U t i l i z a t i o n of Starea, Urea, or S o y b e a n Meal in C o m p l e t e Rations for Lactating D a i r y Cows G. M. JONES 1, C. STEPHENS, and BEVERLY KENSETT Crampton Nutrition Laboratory Department of Animal Science Macdonald Campus of McGill University Ste. Anne de Bellevue,Quebec Hgx 3MI, Canada ABSTRACT
ration for lactation should contain at least 14% CP, with 15% CP being recommended for cows producing more than 20 kg milk daily and 16% for cows yielding over 30 kg per day (19). During early lactation a 15.8% CP ration resulted in higher milk production than a ration containing 13.9% CP (10). Thus, the question of replacing part of the protein with NPN is in doubt. Utilization of urea rations for milk production has been improved by use of a mixture of gelatinized starch and urea, processed through an extruder cooker (13). Rumen ammonia concentrations were reduced when this mixture was incubated with rumen microorganisms (14). The objective of our study was to compare milk production and utilization of dietary nitrogen between 15.5% CP rations with supplemental nitrogen supplied totally by soybean meal, urea, or Starea, and between the high CP rations and a ration containing 12.4% CP. All protein is reported on a dry matter basis.
Three complete rations containing 15.8% of the dry matter as crude protein were compared to a 14.5% crude protein basal ration (dry matter basis) through eight Holstein cows in a replicated 4 × 4 Latin square design. The high protein rations contained supplemental nitrogen totally from soybean meal, urea, or Starea, the latter two providing 16 and 22% of total ration nitrogen, respectively. Concentrates were mixed with wilted alfalfa-bromegrass silage and complete rations fed ad lib±turn. Data were collected during the last week of each 28 days. Ration had no effect on milk yield, composition of fat or protein, or apparent digestibility of dry matter, crude protein, or acid detergent fiber. Weight gains and dry matter intake were greatest with the soybean meal ration. Intake of the low protein ration was depressed. There were no significant differences between the high protein rations for efficiency of nitrogen utilization.
EXPERIMENTAL PROCEDURES
INTRODUCTION
Animals
For years urea has been advocated as a supplemental nitrogen source for lactating dairy rations when natural protein supplements are costly. However, urea is utilized less efficiently than natural plant proteins such as soybean meal for milk production (12). It has been suggested that rumen ammonia concentrations accumulate when dry matter of the ration contains more than 13% crude protein (CP) and that ammonia from nonprotein nitrogen (NPN) in these rations is not utilized by rumen microorganisms (21). The dry matter of a dairy Received May 16, 1974. ~Present address: Department of Dairy Science, Virginia Polytechnic Institute and State University, Rlacksburg 24061.
Eight lactating Holstein cows averaging 30.4 ± 2.6 kg milk daily, 3.3 ± .5% milk fat, 3.5 ± .2% milk protein, and 77.2 ± 33.8 days in milk were assigned randomly to four experimental groups. Each group of two cows was fed each experimental ration during 28-day periods, the first 21 days serving as the adaptation period. Rations were assigned randomly to each group in a Latin square design. Rations
The four experimental rations were fed as complete rations by combining concentrates with wilted alfalfa-bromegrass silage. Total rations were formulated to satisfy requirements of National Research Council (19) for daily milk yields of 20 to 30 kg. Treatments corn-
689
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JONES ET AL.
prised: (1) 15.5% CP with soybean meal as the supplemental nitrogen source, (2) 15.5% CP with urea providing 20% of the total ration nitrogen, (3) 15.5% with 20% of the total ration nitrogen supplied by Starea 2, and (4) a low protein ration formulated at the same CP as rations 2 and 3 but without the CP equivalent from supplemental NPN included (12.4% CP). Crude protein is percentage of ration dry matter. Rations were computer-formulated least-cost rations 3 and purchased from the same feed mill (Table 1). Complete rations were hand-mixed and of. fered ad libitum at two feedings per day. During the adaptation period, the two cows in each group were housed together in a pen and fed from a bunk. During the collection period, cows were individually stanchioned in the dairy barn with no bedding.
Sampling Collections were made on 4 consecutive days of each 4th wk. During this time daily weights 2Starea (72.4% crude protein equivalent) obtained from Far-Mar-Co., Inc., Hutchinson, KS. SMiracle Feeds Division, Ogilvie Flour Mills, Montreal, Quebec. 4 Ingrain and Bell Ltd., Montreal, Quebec. 5Milko-Tester Automatic, Foss Electric, Hillerod, Denmark. e Harlecon blood urea nitrogen, Canadian Laboratory Supplies, Ltd., Montral, Quebec.
were obtained for milk production, feed offered and refused, and urine and fecal excretion. Cows were implanted with 75 cm 3 hemostatic catheters 4 (26 F) on the first morning of the collection period for urinary collection. Representative samples of feed, orts, feces, and urine were saved for chemical analysis. On the 4th day of the collection period, plasma samples were obtained from each cow at 30 to 45 min postprandial. Cows were weighed on 2 consecutive days at the beginning of the experiment and at the end of each 28 days.
Chemical Analyses Complete rations, orts, and silage were analyzed for dry matter (DM) content by toluene distillation uncorrected for volatiles lost into the aqueous distillate (26). These feed materials plus feces were dried at 40 C for 48 h in a forced-air oven and then ground to pass a 1 mm screen. Concentrate and fecal DM content were determined by oven-drying at 100 C for 5 h (1). All samples were analyzed for nitrogen by Kjeldahl (1) while acid detergent fiber (ADF) and acid detergent lignin (ADL) were determined on feed and feces samples (25) and feed samples alone were assayed for calcium (1), phosphorus (1), and ethanol soluble nitrogen (11). Urine and milk were analyzed for nitrogen or nitrogen and fat s , respectively. Plasma urea was determined by the Fearon condensation with diacetyl monoxime method 6.
TABLE 1. Ingredient composition of concentrate rations. Concentrate ingredients
Soybean meal
Corn (%) Barley (%) Molasses (%) Soybean meal (%) Starea (%) Urea (%) Ground limestone (%) Dicalcium phosphate (%) Salt (%) Trace mineralsa (%) Vitamin A (IU/kg) Vitamin D3 (IU/kg)
22.6 55.0 8.0 11.O ...
... 2.0 . ".9 .1
aContaining Co, I2, Cu, Fe, Mn, Mg, Zn, K, and CI. Journal of Dairy Science Vol. 58, No. 5
Starea
Urea
72.3 4.0 8.0
71.3 13.0 8.0 . .
"9.75
Low protein 79.5 7.1 8.0 .
.
.
. .-.
"1.85 3.6 .55 1.2 .1
"3.6 .55 1.3 .1 .4,540 454
"3.6 .1 1.2 .1
NITROGEN USE IN COMPLETE RATIONS Statistical Analysis
691
Milk Production and Digestibility
Data were analyzed as a replicated 4 x 4 Latin square design, partitioning the effects due to squares, periods within squares, cows within squares, and treatments (23). Treatments within squares were included in the error source of variation, as the effect was small. Means were compared by Duncan's multiple range test. During the fourth collection period, one cow on the low protein ration encountered pneumonia, and missing values were estimated.
R ESU LTS Feed Composition
The average analyses over the four periods for individual feeds and complete rations are in Table 2. Variation within concentrates was small. However, the wilted alfalfa-bromegrass silage varied from period to period as evidenced by the high standard deviations. Ethanol soluble nitrogen content was high (77% of total nitrogen) in the silage. Approximately 50% of the nitrogen in the urea and Starea concentrates was recovered in this fraction. This was not unexpected as this fraction included prolamin, reduced ammonia, etc. Differences between complete rations were determined by removing differences between periods as a source of variation. The three high protein rations contained more nitrogen than the control or low protein ration. This ration contained 14.5% CP, which was 2.1 percentage units higher than desired. The reason for this discrepancy is unknown. The low protein ration was comprised of 53.1% of the DM from the wilted silage while the higher protein rations contained 55.2% of the DM from silage. Based upon nitrogen content of silage and individual concentrates, the low protein, soybean meal, urea, and Starea complete rations should have contained 12.3, 16.0, 15.4, and 15.7% CP, respectively. A more plausible explanation would be the possibility that samples of this ration, which were collected for analyses, were not representative. Samples were collected at time of feeding rather than immediately after mixing. All estimates of nitrogen utilization were based upon actual analysis.
There were no significant differences in milk production between either sources of supplemental nitrogen or ration protein (Table 3). Compared to soybean meal, reductions in milk yield were 9.3, 1.9, and 4.7% for low protein, urea, and Starea rations. Milk fat percentage was not influenced by ration, but milk protein content was reduced (P < .05) by the low protein ration. The coefficient of variation was 25.5% for milk fat percentage. Cows fed soybean meal consumed more DM (P < .05), which may explain the greater body weight gains (P < .05), than those fed other rations. Intakes of DM were similar between soybean meal and Starea rations. Starea intake also surpassed that from the low protein ration (P < .05). Losses in body weight with the Starea ration cannot be explained by milk production or feed consumption. There were no differences between rations for apparent digestibility of DM, CP, ADF, or cellulose.
Nitrogen Utilization
Nitrogen in the low protein ration was metabolized to a greater extent (P < .05) than nitrogen in the Starea ration (Table 4). The trend was similar for apparent biological value, except that the low protein ration surpassed all three high protein rations. Variability among treatments for nitrogen retention was considerable. Although differences were nonsignificant, inclusion of NPN in the ration tended to depress nitrogen retention. There were no differences between rations for conversion of ration DM or digestible DM to milk or feed nitrogen to milk nitrogen. The highest (P < .05) plasma urea was with the soybean meal ration. Reducing dietary crude protein content resulted in lower plasma urea.
DISCUSSION
Although the results were not significantly different, average daily milk yields with the three higher protein rations were approximately Journal of Dairy Science Vol. 58, No. 5
.= %
T A B L E 2. C h e m i c a l c o m p o s i t i o n of f e e d s t u f f s and e x p e r i m e n t a l c o m p l e t e r a t i o n s . < 0
Concentrate
Z 0
Dry m a t t e r ( % )
NitrogenC (%) Soluble n i t r o g e n (% of N) Crude p r o t e i n c (%) Acid d e t e r g e n t FiberC(%) Ligninc(%) CelluloseC(%) C a l c i u m c (%) P h o s p h o r u s c (%) TDNd(%)
Wilted silage
Low protein
32.0 -+ 3.8 b 2 . 4 2 -+ .54 76.7 ,+ 25.1 15.1
8 9 . 7 -+ .7 89.9 -+ .6 1.50,+ .05 2.74-+ .12 17.7 ,+ 8.3 13.8 -+ 9 . 0 9.4 17.1
41.0 7.9 33.1 .95 .33 56.3
3.2 .5 2.7 1.59 .31 82.4
,+ 2.8 -+ .7 -+ 3.1 +- .24 ,+ .01 ,+ 13.7
,+ -+ -+ +-+ ,+
Soybean meal
.6 5.2 ,+ .2 .9 ,+ .4 4.3 ,+ .04 1.16 -+ .01 .54,+ .4 81.1 -+
Soybean meal
Urea
Starea
SE a
8 9 . 7 -+ 1.0 9 0 . 0 ,+ .8 2.53 ,+ .05 2.62 ,+ .05 4 6 . 8 ,+ 5.5 4 8 . 6 ,+ 7.0 15.8 16.4
43.3 2.32* 64.3 14.5
42.0 252* 52.4 15.8
41.0 2.54* 86.2 15.9
42.6 83.4 15.8
1,27 .04 11,02
4 . 0 ,+ .6 ,+ 3.4 +1.64,+ .42 ,+ 81.8 ,+
28.8 5.7 23.1 1.16 .32 62.4÷
30.1 5.8 24.3 1.07 .39 68.1,
29.4 5.6 23.8 1.16 .36 63.5 +
29.6 5.7 23.8 1.15 .35 63.T
Urea
.5 .1 .6 .05 .04 .5
Complete rations Low protein
Starea
.5 3.4 .2 .6 .4 2.8 .03 1.59 .01 .40 .3 8 2 . 4
,+ ± +,+ ,+ -+
.5 .1 .3 .10 .02 .2
a S t a n d a r d e r r o r o f t r e a t m e n t m e a n s for c o m p l e t e rations. b M e a n -+ SD. CDry m a t t e r basis. d T D N e s t i m a t e d for silage and c o m p l e t e r a t i o n s b y p e p s i n d i g e s t i o n (9) a n d for c o n c e n t r a t e s b y p r e d i c t i o n f r o m c e l l u l o s e c o n t e n t (5). ++Within c o m p l e t e rations, m e a n s n o t h a v i n g a c o m m o n s u p e r s c r i p t w e r e s i g n i f i c a n t l y d i f f e r e n t (P < .05).
2.52t
.88 .20 ,71 .03 .01 1,22
Z
>
NITROGEN USE IN COMPLETE RATIONS
693
TABLE 3. Milk yield and composition, weight changes, voluntary intake, and apparent digestion coefficients of cows fed experimental complete rations. Complete rations
Milk yield (kg/day) Milk Fat (%) Milk protein (%) Average gain (kg/day) Dry matter intake kg/100 kg body wt. kg/day Apparent digestion coefficients (%) Dry matter Crude protein Acid detergent fiber Acid detergent cellulose
Low protein
Soybean meal
Urea
Starea
SEa
23.4 3.30 2.69+ -.05~
25.8 3.31 2.88* .91,
25.3 2.99 2.79* 0+
24.6 3.08 2.82* -.36+
1.02 .14 .03 .30
2.51+ 15.0~
2.85¢ 17.2,
15.7+*
2.75** 16.5**
62.6 60.0
64.3
44.9 52.0
46.2 53.0
63.2 65.1 45.6 53.9
63.7 63.7 47.4 55.2
2.66+,
66.8
.05 .30 1.47 2.10 2.24 1.97
aStandard error of treatment means. +**Means not having a common superscript were significantly different (P < .05).
10% greater t h a n w h e n the ration c o n t a i n e d 14.5%. T h e data t e n d to s u p p o r t the findings of G a r d n e r and Park (10) w h e r e milk and solidsn o t - f a t p r o d u c t i o n were increased b y a 15.5% CP ration over a ration c o n t a i n i n g 13.2% CP. A 14.4% CP ration was i n t e r m e d i a t e . Cows received each ration in t h e c u r r e n t s t u d y for o n l y 4 w k w h i c h may have i n f l u e n c e d t h e response.
In contrast, Caffrey et al. (4) f o u n d t h a t r u m e n m i c r o o r g a n i s m s f r o m s h e e p had a d j u s t e d to urea-rich diets w i t h i n 13 to 19 days for in vitro and in vivo studies, respectively. Van H o r n et al. (24) o b s e r v e d t h a t m o s t o f the s p r e a d in milk p r o d u c t i o n b e t w e e n c o n t r o l and urea-fed c o w s o c c u r r e d w i t h i n the first 20 days a n d t h a t this spread was m a i n t a i n e d or n a r r o w e d a f t e r
TABLE 4. Utilization of dietary nitrogen from experimental complete rations. Complete rations
Metabolizable nitrogenb Apparent biological value c Nitrogen retentiond g/day % of NI Feed efficiency FCM/DM intake e FCM/digestible DM intake milk nitrogen/feed nitrogen Plasma urea (mg/100 ml)
Low protein
Soybean meal
Urea
Starea
SE a
35.3* 60.7+
30.8~* 46.3*
28.9++ 46.0*
27.2* 43.5*
2.16 2.67
19.5 5.0
20.2 3.4
8.0 1.5
9.5 1.3
3.78 2.60
1.30 2.17 28.5 13.0.
1.28 2.05 27.1 14.1.
.09 .16 1.08 .44
1.40 2.25 30.8 10.8"
1.44 2.26 27.7
15.9.
aStandard error of treatment means. bMetabolizable nitrogen = Nitrogen intake (NI) - [fecal nitrogen (FN) + urinary nitrogen (UN)]/NI X 100. CApparent biological value = Nitrogen retention + milk nitrogen (MN)/NI-FN × 100. dNitrogen retention represents nitrogen deposited in the body and is derived from NI - (FN + UN + MN). e4% fat-corrected milk (kg) per dry matter intake (kg). +*¢Means not having a common superscript were significantly different (P < .05). Journal of Dairy Science Vol. 58, No. 5
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JONES ET AL.
this time. In our study milk production was not recorded until after a 21 day adjustment to changes in complete rations. Knott et al. (17) observed that urea-containing concentrates were less effective in maintaining milk production but that the differences were nonsignificant when the total ration DM contained 13.0 or 14.9% CP. Subsequently Clark et al. (6) concluded that urea nitrogen was utilized less efficiently than nitrogen from soybean meal. Earlier studies showed that a urea ration produced slightly less milk and cows were less persistent compared to a ration comprised of natural plant proteins (2). Bartlett and Blaxter (3) observed a slight decrease in milk production to Urea, with the greatest reduction occurring in high-producing cows. Huber et al. (16) fed rations where urea supplied 0, 11, 22, 38, or 48% of the ration nitrogen and found a significant decrease in milk yield when urea supplied 22% of the nitrogen and marked depressions at 38 and 48%. For this reason our rations were formulated so that NPN sources would supply no more than 20 to 22% of the total ration nitrogen. We estimate that urea and Starea supplied 16 and 22% of the nitrogen. Utilization of urea nitrogen or its retention for utilization by animal tissues was slightly inferior to all plant proteins. This may have been due to urea's rapid hydrolysis as reviewed by Helmer and Bartley (12). Conrad and Hibbs (8) reported that approximately 32% of the dietary nitrogen was converted to nitrogen of milk and tissue when the ration was comprised of only plant proteins compared to 29 to 32% with high urea, high grain concentrates. In our study both dietary and absorbed nitrogen from the low protein ration were used more efficiently for nitrogen of milk and tissue. Soybean meal was slightly superior to NPN rations. In steers urea had to supply more than 20% of the total dietary nitrogen before efficiency of nitrogen metabolism was reduced (7). Expanded corn plus urea was developed to reduce ruminal ammonia, and this decrease has been observed in in vitro studies (14). The advantageous use of urea is restricted to conditions where rumen ammonia concentrations would be below optimal for rumen bacterial growth (18), perhaps as low as 7 mg rumen ammonia per 100 ml (20). Using published Journal of Dairy Science Vol. 58, No. 5
equations (22), we estimate that rumen ammonia in cows fed low protein, urea, Starea, and soybean meal rations were 9.3, 12.2, 11.9, and 11.8 mg/100 ml. The resistance of protein to attack by rumen microorganisms was correlated negatively with protein solubility (15). The NPN-contalning rations in this study were much higher in ethanol soluble nitrogen. It is unfortunate that our low protein complete ration was 14.5% CP since it complicates interpretation of results. There appeared to be a slight improvement in milk production with the NPN-containing rations, inferring that NPN sources were utilized although not as efficiently as soybean meal. This response was apparently due to higher ration intakes as milk production per kilogram intake of dry matter were less with both NPN sources. Average daily gains were high with the soybean meal ration. Helmer et al. (13) found that cows fed soybean meal or Starea produced more milk and gained more weight than cows fed a urea supplement. Intake of the latter was reduced. This study suggests that there was little difference between Starea and urea when they supplied 16 to 22% of the nitrogen in lactating dairy rations. The following research is necessary: (1) to investigate differences in concentrations of rumen ammonia and acid-detergent insoluble nitrogen between urea, Starea, and soybean meal when supplied in complete rations at (a) varying dietary crude protein content, (b) when the NPN sources are substituted at varying crude protein equivalent, and (c) for various grains and forages; (2) to establish if Starea can comprise a greater proportion of nitrogen of the total ration than urea; and (3) to make comparisons between Starea, urea, and soybean meal fed for at least one complete lactation.
ACKNOWLEDGMENT
Financial support was provided by Delmar Chemicals Ltd., LaSalle, Quebec. The authors are grateful for the technical assistance of B. Pettinger, Denise Gaulin, and B. Dolgowicz, supervision of the feeding and management of cows by G. Beaulieu and D. Hatcher, and computer formulation of concentrate rations by W. J. Esdale.
NITROGEN USE IN COMPLETE RATIONS REFERENCES
1. Association of Official Agricultural Chemists. 1970. Official methods of analysis, l l t h ed. Washington, DC. 2. Archibald, J. G. 1943. Feeding urea to dairy cows. Massachusetts Agr. Exp. Sta. Bull. 406. 3. Bartlett, S., and K. L. Blaxter. 1947. The value o f urea as a substitute for protein in the rations of dairy cattle. I. Field trials with dairy cows. J. Agr. Sci. 37:32. 4. Caffrey, P. J., E. E. Hatfield, H. W. Norton, and U. S. Garrigus. 1967. Nitrogen metabolism in the ovine. I. Adjustment to a urea-rich diet. J. Anim. Sci. 26:595. 5. Chandler, P. T., and H. W. Walker. 1972. Generation of nutrient specifications for dairy cattle for computerized least cost ration formulation. J. Dairy Sci. 55:1741. 6. Clark, J. H., S. L. Spahr, and R. G. Derrig. 1973. Urea utilization by lactating cows. J. Dairy Sci. 56:763. 7. Coleman, S., and K. M. Barth. 1974. Nutrient digestibility and N-metabolism by cattle fed rations based on urea and corn silage. J. Anim. Sci. 39:408. 8. Conrad, H. R., and J. W. Hibbs. 1968. Nitrogen utilization by the ruminant. Appreciation of its nutritive value. J. Dairy Sci. 51:276. 9. Donefer, E., E. W. Crampton, and L. E. Lloyd. 1966. The prediction of digestible energy intake potential (NVI) o f forages using a simple in vitro technique. Proc. Int. Grasslands Congr. 10:442. 10. Gardner, R. W., and R. L. Park. 1973. Protein requirements of cows fed high concentrate rations. J. Dairy Sci. 56:390. 11. Gonske, R. G., and D. R. Keeney. 1969. Effect of fertilizer nitrogen, variety, and maturity on the dry matter yield and nitrogen fractions o f corn grown for silage. Agron. J. 61:72. 12. Helmer, L. G., and E. E. Bartley. 1971. Progress in the utilization of urea as a protein replacer for ruminants. A review. J. Dairy Sci. 54:25. 13. Helmer, L. G., E. E. Bartley, and C. W. Deyoe. 1970. Feed processing. VI. Comparison of Starea, urea, and soybean meal and protein sources for lactating dairy cows. J. Dairy Sci. 53:883. 14. Helmer, L. G., E. E. Bartley, C. W. Deyoe, R. M.
15.
16.
17. 18. 19.
20.
21.
22. 23.
24.
25.
26.
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Meyer, and H. B. Pfost. 1970. Feed processing. V. Effect of an expansion-processed mixture of grain and urea (Starea) on nitrogen utilization in vitro. J. Dairy Sci. 53:330. Hendrickx, H. and J. Martin. 1963. In vitro study of the nitrogen metabolism in the rumen. Compt. Rend. Rech., Inst. Rech. Sci. 2nd Agr., Bruxelles 31:1. (As cited by Hungate, R. E. 1966. The rumen and its microbes. Academic Press, New Vork.) Huber, J. T., R. A. Sandy, C. E. Polan, C. T. Bryant, and R. E. Blaser. 1967. Varying levels of urea for dairy cows fed corn silage as the only forage. J. Dairy Sci. 50:1241. Knott, F. N., C. E. Polan, and J. T. Huber. 1972. Further observations on utilization of urea by lactating cows. J. Dairy Sci. 55:466. Lampila, M. 1972. Practical nonprotein-N-feeding to ruminants. World Rev. Anim. Prod. 8:28. National Academy of S c i e n c e s - National Research Council. 1971. Nutrients requirements of domestic animals. Nutrient requiremenys of dairy cattle. No. 3. Washington, DC. Oyaert, W., and J. H. Bouckaert. 1960. Quantitative aspects of food digestion in the rumen. Zentr. Veterinarmedizin 7:929. (As cited by Lampila 1972.) Roffler, R. E., and L. D. Satter. 1973. Influence of ration composition on ruminal ammonia concentration. J. Dairy Sci. 56:663. (Abstr.) Satter, L. D., and R. E. Roffler. 1973. Using NPN in the dairy cow ration. Page 45 in Proc. 34th Minn. Nutr. Conf. Bloomington, MN. Steel, R. G. D., and J. H. Torrie. 1960. Principles and procedures o f statistics. McGraw-Hill Book Co., New York, NV. Van Horn, H. H., C. F. Foreman, and J. E. Rodriguez. 1967. Effect of high-urea supplementation on feed intake and milk production o f dairy cows. J. Dairy Sci. 50:709. Van Soest, P. J. 1963. Use of detergents in the analysis of fibrous feeds. II. A rapid method for the determination of fiber and lignin. J. Ass. Offic. Agr. Chem. 46:829. Wilson, R. F., J. M. A. Tilley, and Maria A.-Th. Steemers. 1964. Comparison of oven drying and toluene distillation in the determination of the dry-matter content of silage. J. Sci. Food Agr. 15:197.
Journal of Dairy Science Vol. 58, No. 5
ration for lactation should contain at least 14% CP, with 15% CP being recommended for cows producing more than 20 kg milk daily and 16% for cows yielding over 30 kg per day (19). During early lactation a 15.8% CP ration resulted in higher milk production than a ration containing 13.9% CP (10). Thus, the question of replacing part of the protein with NPN is in doubt. Utilization of urea rations for milk production has been improved by use of a mixture of gelatinized starch and urea, processed through an extruder cooker (13). Rumen ammonia concentrations were reduced when this mixture was incubated with rumen microorganisms (14). The objective of our study was to compare milk production and utilization of dietary nitrogen between 15.5% CP rations with supplemental nitrogen supplied totally by soybean meal, urea, or Starea, and between the high CP rations and a ration containing 12.4% CP. All protein is reported on a dry matter basis.
Three complete rations containing 15.8% of the dry matter as crude protein were compared to a 14.5% crude protein basal ration (dry matter basis) through eight Holstein cows in a replicated 4 × 4 Latin square design. The high protein rations contained supplemental nitrogen totally from soybean meal, urea, or Starea, the latter two providing 16 and 22% of total ration nitrogen, respectively. Concentrates were mixed with wilted alfalfa-bromegrass silage and complete rations fed ad lib±turn. Data were collected during the last week of each 28 days. Ration had no effect on milk yield, composition of fat or protein, or apparent digestibility of dry matter, crude protein, or acid detergent fiber. Weight gains and dry matter intake were greatest with the soybean meal ration. Intake of the low protein ration was depressed. There were no significant differences between the high protein rations for efficiency of nitrogen utilization.
EXPERIMENTAL PROCEDURES
INTRODUCTION
Animals
For years urea has been advocated as a supplemental nitrogen source for lactating dairy rations when natural protein supplements are costly. However, urea is utilized less efficiently than natural plant proteins such as soybean meal for milk production (12). It has been suggested that rumen ammonia concentrations accumulate when dry matter of the ration contains more than 13% crude protein (CP) and that ammonia from nonprotein nitrogen (NPN) in these rations is not utilized by rumen microorganisms (21). The dry matter of a dairy Received May 16, 1974. ~Present address: Department of Dairy Science, Virginia Polytechnic Institute and State University, Rlacksburg 24061.
Eight lactating Holstein cows averaging 30.4 ± 2.6 kg milk daily, 3.3 ± .5% milk fat, 3.5 ± .2% milk protein, and 77.2 ± 33.8 days in milk were assigned randomly to four experimental groups. Each group of two cows was fed each experimental ration during 28-day periods, the first 21 days serving as the adaptation period. Rations were assigned randomly to each group in a Latin square design. Rations
The four experimental rations were fed as complete rations by combining concentrates with wilted alfalfa-bromegrass silage. Total rations were formulated to satisfy requirements of National Research Council (19) for daily milk yields of 20 to 30 kg. Treatments corn-
689
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JONES ET AL.
prised: (1) 15.5% CP with soybean meal as the supplemental nitrogen source, (2) 15.5% CP with urea providing 20% of the total ration nitrogen, (3) 15.5% with 20% of the total ration nitrogen supplied by Starea 2, and (4) a low protein ration formulated at the same CP as rations 2 and 3 but without the CP equivalent from supplemental NPN included (12.4% CP). Crude protein is percentage of ration dry matter. Rations were computer-formulated least-cost rations 3 and purchased from the same feed mill (Table 1). Complete rations were hand-mixed and of. fered ad libitum at two feedings per day. During the adaptation period, the two cows in each group were housed together in a pen and fed from a bunk. During the collection period, cows were individually stanchioned in the dairy barn with no bedding.
Sampling Collections were made on 4 consecutive days of each 4th wk. During this time daily weights 2Starea (72.4% crude protein equivalent) obtained from Far-Mar-Co., Inc., Hutchinson, KS. SMiracle Feeds Division, Ogilvie Flour Mills, Montreal, Quebec. 4 Ingrain and Bell Ltd., Montreal, Quebec. 5Milko-Tester Automatic, Foss Electric, Hillerod, Denmark. e Harlecon blood urea nitrogen, Canadian Laboratory Supplies, Ltd., Montral, Quebec.
were obtained for milk production, feed offered and refused, and urine and fecal excretion. Cows were implanted with 75 cm 3 hemostatic catheters 4 (26 F) on the first morning of the collection period for urinary collection. Representative samples of feed, orts, feces, and urine were saved for chemical analysis. On the 4th day of the collection period, plasma samples were obtained from each cow at 30 to 45 min postprandial. Cows were weighed on 2 consecutive days at the beginning of the experiment and at the end of each 28 days.
Chemical Analyses Complete rations, orts, and silage were analyzed for dry matter (DM) content by toluene distillation uncorrected for volatiles lost into the aqueous distillate (26). These feed materials plus feces were dried at 40 C for 48 h in a forced-air oven and then ground to pass a 1 mm screen. Concentrate and fecal DM content were determined by oven-drying at 100 C for 5 h (1). All samples were analyzed for nitrogen by Kjeldahl (1) while acid detergent fiber (ADF) and acid detergent lignin (ADL) were determined on feed and feces samples (25) and feed samples alone were assayed for calcium (1), phosphorus (1), and ethanol soluble nitrogen (11). Urine and milk were analyzed for nitrogen or nitrogen and fat s , respectively. Plasma urea was determined by the Fearon condensation with diacetyl monoxime method 6.
TABLE 1. Ingredient composition of concentrate rations. Concentrate ingredients
Soybean meal
Corn (%) Barley (%) Molasses (%) Soybean meal (%) Starea (%) Urea (%) Ground limestone (%) Dicalcium phosphate (%) Salt (%) Trace mineralsa (%) Vitamin A (IU/kg) Vitamin D3 (IU/kg)
22.6 55.0 8.0 11.O ...
... 2.0 . ".9 .1
aContaining Co, I2, Cu, Fe, Mn, Mg, Zn, K, and CI. Journal of Dairy Science Vol. 58, No. 5
Starea
Urea
72.3 4.0 8.0
71.3 13.0 8.0 . .
"9.75
Low protein 79.5 7.1 8.0 .
.
.
. .-.
"1.85 3.6 .55 1.2 .1
"3.6 .55 1.3 .1 .4,540 454
"3.6 .1 1.2 .1
NITROGEN USE IN COMPLETE RATIONS Statistical Analysis
691
Milk Production and Digestibility
Data were analyzed as a replicated 4 x 4 Latin square design, partitioning the effects due to squares, periods within squares, cows within squares, and treatments (23). Treatments within squares were included in the error source of variation, as the effect was small. Means were compared by Duncan's multiple range test. During the fourth collection period, one cow on the low protein ration encountered pneumonia, and missing values were estimated.
R ESU LTS Feed Composition
The average analyses over the four periods for individual feeds and complete rations are in Table 2. Variation within concentrates was small. However, the wilted alfalfa-bromegrass silage varied from period to period as evidenced by the high standard deviations. Ethanol soluble nitrogen content was high (77% of total nitrogen) in the silage. Approximately 50% of the nitrogen in the urea and Starea concentrates was recovered in this fraction. This was not unexpected as this fraction included prolamin, reduced ammonia, etc. Differences between complete rations were determined by removing differences between periods as a source of variation. The three high protein rations contained more nitrogen than the control or low protein ration. This ration contained 14.5% CP, which was 2.1 percentage units higher than desired. The reason for this discrepancy is unknown. The low protein ration was comprised of 53.1% of the DM from the wilted silage while the higher protein rations contained 55.2% of the DM from silage. Based upon nitrogen content of silage and individual concentrates, the low protein, soybean meal, urea, and Starea complete rations should have contained 12.3, 16.0, 15.4, and 15.7% CP, respectively. A more plausible explanation would be the possibility that samples of this ration, which were collected for analyses, were not representative. Samples were collected at time of feeding rather than immediately after mixing. All estimates of nitrogen utilization were based upon actual analysis.
There were no significant differences in milk production between either sources of supplemental nitrogen or ration protein (Table 3). Compared to soybean meal, reductions in milk yield were 9.3, 1.9, and 4.7% for low protein, urea, and Starea rations. Milk fat percentage was not influenced by ration, but milk protein content was reduced (P < .05) by the low protein ration. The coefficient of variation was 25.5% for milk fat percentage. Cows fed soybean meal consumed more DM (P < .05), which may explain the greater body weight gains (P < .05), than those fed other rations. Intakes of DM were similar between soybean meal and Starea rations. Starea intake also surpassed that from the low protein ration (P < .05). Losses in body weight with the Starea ration cannot be explained by milk production or feed consumption. There were no differences between rations for apparent digestibility of DM, CP, ADF, or cellulose.
Nitrogen Utilization
Nitrogen in the low protein ration was metabolized to a greater extent (P < .05) than nitrogen in the Starea ration (Table 4). The trend was similar for apparent biological value, except that the low protein ration surpassed all three high protein rations. Variability among treatments for nitrogen retention was considerable. Although differences were nonsignificant, inclusion of NPN in the ration tended to depress nitrogen retention. There were no differences between rations for conversion of ration DM or digestible DM to milk or feed nitrogen to milk nitrogen. The highest (P < .05) plasma urea was with the soybean meal ration. Reducing dietary crude protein content resulted in lower plasma urea.
DISCUSSION
Although the results were not significantly different, average daily milk yields with the three higher protein rations were approximately Journal of Dairy Science Vol. 58, No. 5
.= %
T A B L E 2. C h e m i c a l c o m p o s i t i o n of f e e d s t u f f s and e x p e r i m e n t a l c o m p l e t e r a t i o n s . < 0
Concentrate
Z 0
Dry m a t t e r ( % )
NitrogenC (%) Soluble n i t r o g e n (% of N) Crude p r o t e i n c (%) Acid d e t e r g e n t FiberC(%) Ligninc(%) CelluloseC(%) C a l c i u m c (%) P h o s p h o r u s c (%) TDNd(%)
Wilted silage
Low protein
32.0 -+ 3.8 b 2 . 4 2 -+ .54 76.7 ,+ 25.1 15.1
8 9 . 7 -+ .7 89.9 -+ .6 1.50,+ .05 2.74-+ .12 17.7 ,+ 8.3 13.8 -+ 9 . 0 9.4 17.1
41.0 7.9 33.1 .95 .33 56.3
3.2 .5 2.7 1.59 .31 82.4
,+ 2.8 -+ .7 -+ 3.1 +- .24 ,+ .01 ,+ 13.7
,+ -+ -+ +-+ ,+
Soybean meal
.6 5.2 ,+ .2 .9 ,+ .4 4.3 ,+ .04 1.16 -+ .01 .54,+ .4 81.1 -+
Soybean meal
Urea
Starea
SE a
8 9 . 7 -+ 1.0 9 0 . 0 ,+ .8 2.53 ,+ .05 2.62 ,+ .05 4 6 . 8 ,+ 5.5 4 8 . 6 ,+ 7.0 15.8 16.4
43.3 2.32* 64.3 14.5
42.0 252* 52.4 15.8
41.0 2.54* 86.2 15.9
42.6 83.4 15.8
1,27 .04 11,02
4 . 0 ,+ .6 ,+ 3.4 +1.64,+ .42 ,+ 81.8 ,+
28.8 5.7 23.1 1.16 .32 62.4÷
30.1 5.8 24.3 1.07 .39 68.1,
29.4 5.6 23.8 1.16 .36 63.5 +
29.6 5.7 23.8 1.15 .35 63.T
Urea
.5 .1 .6 .05 .04 .5
Complete rations Low protein
Starea
.5 3.4 .2 .6 .4 2.8 .03 1.59 .01 .40 .3 8 2 . 4
,+ ± +,+ ,+ -+
.5 .1 .3 .10 .02 .2
a S t a n d a r d e r r o r o f t r e a t m e n t m e a n s for c o m p l e t e rations. b M e a n -+ SD. CDry m a t t e r basis. d T D N e s t i m a t e d for silage and c o m p l e t e r a t i o n s b y p e p s i n d i g e s t i o n (9) a n d for c o n c e n t r a t e s b y p r e d i c t i o n f r o m c e l l u l o s e c o n t e n t (5). ++Within c o m p l e t e rations, m e a n s n o t h a v i n g a c o m m o n s u p e r s c r i p t w e r e s i g n i f i c a n t l y d i f f e r e n t (P < .05).
2.52t
.88 .20 ,71 .03 .01 1,22
Z
>
NITROGEN USE IN COMPLETE RATIONS
693
TABLE 3. Milk yield and composition, weight changes, voluntary intake, and apparent digestion coefficients of cows fed experimental complete rations. Complete rations
Milk yield (kg/day) Milk Fat (%) Milk protein (%) Average gain (kg/day) Dry matter intake kg/100 kg body wt. kg/day Apparent digestion coefficients (%) Dry matter Crude protein Acid detergent fiber Acid detergent cellulose
Low protein
Soybean meal
Urea
Starea
SEa
23.4 3.30 2.69+ -.05~
25.8 3.31 2.88* .91,
25.3 2.99 2.79* 0+
24.6 3.08 2.82* -.36+
1.02 .14 .03 .30
2.51+ 15.0~
2.85¢ 17.2,
15.7+*
2.75** 16.5**
62.6 60.0
64.3
44.9 52.0
46.2 53.0
63.2 65.1 45.6 53.9
63.7 63.7 47.4 55.2
2.66+,
66.8
.05 .30 1.47 2.10 2.24 1.97
aStandard error of treatment means. +**Means not having a common superscript were significantly different (P < .05).
10% greater t h a n w h e n the ration c o n t a i n e d 14.5%. T h e data t e n d to s u p p o r t the findings of G a r d n e r and Park (10) w h e r e milk and solidsn o t - f a t p r o d u c t i o n were increased b y a 15.5% CP ration over a ration c o n t a i n i n g 13.2% CP. A 14.4% CP ration was i n t e r m e d i a t e . Cows received each ration in t h e c u r r e n t s t u d y for o n l y 4 w k w h i c h may have i n f l u e n c e d t h e response.
In contrast, Caffrey et al. (4) f o u n d t h a t r u m e n m i c r o o r g a n i s m s f r o m s h e e p had a d j u s t e d to urea-rich diets w i t h i n 13 to 19 days for in vitro and in vivo studies, respectively. Van H o r n et al. (24) o b s e r v e d t h a t m o s t o f the s p r e a d in milk p r o d u c t i o n b e t w e e n c o n t r o l and urea-fed c o w s o c c u r r e d w i t h i n the first 20 days a n d t h a t this spread was m a i n t a i n e d or n a r r o w e d a f t e r
TABLE 4. Utilization of dietary nitrogen from experimental complete rations. Complete rations
Metabolizable nitrogenb Apparent biological value c Nitrogen retentiond g/day % of NI Feed efficiency FCM/DM intake e FCM/digestible DM intake milk nitrogen/feed nitrogen Plasma urea (mg/100 ml)
Low protein
Soybean meal
Urea
Starea
SE a
35.3* 60.7+
30.8~* 46.3*
28.9++ 46.0*
27.2* 43.5*
2.16 2.67
19.5 5.0
20.2 3.4
8.0 1.5
9.5 1.3
3.78 2.60
1.30 2.17 28.5 13.0.
1.28 2.05 27.1 14.1.
.09 .16 1.08 .44
1.40 2.25 30.8 10.8"
1.44 2.26 27.7
15.9.
aStandard error of treatment means. bMetabolizable nitrogen = Nitrogen intake (NI) - [fecal nitrogen (FN) + urinary nitrogen (UN)]/NI X 100. CApparent biological value = Nitrogen retention + milk nitrogen (MN)/NI-FN × 100. dNitrogen retention represents nitrogen deposited in the body and is derived from NI - (FN + UN + MN). e4% fat-corrected milk (kg) per dry matter intake (kg). +*¢Means not having a common superscript were significantly different (P < .05). Journal of Dairy Science Vol. 58, No. 5
694
JONES ET AL.
this time. In our study milk production was not recorded until after a 21 day adjustment to changes in complete rations. Knott et al. (17) observed that urea-containing concentrates were less effective in maintaining milk production but that the differences were nonsignificant when the total ration DM contained 13.0 or 14.9% CP. Subsequently Clark et al. (6) concluded that urea nitrogen was utilized less efficiently than nitrogen from soybean meal. Earlier studies showed that a urea ration produced slightly less milk and cows were less persistent compared to a ration comprised of natural plant proteins (2). Bartlett and Blaxter (3) observed a slight decrease in milk production to Urea, with the greatest reduction occurring in high-producing cows. Huber et al. (16) fed rations where urea supplied 0, 11, 22, 38, or 48% of the ration nitrogen and found a significant decrease in milk yield when urea supplied 22% of the nitrogen and marked depressions at 38 and 48%. For this reason our rations were formulated so that NPN sources would supply no more than 20 to 22% of the total ration nitrogen. We estimate that urea and Starea supplied 16 and 22% of the nitrogen. Utilization of urea nitrogen or its retention for utilization by animal tissues was slightly inferior to all plant proteins. This may have been due to urea's rapid hydrolysis as reviewed by Helmer and Bartley (12). Conrad and Hibbs (8) reported that approximately 32% of the dietary nitrogen was converted to nitrogen of milk and tissue when the ration was comprised of only plant proteins compared to 29 to 32% with high urea, high grain concentrates. In our study both dietary and absorbed nitrogen from the low protein ration were used more efficiently for nitrogen of milk and tissue. Soybean meal was slightly superior to NPN rations. In steers urea had to supply more than 20% of the total dietary nitrogen before efficiency of nitrogen metabolism was reduced (7). Expanded corn plus urea was developed to reduce ruminal ammonia, and this decrease has been observed in in vitro studies (14). The advantageous use of urea is restricted to conditions where rumen ammonia concentrations would be below optimal for rumen bacterial growth (18), perhaps as low as 7 mg rumen ammonia per 100 ml (20). Using published Journal of Dairy Science Vol. 58, No. 5
equations (22), we estimate that rumen ammonia in cows fed low protein, urea, Starea, and soybean meal rations were 9.3, 12.2, 11.9, and 11.8 mg/100 ml. The resistance of protein to attack by rumen microorganisms was correlated negatively with protein solubility (15). The NPN-contalning rations in this study were much higher in ethanol soluble nitrogen. It is unfortunate that our low protein complete ration was 14.5% CP since it complicates interpretation of results. There appeared to be a slight improvement in milk production with the NPN-containing rations, inferring that NPN sources were utilized although not as efficiently as soybean meal. This response was apparently due to higher ration intakes as milk production per kilogram intake of dry matter were less with both NPN sources. Average daily gains were high with the soybean meal ration. Helmer et al. (13) found that cows fed soybean meal or Starea produced more milk and gained more weight than cows fed a urea supplement. Intake of the latter was reduced. This study suggests that there was little difference between Starea and urea when they supplied 16 to 22% of the nitrogen in lactating dairy rations. The following research is necessary: (1) to investigate differences in concentrations of rumen ammonia and acid-detergent insoluble nitrogen between urea, Starea, and soybean meal when supplied in complete rations at (a) varying dietary crude protein content, (b) when the NPN sources are substituted at varying crude protein equivalent, and (c) for various grains and forages; (2) to establish if Starea can comprise a greater proportion of nitrogen of the total ration than urea; and (3) to make comparisons between Starea, urea, and soybean meal fed for at least one complete lactation.
ACKNOWLEDGMENT
Financial support was provided by Delmar Chemicals Ltd., LaSalle, Quebec. The authors are grateful for the technical assistance of B. Pettinger, Denise Gaulin, and B. Dolgowicz, supervision of the feeding and management of cows by G. Beaulieu and D. Hatcher, and computer formulation of concentrate rations by W. J. Esdale.
NITROGEN USE IN COMPLETE RATIONS REFERENCES
1. Association of Official Agricultural Chemists. 1970. Official methods of analysis, l l t h ed. Washington, DC. 2. Archibald, J. G. 1943. Feeding urea to dairy cows. Massachusetts Agr. Exp. Sta. Bull. 406. 3. Bartlett, S., and K. L. Blaxter. 1947. The value o f urea as a substitute for protein in the rations of dairy cattle. I. Field trials with dairy cows. J. Agr. Sci. 37:32. 4. Caffrey, P. J., E. E. Hatfield, H. W. Norton, and U. S. Garrigus. 1967. Nitrogen metabolism in the ovine. I. Adjustment to a urea-rich diet. J. Anim. Sci. 26:595. 5. Chandler, P. T., and H. W. Walker. 1972. Generation of nutrient specifications for dairy cattle for computerized least cost ration formulation. J. Dairy Sci. 55:1741. 6. Clark, J. H., S. L. Spahr, and R. G. Derrig. 1973. Urea utilization by lactating cows. J. Dairy Sci. 56:763. 7. Coleman, S., and K. M. Barth. 1974. Nutrient digestibility and N-metabolism by cattle fed rations based on urea and corn silage. J. Anim. Sci. 39:408. 8. Conrad, H. R., and J. W. Hibbs. 1968. Nitrogen utilization by the ruminant. Appreciation of its nutritive value. J. Dairy Sci. 51:276. 9. Donefer, E., E. W. Crampton, and L. E. Lloyd. 1966. The prediction of digestible energy intake potential (NVI) o f forages using a simple in vitro technique. Proc. Int. Grasslands Congr. 10:442. 10. Gardner, R. W., and R. L. Park. 1973. Protein requirements of cows fed high concentrate rations. J. Dairy Sci. 56:390. 11. Gonske, R. G., and D. R. Keeney. 1969. Effect of fertilizer nitrogen, variety, and maturity on the dry matter yield and nitrogen fractions o f corn grown for silage. Agron. J. 61:72. 12. Helmer, L. G., and E. E. Bartley. 1971. Progress in the utilization of urea as a protein replacer for ruminants. A review. J. Dairy Sci. 54:25. 13. Helmer, L. G., E. E. Bartley, and C. W. Deyoe. 1970. Feed processing. VI. Comparison of Starea, urea, and soybean meal and protein sources for lactating dairy cows. J. Dairy Sci. 53:883. 14. Helmer, L. G., E. E. Bartley, C. W. Deyoe, R. M.
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Meyer, and H. B. Pfost. 1970. Feed processing. V. Effect of an expansion-processed mixture of grain and urea (Starea) on nitrogen utilization in vitro. J. Dairy Sci. 53:330. Hendrickx, H. and J. Martin. 1963. In vitro study of the nitrogen metabolism in the rumen. Compt. Rend. Rech., Inst. Rech. Sci. 2nd Agr., Bruxelles 31:1. (As cited by Hungate, R. E. 1966. The rumen and its microbes. Academic Press, New Vork.) Huber, J. T., R. A. Sandy, C. E. Polan, C. T. Bryant, and R. E. Blaser. 1967. Varying levels of urea for dairy cows fed corn silage as the only forage. J. Dairy Sci. 50:1241. Knott, F. N., C. E. Polan, and J. T. Huber. 1972. Further observations on utilization of urea by lactating cows. J. Dairy Sci. 55:466. Lampila, M. 1972. Practical nonprotein-N-feeding to ruminants. World Rev. Anim. Prod. 8:28. National Academy of S c i e n c e s - National Research Council. 1971. Nutrients requirements of domestic animals. Nutrient requiremenys of dairy cattle. No. 3. Washington, DC. Oyaert, W., and J. H. Bouckaert. 1960. Quantitative aspects of food digestion in the rumen. Zentr. Veterinarmedizin 7:929. (As cited by Lampila 1972.) Roffler, R. E., and L. D. Satter. 1973. Influence of ration composition on ruminal ammonia concentration. J. Dairy Sci. 56:663. (Abstr.) Satter, L. D., and R. E. Roffler. 1973. Using NPN in the dairy cow ration. Page 45 in Proc. 34th Minn. Nutr. Conf. Bloomington, MN. Steel, R. G. D., and J. H. Torrie. 1960. Principles and procedures o f statistics. McGraw-Hill Book Co., New York, NV. Van Horn, H. H., C. F. Foreman, and J. E. Rodriguez. 1967. Effect of high-urea supplementation on feed intake and milk production o f dairy cows. J. Dairy Sci. 50:709. Van Soest, P. J. 1963. Use of detergents in the analysis of fibrous feeds. II. A rapid method for the determination of fiber and lignin. J. Ass. Offic. Agr. Chem. 46:829. Wilson, R. F., J. M. A. Tilley, and Maria A.-Th. Steemers. 1964. Comparison of oven drying and toluene distillation in the determination of the dry-matter content of silage. J. Sci. Food Agr. 15:197.
Journal of Dairy Science Vol. 58, No. 5
