P
temperature
x
fat
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for total amino acids and total essential and nonessential amino acids. Flow of dietary total and total essential and nonessential amino acids as a percentage of amino acid intake was greater ( P e .05)for lambs consuming high than for those consuming control levels of fat. In addition, both the amount and percentage of amino acid intake of total and total essential and nonessential amino acids of dietary origin flowing to the abomasum were greater in lambs fed high escape CP than in controls when fed with high fat but were similar to controls when fed without added fat (fat x escape CP interaction; P < .05).The total quantities of either total essential or total nonessential amino acids reaching the abomasum were 16% greater for lambs fed high than for those fed control escape CP. Although flow of other individual essential amino acids was near to or less than this magnitude, the total amount of lysine and threonine reaching the abomasum was 24 and 18%
ESCAPE PROTEIN AND FAT FOR LAMBS
Literature Cited Ames, D. R., D. R. Brink, and C. L. Willms. 1980. Adjusting protein in feedlot diets during thermal stress. J. h i m . Sci. 50:l.
AOAC. 1984.Official Methods of Analysis (14th Ed.]. Association of Official Analytical Chemists, Arlington, VA. Baldwin, R. L., N. E. Smith, J. Taylor, and M. Sharp. 1980. Manipulating metabolic parameters to improve growth rate and milk secretion. J. h i m . Sci. 51:1416. Beede, D. K., and R. J. Collier. 1986.Potential nutritional strategies for intensively managed cattle during thermal stress. J. Anim. Sci. 62:543. Bergen, W. G., D. B. Purser, and J. H. Cline. 1968. Effect of ration on the nutritive quality of rumen microbial protein. J. Anim. Sci. 27:1497. Bhattacharya, A. N., and F. Hussain. 1974. Intake and utilization of nutrients in sheep fed different levels of roughage under heat stress. J. Anim. Sci. 38:877. Bunting, L. D., C. R. Richardson, and R. W. Tock. 1984.Digestibility of ozone-treated sorghum stover by ruminants. J. Agric. Sci. (Camb.) 102:747. Christopherson, R. J. 1985. The thermal environment and the ruminant digestive system. In: M. K. Yousef (Ed.) Stress Physiology in Livestock. Vol. 1. Basic Principles. pp 183-180. CRC Press, Boca Raton, FL. Glenn, B. P., D. G. Ely, and J. A. Boling. 1977. Nitrogen metabolism in lambs fed lipid-coated protein. J. A n h . Sci. 46:871. Goering, H. K., and P. J. Van Soest. 1970.Forage fiber analyses (Apparatus, reagents, procedures, and some applications). Agric. Handbook 379. ABS, USDA, Washington, DC. Higginbotham, G. E., M. Torabi, and J. T. Huber. 1989.Influence of dietary protein concentration and degradability on performance of lactating cows during hot environmental temperatures. J. Dairy Sci. 72:2554. Kimura, F. T., and V. L. Miller. 1957.Improved determination of chromic oxide in cow feed and feces. J. Agric. Food Chem. 5:216.
Kinser, A. R., G.C. Fahey, Jr., L. L. Berger, and N. R.Merchen. 1988. Low-quality roughages in high-concentrate pelleted diets for sheep: Digestion and metabolism of nitrogen and energy as affected by dietary fiber concentration. J. Anim. sci. 66:487. Knapp, D. M., and R. R. Grummer. 1991. Response of lactating dairy cows to fat supplementation during heat stress. J. Dairy Sci. 74:2573. Komarek, R. J. 1981.Rumen and abomasal cannulation of sheep with specially designed cannulas and a cannula insertion instrument. J. Anim. Sci. 53790. Moody, E. G.,P. J. Van Soest, R. E. McDowell, and G. L. Ford. 1967.Effect of high temperature and dietary fat on performance of lactating cows. J. Dairy Sci. 50:1909. Nimrick, K. E, E. E. Hatfield, J. Kaminski, and F. N. Owens. 1970.Quantitative assessment of supplemental amino acid needs for growing lambs fed urea as the sole nitrogen source. J. Nutr. 100:1293. NRC. 1981. Effect of Environment on Nutrient Requirements of Domestic Animals. National Academy Press, Washington, DC. NRC. 1 Q85.Nutrient Requirements of Sheep. National Academy Press, Washington, DC. Palmquist, D. L. 1984. Use of fats in diets for lactating dairy cows. In: J. Wiseman (Ed.) Fats in Animal Nutrition. pp 357-381. Butterworths, London. Richardson, C. R.. and E. E. Hatfield. 1978.The limiting amino acids in growing cattle. J. Anim. Sci. 46:740. SAS. 1985. SAS User’s Guide: Basics. SAS Inst. Inc., Cary, NC. Skaar, T. C., R. R. Gnunmer, M. R. Dentine, and R. H. Stauffacher. 1989.Seasonal effects of prepartum and postpartum fat and niacin feeding on lactation performance and lipid metabolism. J. Dairy Sci. 72:2028. Spitz, H. D. 1973. A new approach for sample preparation of protein hydrolyzates for amino acid analysis. Anal. Biochem. 56:66. Stem, M. D., and W. H. Hoover. 1979. Methods for determining and factors affecting rumen microbial protein synthesis: A review. J. Anim. Sci. 49:1590. Sticker, L. S.,L. D. Bunting, W. E. Wyatt, and G. W. Wolfrom. 1991. Effect of supplemental lysocellin and tetronasin on growth, ruminal and blood metabolites, and ruminal proteolytic activity in steers grazing ryegrass. J. Anim. Sci. 6s: 4273.
Taylor, R. B.,J. T. Huber, R. A. Gomez-Alarcon, F. Wiersma, and X. Pang. 1991. Influence of protein degradability and evaporative cooling on performance of dairy cows during hot environmental temperatures. J. Dairy Sci. 74:243. Ushida, K., L. Bernadette, and J.-P. Jouany. 1985.Determination of assay parameters for RNA analysis in bacterial and duodenal samples by spectrophotometry. Influence of sample treatment and preservation. Reprod Nutr. Dev. 25:1037. Zinn, R. A., and F. N. Owens. 1986.A rapid procedure for purine measurement and its use for estimating net ruminal protein synthesis. Can. J. Anim. Sci. 66:157.
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ance through increased dietary energy density when heat-induced decreases in dry matter intake occur. These data further suggest that, at restricted dry matter intake, diets of thermally stressed, growing ruminants should be formulated to contain a higher level of crude protein (CPI by means of an increased amount and proportion of escape CP. However, diet fermentability, amino acid content and intestinal availability of escape CP, and level of animal performance will ultimately determine the optimum dietary CP concentration and proportion of escape CP.
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