Lactational Responses of Dairy Cows Fed Unsaturated Dietary Fat and Receiving Bovine Somatotropin' 0. A. STEGEMAN, D. P. CASPER.* D. J. SCHINGOETHE. and R. J. BAER3 ~aiv& e m oepartment South Dakota State University Bmkings 570074647 ABSTRACT
Feeding unsaturated dietary fat to lactating dairy cows receiving bST may effectively alter the fatty acid composition of milk fat. This was tested using 16 Holstein cows assigned to one of four treatments during midlactation. Treatments were control, control diet with 15.5 mg of bST/d per cow, dietary fat from sunflower seeds and bST, or dietary fat from safflower seeds and bST. Diets were formulated to contain 19%CP and contained 25% corn silage, 25% alfalfa hay, and 50% concentrate mix on a DM basis. Milk yield was not significantly higher when bST was administered and increased with added fat diets (29.5, 32.7,40.0, and 34.1 kg/d for the control, control with bST, d o w e r seed with bST, and safflower seed with bST treatments, respectively). Percentage of milk fat was similar for all treatments. Concentrations of long-chain and unsaturated fatty acids in milk were increased slightly by bST and substantially with added fat. Milk protein percentages were not influenced by bST but were reduced by approximately .2 unit with added fat. Added unsaturated dietary fat coupled with bST increased milk yield and produced a greater concentration of unsaturated fatty acids in milk. (Key words: unsaturated fatty acids, milk, bovine somatotropin)
Abbreviation key: C = control, C+ = control with bST, Saff+ = dietary fat from safflower seeds with bST, Sun+ = dietary fat from sunflower seeds with bST. INTRODUCTION
Consumers today are more health conscious and are demanding dairy products lower in milk fat, especially saturated fat. Presently, reductions 'in milk fat concentrations through nutritional modification are not feasible for the long-term health of the dairy cow. However, increasing the unsaturated fatty acid composition of milk fat is possible (3, 5). Manufacturing this milk into dairy products may offer a potential market for the dairy industry (3). Dietary manipulation is one of several methods to alter the fatty acid composition of milk Recent studies demonstrated that milk fat from dairy cows fed diets containing soybeans (12) or sunflower seeds (5, 17) contained greater concentrations of unsaturated fatty acids than that of cows fed diets without supplemental fat. Dairy producers may be able to customize the fatty acid profile of milk fat for dairy products by varying the fatty acid distribution of dietary fat fed to cows (3, 5). Many bST studies have shown increased milk yield (2, 16), but few studies have detailed data on the distributions of fat and protein fractions in milk from cows during long-term studies. In a short-term study, Eppard et al. (9) reported that, as dose of bST increased, the concentration of unsaturated fatty acids in milk fat increased. Baer et aL (4) Received October 25, 1991. reported that cows receiving 30.9 mg of bST/d Accepted March 2,1992. 'PUW with ~IXapproval of the director of the per cow in a long-term study had milk fat and South D h t a Agricultuxal Experiment Station as Publica- protein percentages similar to those of cows tion Number 2584 of the Journal Series. not receiving bST, but fatty acid and protein 'Present address: Ruminant Nutrition Laboratory, fractions were altered. Milk fat contained USDA-ARS, Building 162, Beltsville Agricaltural Regreater concentrations of long-chain and unsatsearch Center-East, Beltsville, MD 20705-2350. urated fatty acids, whereas casein as a percenth p r i n t requests. 1992 J Dairy Sci 75:1936-1945
1936
UNSATURATED DIETARY FAT AND SOMATOTROPIN
1937
age of total and true protein was lower for TABLE 1. Ingredient content of concentrate mixtures.' cows receiving bST. These changes in fat and protein were more pronounced in the first 6 wk C of WT administration when cows appeared to Insrrdient andC+ Sun+ Saff+ be in negative energy and protein balance. (% as mixed) Changes in the fatty acid composition of 492 34.0 32.9 Com, g r o u n d and shelled milk fat because of changes in ration composi34.5 35.6 Soybean meal, 44% 8 39.3 tion and administration of bST may be additive sllnflower seeds, rolled . . . 20.0 ... (3). New technologies may allow formulation safflower d, ... . . . 20.0 rolled 5 .o 5.0 5.0 of diets to alter the fatty acid composition of Liquid molasses 2.5 2.5 2.5 milk fat to meet the recommendations of many Limestone 1.0 1.o 1.0 Dicalcium phosphate human health professionals for reduced intake 1.o 1.0 1.0 Tracamingalized salt3 of saturated fats. The objective of this study Sodium bicarbonate 15 1.5 1.5 was to utilize available feed sources and tech- Magnesium oxide 5 .5 5 nologies to alter the fatty acid composition of 'Also added were 8818 IU of vitamin A, 1764 IU of milk fat. vitamin D, and 45 IU of vitamin E/Lg of mixtures.
-
MATERIALS AND METHODS
Sixteen Holstein cows (4 primiparous) in midlactation (75 to 173 DIM, average 104) were blocked by milk yield and parity and assigned randomly to one of four treatments. Treatments were control (C) diet containing corn and soybean meal as the main ingredients in the concentrate mix, C diet with 15.5 mg of bST/d per cow (C+),dietary fat from sunflower seeds with bST (Sun+), and dietary fat from safflower seeds with bST (Saff+). Injections of WT (American Cyanamid, Princeton, NJ) were administered subcutaneously at lo00 h daily in the pocket lateral to the tailhead, alternating sides daily, using 20-mm, 20-gauge needles. The 4 C treatment cows received 1 ml of sterile buffered saline daily. Total mixed diets were formulated (DM basis) to be isonitrogenous (19% CP) and consisted of 25% corn silage, 25% chopped alfalfa hay, and 50% of the respective concentrate mixtures. Rolled sunflower and safflower seeds were included at 20% of the concentrate mixture to replace portions of corn and soybean meal (Table 1). Sunflower and safflower seeds were chosen and because of their high fat content (M%) variation in fatty acid composition [>65 and >8O% linoleic acid (c18:2), respectively; Table 21. Limestone and MgO were included in the concentrate mixture to supply additional Ca and Mg to minimize alterations in rumen fermentation because of high fat diets (15). The experiment was divided into three periods. Period l (pretreatment) was l wk (wk 11 postpartum), during which all cows were fed
-
k = Control, C+ = control with bST, Sun+ = dietary fat from sunflower seeds with bST, and Saff+ = dietary fat from safflower seeds with bST. 3Cmtained (46): NaCl (97 to 98.5), I (.007), M n (M), Fe (m), Mg (.050), CU (.032), Co (.Oil), Zn
(.ow.
the herd ration; milk yield and composition data were collected to be used as covariates. Period 2 was the next 4 wk, when cows were allowed to adapt to the respective treatment diets. Period 3 was the 16wk experimental period, commencing with the daily injections of bST and collection of data. Cows were housed in a free-stall barn, and diets were fed once daily for ad libitum intake using Calan feeding doors (American Calan, Inc., Northwood, NH); amounts of feed fed and refused were recorded daily. Body weights were recorded during 3 consecutive d at the start of the experiment, then weekly, and on 3 consecutive d at the end of the experimental
period. Corn silage, alfalfa hay, and concentrate mixtures were sampled weekly throughout the experiment and frozen. Samples were combmed into monthly composites, dried at 5YC, and ground through an ultracentrifuge mill with a 1-mm screen (Brinkman Instruments Co., Westbury, NY). Dry matter, CP, ether extract, ash in feed samples and oilseeds, and Ca, P, and Mg in feed samples were analyzed according to the procedures of AOAC (1). Neutral detergent fiber, ADF, and permanganate lignin were determined by the proceJournal of Dairy Science Vol. 75, No. 7, 1992
1938
STEGEMAN ET AL.
TABLE2. Composition of sunflowerand safflowerseeds. Measurement
DM, % cp MIF
ADF Ether extract Ash
smower
Sunflower 94.3
-(%
Of
94.4
DM)
20.6 24.1 17.4 42.6 3.5
-
185 34.6 24.7 41 5 25
Fatty acid composition 140' .a2 16:O 2.66 16:l .I6 ... 17:O 18:O 1.92 8.68 18:1 18:2 29.13 .24 18:3 20 1 .88 22:o .38 .03 22: 1 24:O .23 Total fatty acids 44.33
.052 6.00 .36
.OS
2.83 .06
.29 4.33 19.58 65.71 .54 1.99 .86
.07 .51
.80
3.78 33.97 .10 .18
.I22 6.69 .14 .69 1.89 8.94 80.33
.09
.01 .13 42.29
24 .43 .21
.m
.31
~~
'Expressed as number of carb0nS:number of double bonds. 2 ~ are expressed ~ ~ as grams m per 100 g of total fatty acids.
milk fat content in the present study is based on the Mojonnier ether extraction -procedure (22). Milk samples were analyzed for fatty acid composition by GLC separation of butyl esters (5). Nitrogen distributions were determined by the Rowland method (19), and the individual milk protein fractions were separated by electrophoresis using a gradient SDSPAGE system (13). Samples of ruminal fluid were taken four times during the experiment, approximately once every 4 wk. Two to 4 h after feeding, samples were collected via an esophageal tube into bottles containing .5 ml of saturated HgCl2. Samples were analyzed for pH, fitered through four layers of cheesecloth, and prepared for VFA and ruminal ammonia determinations (5). Samples of jugular vein blood were drawn into serum separation tubes at the time of rumen sampling. They were centrifuged for 20 min at 850 x g, and the Supernatant fractions were decanted and frozen at -2o'C. Jugular serum samples were analyzed for urea N concentration (5). Statlsticai Analysis
dures of Robertson and Van Soest (18). Fatty acid content in feed samples and oilseeds was determined as described by Sukhija and Palmquist (23). Cows were milked twice daily; milk weights were recorded at each milking throughout the experimental period. Two 24-h (a.m. and p.m.) milk samples were collected from each cow during the prematment week. One 24-h (a.m. plus p.m.) milk sample was collected each week throughout the experimental period. Samples were analyzed for milk fat, protein, SNF, and lactose by midinfiared spectrophotometry (Multispec, Foss Food Technology Corp., Eden Prairie, MN) according to AOAC procedures (1). This method uses two filters (A and B) with corresponding wavelengths of 5.73 pm and 3.4 to 3.5 pm. A companion study (22) was conducted to evaluate different methods of milk fat determination. Results indicated that the midinfrared spectroscopic method underestimated milk fat content when the concentration of unsaturated fatty acids was high. Therefore, Journal of Dairy Science Vol. 75, No. 7, 1992
Milk yield and composition data were adjusted by analysis of covariance (21) using milk yield and composition data collected during the pretreatment period as covariates. All data were subjected to least squares ANOVA for a split-plot design; the main plot was arranged in a randomized complete block design with week of experiment as the subplot (21) and analyzed by the general linear models procedure (20). Results are expressed as least squares means. Sources of variation were covariate, replication, treatment, experimental week, and the interaction of treatment by experimental week. Contrasts of 1) C versus C+, 2) C+ versus Sun+ and Sa+, and 3) Sun+ versus Saff+ were used to separate treatment effects in the main plot (21). Significance was declared at P < .05 unless otherwise noted. RESULTS AND DISCUSSION
Feed Analysis
Composition of sunflower and safflower seeds are given in Table 2. Sunflower seeds
1939
UNSATURATED DIETARY FAT AND SOMATOTROPIN
TABLE 3. Composition of concentrate mixes, forages, and TMR from control (C), control with bST (C+), dietary fat from sunflower seed with bST (Sun+), and dietary fat from safflower seed with bST (Saff+) treatments. Concemte mix
TMRl
Measurement
candc+
sun+
saff+
Corn silage
Alfalfa hay
candc+
sun+
saff+
DM, %
89.3
90.6
90.8
40.9
83.7
75.8
76.5
76.6
19.2 2.3 25.8 15.5 2.8 8.8 1.42 .45 .40 1.61
19.4 6.2 27.2 17.1 3.1 8.8 1.27 .45 .42 1.72
19.5 5.5 28.7 17.9 2.9 9.0 1.34 .43 .42
(% of DM)
CP Ether extract NDF ADF Lignin Ash
Ca P Mg
24,l 2.1 11.7 4.9 1.5 9.6 1.88 .63 .51
24.5 9.9 14.5 8.2 2. I 9.5 1.59 .65 .60
24.8 8.5 17.4 9.7 1.7 9.9 1.72 .60 .54
McaVkg
8.8 2.8 40.2 23.3 2.6 5.4 .27 25 28
19.0 2.1 39.7 28.8 5.6 10.8 . 1.65 .26 .31
1.72
'Calculated at ratio of 50:25:25, concentrate mix, corn silage, alfalfa hay, respectively. 'Estimated.
contained slightly greater quantities of CP, ether extract, ash, and total fatty acids than safflower seeds. Composition for safflower seeds was similar to that listed in NRC (14) except for ether extract, which was higher (6.4 percentage units) than in the NRC listing. Safflower seeds contained greater quantities of NDF and ADF than sunflower seeds. Sunflower seeds are not listed in NRC (14) but were similar in composition to those obtained in other studies (5, 11). Safflower seeds contained greater quantities of c18:2 and lesser quantities of other fatty acids, especially C1g.o and C1g.1, than sunflower seeds. Linoleic acid was the predominant fatty acid in both oilseeds; safflower seeds contained greater than 80% C1g.2 in total fatty acids. The composition of concentrate mixtures, forages, and calculated TMR are given in Table 3. Concentrate mixtures and TMR contained slightly greater than 24 and 19% CP, which exceeded initial dietary formulations. The TMR were formulated at 19% CP to supply additional protein and AA for milk protein synthesis to offset a possible reduction in postruminal A A supply when fat was added to the diet. Ether extract concentrations were increased for the Sun+ and Saff+ concentrate mixtures and TMR compared with the C concentrate mixture and TMR because of the 20% substitution of rolled sunflower and safflower seeds
(Table 3). The inclusion of sunflower and safflower seeds in the concentrate mixture provided approximately 3.9 and 3.2 percentage units of additional fat in the diet. This additional fat was predominantly C1g.2 (Table 2), which resulted in 1.92 and 1.91 percentage units more C18:~in the diet (Table 4). Total dietary fatly acid concentrations were 3.22 and 2.58 percentage units higher for Sun+ and Saff+ treatments, respectively, than for the C treatment (Table 4). Dietary total fatty acid concentrations (Table 4) were lower (nonsignificantly) than dietary ether extract concentrations (Table 3) for Sun+ and Sa€f+ treatments. In contrast, dietary total fatty acid concentrations for the C and C+ treatments were greater than for the dietary ether extract concentrations. Differences in results between the two fat analysis procedures (i.e., ether extract vs. total fatty acids) were within normal standard errors. The fatty acid analysis procedure (23) is probably the most accurate and is the recommended procedure. Concentrations of NDF, ADF, and lignin were higher in Sun+ and Saff+ diets (Table 3), reflecting the higher fiber content of those seeds. But fiber was lower in the corn silage than NRC values (14), which caused all diets to contain less fiber than anticipated. Ash, Ca, P, and Mg concentrations were adequate and similar for a l l diets. Limestone was added to the concentrate mixtures (Table 1) to increase Journal of Dairy Science Vol. 75. No. 7, 1992
1940
STEGEMAN ET AL.
TABLE 4. Patty acid composition of concentrate mixes,forages, and TMR from control (0, control with bST (C+), dietary fat from sunflower seed with bST (Sun+), and dietary fat from safflower seed with bST (Sa+) treatments. Concentrate mix Sun+
saff+
.02
.02
.89 .16 .03 55 2.11 5.49 .12 .05 .13 -07
.89 29 .31 1.08 5.47 .12
.02
.02
.07 9.70
.05
Fatty acid'
C and C+
140 16:O 1 61 17:O 18:O 18:1 18:2 18:3 200 201 22:o 22: 1
.01 .38 .26 .03 .08 .66 1.66 .12 .01 .a2 .01 -03 .01 3.26
24:O
Total
.04
.04 .08 .03
8.41
.01 .35 .04 .13 .06 .7 1 .90
TMR2
Alfalfa
COnn silage
C d C +
bY
(% of DM) .03
.o 1 .38 .16 .13
.40 .08 .33 .08 .08 23 .30
.ll
.16 .o 1 .01 co1 .03 253
.02 .13 .31 1.26 3.03 .16 .07 .12
.02 .63 .17 .14 .I9 .74 3.02 .16 .07 .10
.04
.M
.01 .05 5.93
.01
.ll
53 1.11 .16 .05 .o 1 .01 .02 .02 2.66
.2 1 .02 .01 .03 1.81
Sa+
.63
.07
.02
sun+
.04 5.29
lFixpmsed as number of carbomnumber of double bonds. kalculated as ratios of 502525, ccmcentrate mix, corn silage, and alfalfa hay, respectively.
Ca concentrations to 1%of dietary DM, how- know why. Body weights and BW gains were ever, Ca concentrations were much greater similar (P > .lo) for all treatments. than 1%of dietary DM because of a greater Ca content of alfalfa hay than anticipated (1.65 vs. Mllk Yleld 1.25%). Magnesium concentrations were inAdministration of 15.5 mg of bST/d per creased by addition of MgO to assist in formacow to midlactation cows (C+)nonsignifition of Mg soaps. Calcium and Mg were increased in the diet because added fat increases cantly increased the yields of milk, 4% FCM, Ca and Mg soap formation in the rumen and and SCM by 10.8, 11.5, and 12.6%, respecincreases the excretion of these elements in the tively, compared with the C treatment (Table 5). Milk yield (P < .lo) increased because of feces (14, 15). the inclusion of added fat, but most of this DMI and BW
Dry matter intakes were not influenced by administration of bST or by feeding the Sun+ treatment (Table 5). However, DMI was lower for the Saff+ than for the Sun+ treatment. Previous long-term studies with M T reported similar or increased DMI (6, 7). Dry matter intake is usually not reduced until fat content of the diet exceeds 8% of DMI (5, 11, 15). Cows fed the S a + treatment had lower DMI than cows in other experimental treatments throughout the experimental period (Figure 1). Reductions in DMI for the Saff+ treatment
Journal of Dairy Science Vol. 75, No. 7. 1992
n
32 28 1
CT)
> _I
24
D 20 16
I
4
7
IO
Experimental Week
13
16
1941
UNSATURATED DIETARY FAT AND SOMATOTROPJN
TABLE 5. Dry matter intake, BW, and milk yield and composition from contml (C),control with bST (C+), diem fat from sunflower seed with bST (Sun+), and dietary fat from safflower seed with bST (Saff+) treatments. contrasts,' P 2 3
,rmummt C
C+
Slm+
275 613 4.55 24.7 295 25.0 25.3 2.99 3.17 4.87 8.74 .70
23.9 624 3.83 19.4 32.7 27.9 285 3.06 327 4.82 8.83 .70
27.3 663 4.11 36.1 40.0 32.3 32.9 2.73 3.02 4.95 8.68 .70
2.0 SE
M+
19.3
607
1 .22
3.18 39.9 34.1 28.1 28.6 286 3.08 4.84 8.62 .71
.19 .77 20 .17 .16 .73 28 55
.M
.46 .%
.08
.01
.a2 .ll .lo
.82 55 .68 23 .06 .18 .21 .13 .02 .30 .12 .73
.70
23 .36 12.3 1.6 1.3 1.4 .13 .06
.83 .02 .04 .04 .49 59 .12 58 .65
k o n m t s : 1 = c versus c+, 2 = C+ versus sun+ and s&+, and 3 = sun+ verms s&+. kovariate adjusted. %CM = (kilograms of milk x .4)+ (kilograms of milk fat x 15). %CM = [kilograms of milk x (.0752)] + (kilograms of milk fat x 12.3) + (kilograms of milk SNF x 656).
increase occurred with the Sun+ treatment. However, yields of 4% FCM and S C M were not increased, because of slight reductions in fat and protein concentrations by feeding high fat diets. Yields of milk, 4% FCM, and SCM were greater for the Sun+ than for the Saff+ treatments, which can be attributed to the lower DMI for the Saff+ treatment. Cows on the C+ treatment consistently yielded more milk throughout the experimental period than the controls (Figure 2). Addition of fat to the diet (the Sun+ and S a + treatments) further enhanced milk yield consistently throughout the experimental perid, the greatest milk response was for the Sun+ treatment. Cows fed diets containing added fat had a greater energetic efficiency (17), which could support the greater milk yield with less DMI of the Saff+ compared with the C+ treatment. Several studies (2, 6,7)evaluating the efficacy of bST administration have observed yield responses with bST that were similar to results obtained in this study. Feeding 3 to 5% additional fat in the diet via whole oilseeds increased milk yield in several studies (15, 17). Previous studies (2) also observed an additive effect of bST and supplemental fat on milk yield. To our howledge, no studies to date have compared feeding safflower seeds to dajl cows with feeding other oilseeds.
Milk Fat
Percentages of milk fat were similar (P > .lo) for all treatments (Table 5). Feeding oilseeds, which are high in polyunsaturated fatty acids and unprotected from the ruminal environment, decreased milk fat percentages in some studies (5, 15), but not in others (11, 12, 15,17). Administration of bST increased milk fat content in short-term studies (16), but longterm studies showed no differences (6, 7).
6.0 41.0
-0
\
0) 37.0
Y Y = n.0 2
290
25.04 0
!
I
I
I
4
I
I
I
I
I
~
I
I
Experirnintal Week j2
;
I
I
I
16
Figure 2. Covariate-adjusted milk yield for cows fed conml (C) (.) or rec+iVing bST and fed control (+), sunflower seed (e), or safflower seed @) diets.
Journal of Dahy Science Vol. 75, No. 7. 1992
1942
STEGEMAN ET AL.
TABLE 6. Fatty acid composition of milk fat from catto1 (0, control with bST (C+), dietary fat from sunflower seed with bST (Sun+), and dietary fat from safflowex seed with bST ( S a + ) treatments.
Contrasts,' P
Treatment Fatty acid2
40 60 8:O
100 120 140 141 15:o 15:l 160 16 1 17:O 171 18:O 18:1 Cis- 18:1 Trm-18:1 18:2 SCFA3 MOA3 LOA3 sat3 UnSd
C
C+
4.0 2.8 1.7 4.1 4.7 13.1 1.7 1.4 .4 31.6 25 .6 .3 8.1 18.0 15.8 1.8 2.0 17.2 50.7 29.1 72.1 25.O
w100 B) 3.7 2.1 1.1 2.2 2.4 92 1.1 .7 .3 20.8 2.1 .4 .4 .3 8.3 14.9 20.7 325 18.5 282 1.8 3.8 2.2 3.3 16.3 11.7 48.1 34.3 322 51.4 68.2 57.8 28 4 39.6
Sun+
3.9 2.7 1.6 3.8 4.4 122 1.9 1.3 .3 29.5 2.9 .6
saff+
SE
1
2
3
4.2 2.4 1.3 2.5 2.7 9.5 1.3
.1
Feeding unsaturated dietary fat to lactating dairy cows receiving bST may effectively alter the fatty acid composition of milk fat. This was tested using 16 Holstein cows assigned to one of four treatments during midlactation. Treatments were control, control diet with 15.5 mg of bST/d per cow, dietary fat from sunflower seeds and bST, or dietary fat from safflower seeds and bST. Diets were formulated to contain 19%CP and contained 25% corn silage, 25% alfalfa hay, and 50% concentrate mix on a DM basis. Milk yield was not significantly higher when bST was administered and increased with added fat diets (29.5, 32.7,40.0, and 34.1 kg/d for the control, control with bST, d o w e r seed with bST, and safflower seed with bST treatments, respectively). Percentage of milk fat was similar for all treatments. Concentrations of long-chain and unsaturated fatty acids in milk were increased slightly by bST and substantially with added fat. Milk protein percentages were not influenced by bST but were reduced by approximately .2 unit with added fat. Added unsaturated dietary fat coupled with bST increased milk yield and produced a greater concentration of unsaturated fatty acids in milk. (Key words: unsaturated fatty acids, milk, bovine somatotropin)
Abbreviation key: C = control, C+ = control with bST, Saff+ = dietary fat from safflower seeds with bST, Sun+ = dietary fat from sunflower seeds with bST. INTRODUCTION
Consumers today are more health conscious and are demanding dairy products lower in milk fat, especially saturated fat. Presently, reductions 'in milk fat concentrations through nutritional modification are not feasible for the long-term health of the dairy cow. However, increasing the unsaturated fatty acid composition of milk fat is possible (3, 5). Manufacturing this milk into dairy products may offer a potential market for the dairy industry (3). Dietary manipulation is one of several methods to alter the fatty acid composition of milk Recent studies demonstrated that milk fat from dairy cows fed diets containing soybeans (12) or sunflower seeds (5, 17) contained greater concentrations of unsaturated fatty acids than that of cows fed diets without supplemental fat. Dairy producers may be able to customize the fatty acid profile of milk fat for dairy products by varying the fatty acid distribution of dietary fat fed to cows (3, 5). Many bST studies have shown increased milk yield (2, 16), but few studies have detailed data on the distributions of fat and protein fractions in milk from cows during long-term studies. In a short-term study, Eppard et al. (9) reported that, as dose of bST increased, the concentration of unsaturated fatty acids in milk fat increased. Baer et aL (4) Received October 25, 1991. reported that cows receiving 30.9 mg of bST/d Accepted March 2,1992. 'PUW with ~IXapproval of the director of the per cow in a long-term study had milk fat and South D h t a Agricultuxal Experiment Station as Publica- protein percentages similar to those of cows tion Number 2584 of the Journal Series. not receiving bST, but fatty acid and protein 'Present address: Ruminant Nutrition Laboratory, fractions were altered. Milk fat contained USDA-ARS, Building 162, Beltsville Agricaltural Regreater concentrations of long-chain and unsatsearch Center-East, Beltsville, MD 20705-2350. urated fatty acids, whereas casein as a percenth p r i n t requests. 1992 J Dairy Sci 75:1936-1945
1936
UNSATURATED DIETARY FAT AND SOMATOTROPIN
1937
age of total and true protein was lower for TABLE 1. Ingredient content of concentrate mixtures.' cows receiving bST. These changes in fat and protein were more pronounced in the first 6 wk C of WT administration when cows appeared to Insrrdient andC+ Sun+ Saff+ be in negative energy and protein balance. (% as mixed) Changes in the fatty acid composition of 492 34.0 32.9 Com, g r o u n d and shelled milk fat because of changes in ration composi34.5 35.6 Soybean meal, 44% 8 39.3 tion and administration of bST may be additive sllnflower seeds, rolled . . . 20.0 ... (3). New technologies may allow formulation safflower d, ... . . . 20.0 rolled 5 .o 5.0 5.0 of diets to alter the fatty acid composition of Liquid molasses 2.5 2.5 2.5 milk fat to meet the recommendations of many Limestone 1.0 1.o 1.0 Dicalcium phosphate human health professionals for reduced intake 1.o 1.0 1.0 Tracamingalized salt3 of saturated fats. The objective of this study Sodium bicarbonate 15 1.5 1.5 was to utilize available feed sources and tech- Magnesium oxide 5 .5 5 nologies to alter the fatty acid composition of 'Also added were 8818 IU of vitamin A, 1764 IU of milk fat. vitamin D, and 45 IU of vitamin E/Lg of mixtures.
-
MATERIALS AND METHODS
Sixteen Holstein cows (4 primiparous) in midlactation (75 to 173 DIM, average 104) were blocked by milk yield and parity and assigned randomly to one of four treatments. Treatments were control (C) diet containing corn and soybean meal as the main ingredients in the concentrate mix, C diet with 15.5 mg of bST/d per cow (C+),dietary fat from sunflower seeds with bST (Sun+), and dietary fat from safflower seeds with bST (Saff+). Injections of WT (American Cyanamid, Princeton, NJ) were administered subcutaneously at lo00 h daily in the pocket lateral to the tailhead, alternating sides daily, using 20-mm, 20-gauge needles. The 4 C treatment cows received 1 ml of sterile buffered saline daily. Total mixed diets were formulated (DM basis) to be isonitrogenous (19% CP) and consisted of 25% corn silage, 25% chopped alfalfa hay, and 50% of the respective concentrate mixtures. Rolled sunflower and safflower seeds were included at 20% of the concentrate mixture to replace portions of corn and soybean meal (Table 1). Sunflower and safflower seeds were chosen and because of their high fat content (M%) variation in fatty acid composition [>65 and >8O% linoleic acid (c18:2), respectively; Table 21. Limestone and MgO were included in the concentrate mixture to supply additional Ca and Mg to minimize alterations in rumen fermentation because of high fat diets (15). The experiment was divided into three periods. Period l (pretreatment) was l wk (wk 11 postpartum), during which all cows were fed
-
k = Control, C+ = control with bST, Sun+ = dietary fat from sunflower seeds with bST, and Saff+ = dietary fat from safflower seeds with bST. 3Cmtained (46): NaCl (97 to 98.5), I (.007), M n (M), Fe (m), Mg (.050), CU (.032), Co (.Oil), Zn
(.ow.
the herd ration; milk yield and composition data were collected to be used as covariates. Period 2 was the next 4 wk, when cows were allowed to adapt to the respective treatment diets. Period 3 was the 16wk experimental period, commencing with the daily injections of bST and collection of data. Cows were housed in a free-stall barn, and diets were fed once daily for ad libitum intake using Calan feeding doors (American Calan, Inc., Northwood, NH); amounts of feed fed and refused were recorded daily. Body weights were recorded during 3 consecutive d at the start of the experiment, then weekly, and on 3 consecutive d at the end of the experimental
period. Corn silage, alfalfa hay, and concentrate mixtures were sampled weekly throughout the experiment and frozen. Samples were combmed into monthly composites, dried at 5YC, and ground through an ultracentrifuge mill with a 1-mm screen (Brinkman Instruments Co., Westbury, NY). Dry matter, CP, ether extract, ash in feed samples and oilseeds, and Ca, P, and Mg in feed samples were analyzed according to the procedures of AOAC (1). Neutral detergent fiber, ADF, and permanganate lignin were determined by the proceJournal of Dairy Science Vol. 75, No. 7, 1992
1938
STEGEMAN ET AL.
TABLE2. Composition of sunflowerand safflowerseeds. Measurement
DM, % cp MIF
ADF Ether extract Ash
smower
Sunflower 94.3
-(%
Of
94.4
DM)
20.6 24.1 17.4 42.6 3.5
-
185 34.6 24.7 41 5 25
Fatty acid composition 140' .a2 16:O 2.66 16:l .I6 ... 17:O 18:O 1.92 8.68 18:1 18:2 29.13 .24 18:3 20 1 .88 22:o .38 .03 22: 1 24:O .23 Total fatty acids 44.33
.052 6.00 .36
.OS
2.83 .06
.29 4.33 19.58 65.71 .54 1.99 .86
.07 .51
.80
3.78 33.97 .10 .18
.I22 6.69 .14 .69 1.89 8.94 80.33
.09
.01 .13 42.29
24 .43 .21
.m
.31
~~
'Expressed as number of carb0nS:number of double bonds. 2 ~ are expressed ~ ~ as grams m per 100 g of total fatty acids.
milk fat content in the present study is based on the Mojonnier ether extraction -procedure (22). Milk samples were analyzed for fatty acid composition by GLC separation of butyl esters (5). Nitrogen distributions were determined by the Rowland method (19), and the individual milk protein fractions were separated by electrophoresis using a gradient SDSPAGE system (13). Samples of ruminal fluid were taken four times during the experiment, approximately once every 4 wk. Two to 4 h after feeding, samples were collected via an esophageal tube into bottles containing .5 ml of saturated HgCl2. Samples were analyzed for pH, fitered through four layers of cheesecloth, and prepared for VFA and ruminal ammonia determinations (5). Samples of jugular vein blood were drawn into serum separation tubes at the time of rumen sampling. They were centrifuged for 20 min at 850 x g, and the Supernatant fractions were decanted and frozen at -2o'C. Jugular serum samples were analyzed for urea N concentration (5). Statlsticai Analysis
dures of Robertson and Van Soest (18). Fatty acid content in feed samples and oilseeds was determined as described by Sukhija and Palmquist (23). Cows were milked twice daily; milk weights were recorded at each milking throughout the experimental period. Two 24-h (a.m. and p.m.) milk samples were collected from each cow during the prematment week. One 24-h (a.m. plus p.m.) milk sample was collected each week throughout the experimental period. Samples were analyzed for milk fat, protein, SNF, and lactose by midinfiared spectrophotometry (Multispec, Foss Food Technology Corp., Eden Prairie, MN) according to AOAC procedures (1). This method uses two filters (A and B) with corresponding wavelengths of 5.73 pm and 3.4 to 3.5 pm. A companion study (22) was conducted to evaluate different methods of milk fat determination. Results indicated that the midinfrared spectroscopic method underestimated milk fat content when the concentration of unsaturated fatty acids was high. Therefore, Journal of Dairy Science Vol. 75, No. 7, 1992
Milk yield and composition data were adjusted by analysis of covariance (21) using milk yield and composition data collected during the pretreatment period as covariates. All data were subjected to least squares ANOVA for a split-plot design; the main plot was arranged in a randomized complete block design with week of experiment as the subplot (21) and analyzed by the general linear models procedure (20). Results are expressed as least squares means. Sources of variation were covariate, replication, treatment, experimental week, and the interaction of treatment by experimental week. Contrasts of 1) C versus C+, 2) C+ versus Sun+ and Sa+, and 3) Sun+ versus Saff+ were used to separate treatment effects in the main plot (21). Significance was declared at P < .05 unless otherwise noted. RESULTS AND DISCUSSION
Feed Analysis
Composition of sunflower and safflower seeds are given in Table 2. Sunflower seeds
1939
UNSATURATED DIETARY FAT AND SOMATOTROPIN
TABLE 3. Composition of concentrate mixes, forages, and TMR from control (C), control with bST (C+), dietary fat from sunflower seed with bST (Sun+), and dietary fat from safflower seed with bST (Saff+) treatments. Concemte mix
TMRl
Measurement
candc+
sun+
saff+
Corn silage
Alfalfa hay
candc+
sun+
saff+
DM, %
89.3
90.6
90.8
40.9
83.7
75.8
76.5
76.6
19.2 2.3 25.8 15.5 2.8 8.8 1.42 .45 .40 1.61
19.4 6.2 27.2 17.1 3.1 8.8 1.27 .45 .42 1.72
19.5 5.5 28.7 17.9 2.9 9.0 1.34 .43 .42
(% of DM)
CP Ether extract NDF ADF Lignin Ash
Ca P Mg
24,l 2.1 11.7 4.9 1.5 9.6 1.88 .63 .51
24.5 9.9 14.5 8.2 2. I 9.5 1.59 .65 .60
24.8 8.5 17.4 9.7 1.7 9.9 1.72 .60 .54
McaVkg
8.8 2.8 40.2 23.3 2.6 5.4 .27 25 28
19.0 2.1 39.7 28.8 5.6 10.8 . 1.65 .26 .31
1.72
'Calculated at ratio of 50:25:25, concentrate mix, corn silage, alfalfa hay, respectively. 'Estimated.
contained slightly greater quantities of CP, ether extract, ash, and total fatty acids than safflower seeds. Composition for safflower seeds was similar to that listed in NRC (14) except for ether extract, which was higher (6.4 percentage units) than in the NRC listing. Safflower seeds contained greater quantities of NDF and ADF than sunflower seeds. Sunflower seeds are not listed in NRC (14) but were similar in composition to those obtained in other studies (5, 11). Safflower seeds contained greater quantities of c18:2 and lesser quantities of other fatty acids, especially C1g.o and C1g.1, than sunflower seeds. Linoleic acid was the predominant fatty acid in both oilseeds; safflower seeds contained greater than 80% C1g.2 in total fatty acids. The composition of concentrate mixtures, forages, and calculated TMR are given in Table 3. Concentrate mixtures and TMR contained slightly greater than 24 and 19% CP, which exceeded initial dietary formulations. The TMR were formulated at 19% CP to supply additional protein and AA for milk protein synthesis to offset a possible reduction in postruminal A A supply when fat was added to the diet. Ether extract concentrations were increased for the Sun+ and Saff+ concentrate mixtures and TMR compared with the C concentrate mixture and TMR because of the 20% substitution of rolled sunflower and safflower seeds
(Table 3). The inclusion of sunflower and safflower seeds in the concentrate mixture provided approximately 3.9 and 3.2 percentage units of additional fat in the diet. This additional fat was predominantly C1g.2 (Table 2), which resulted in 1.92 and 1.91 percentage units more C18:~in the diet (Table 4). Total dietary fatly acid concentrations were 3.22 and 2.58 percentage units higher for Sun+ and Saff+ treatments, respectively, than for the C treatment (Table 4). Dietary total fatty acid concentrations (Table 4) were lower (nonsignificantly) than dietary ether extract concentrations (Table 3) for Sun+ and Sa€f+ treatments. In contrast, dietary total fatty acid concentrations for the C and C+ treatments were greater than for the dietary ether extract concentrations. Differences in results between the two fat analysis procedures (i.e., ether extract vs. total fatty acids) were within normal standard errors. The fatty acid analysis procedure (23) is probably the most accurate and is the recommended procedure. Concentrations of NDF, ADF, and lignin were higher in Sun+ and Saff+ diets (Table 3), reflecting the higher fiber content of those seeds. But fiber was lower in the corn silage than NRC values (14), which caused all diets to contain less fiber than anticipated. Ash, Ca, P, and Mg concentrations were adequate and similar for a l l diets. Limestone was added to the concentrate mixtures (Table 1) to increase Journal of Dairy Science Vol. 75. No. 7, 1992
1940
STEGEMAN ET AL.
TABLE 4. Patty acid composition of concentrate mixes,forages, and TMR from control (0, control with bST (C+), dietary fat from sunflower seed with bST (Sun+), and dietary fat from safflower seed with bST (Sa+) treatments. Concentrate mix Sun+
saff+
.02
.02
.89 .16 .03 55 2.11 5.49 .12 .05 .13 -07
.89 29 .31 1.08 5.47 .12
.02
.02
.07 9.70
.05
Fatty acid'
C and C+
140 16:O 1 61 17:O 18:O 18:1 18:2 18:3 200 201 22:o 22: 1
.01 .38 .26 .03 .08 .66 1.66 .12 .01 .a2 .01 -03 .01 3.26
24:O
Total
.04
.04 .08 .03
8.41
.01 .35 .04 .13 .06 .7 1 .90
TMR2
Alfalfa
COnn silage
C d C +
bY
(% of DM) .03
.o 1 .38 .16 .13
.40 .08 .33 .08 .08 23 .30
.ll
.16 .o 1 .01 co1 .03 253
.02 .13 .31 1.26 3.03 .16 .07 .12
.02 .63 .17 .14 .I9 .74 3.02 .16 .07 .10
.04
.M
.01 .05 5.93
.01
.ll
53 1.11 .16 .05 .o 1 .01 .02 .02 2.66
.2 1 .02 .01 .03 1.81
Sa+
.63
.07
.02
sun+
.04 5.29
lFixpmsed as number of carbomnumber of double bonds. kalculated as ratios of 502525, ccmcentrate mix, corn silage, and alfalfa hay, respectively.
Ca concentrations to 1%of dietary DM, how- know why. Body weights and BW gains were ever, Ca concentrations were much greater similar (P > .lo) for all treatments. than 1%of dietary DM because of a greater Ca content of alfalfa hay than anticipated (1.65 vs. Mllk Yleld 1.25%). Magnesium concentrations were inAdministration of 15.5 mg of bST/d per creased by addition of MgO to assist in formacow to midlactation cows (C+)nonsignifition of Mg soaps. Calcium and Mg were increased in the diet because added fat increases cantly increased the yields of milk, 4% FCM, Ca and Mg soap formation in the rumen and and SCM by 10.8, 11.5, and 12.6%, respecincreases the excretion of these elements in the tively, compared with the C treatment (Table 5). Milk yield (P < .lo) increased because of feces (14, 15). the inclusion of added fat, but most of this DMI and BW
Dry matter intakes were not influenced by administration of bST or by feeding the Sun+ treatment (Table 5). However, DMI was lower for the Saff+ than for the Sun+ treatment. Previous long-term studies with M T reported similar or increased DMI (6, 7). Dry matter intake is usually not reduced until fat content of the diet exceeds 8% of DMI (5, 11, 15). Cows fed the S a + treatment had lower DMI than cows in other experimental treatments throughout the experimental period (Figure 1). Reductions in DMI for the Saff+ treatment
Journal of Dairy Science Vol. 75, No. 7. 1992
n
32 28 1
CT)
> _I
24
D 20 16
I
4
7
IO
Experimental Week
13
16
1941
UNSATURATED DIETARY FAT AND SOMATOTROPJN
TABLE 5. Dry matter intake, BW, and milk yield and composition from contml (C),control with bST (C+), diem fat from sunflower seed with bST (Sun+), and dietary fat from safflower seed with bST (Saff+) treatments. contrasts,' P 2 3
,rmummt C
C+
Slm+
275 613 4.55 24.7 295 25.0 25.3 2.99 3.17 4.87 8.74 .70
23.9 624 3.83 19.4 32.7 27.9 285 3.06 327 4.82 8.83 .70
27.3 663 4.11 36.1 40.0 32.3 32.9 2.73 3.02 4.95 8.68 .70
2.0 SE
M+
19.3
607
1 .22
3.18 39.9 34.1 28.1 28.6 286 3.08 4.84 8.62 .71
.19 .77 20 .17 .16 .73 28 55
.M
.46 .%
.08
.01
.a2 .ll .lo
.82 55 .68 23 .06 .18 .21 .13 .02 .30 .12 .73
.70
23 .36 12.3 1.6 1.3 1.4 .13 .06
.83 .02 .04 .04 .49 59 .12 58 .65
k o n m t s : 1 = c versus c+, 2 = C+ versus sun+ and s&+, and 3 = sun+ verms s&+. kovariate adjusted. %CM = (kilograms of milk x .4)+ (kilograms of milk fat x 15). %CM = [kilograms of milk x (.0752)] + (kilograms of milk fat x 12.3) + (kilograms of milk SNF x 656).
increase occurred with the Sun+ treatment. However, yields of 4% FCM and S C M were not increased, because of slight reductions in fat and protein concentrations by feeding high fat diets. Yields of milk, 4% FCM, and SCM were greater for the Sun+ than for the Saff+ treatments, which can be attributed to the lower DMI for the Saff+ treatment. Cows on the C+ treatment consistently yielded more milk throughout the experimental period than the controls (Figure 2). Addition of fat to the diet (the Sun+ and S a + treatments) further enhanced milk yield consistently throughout the experimental perid, the greatest milk response was for the Sun+ treatment. Cows fed diets containing added fat had a greater energetic efficiency (17), which could support the greater milk yield with less DMI of the Saff+ compared with the C+ treatment. Several studies (2, 6,7)evaluating the efficacy of bST administration have observed yield responses with bST that were similar to results obtained in this study. Feeding 3 to 5% additional fat in the diet via whole oilseeds increased milk yield in several studies (15, 17). Previous studies (2) also observed an additive effect of bST and supplemental fat on milk yield. To our howledge, no studies to date have compared feeding safflower seeds to dajl cows with feeding other oilseeds.
Milk Fat
Percentages of milk fat were similar (P > .lo) for all treatments (Table 5). Feeding oilseeds, which are high in polyunsaturated fatty acids and unprotected from the ruminal environment, decreased milk fat percentages in some studies (5, 15), but not in others (11, 12, 15,17). Administration of bST increased milk fat content in short-term studies (16), but longterm studies showed no differences (6, 7).
6.0 41.0
-0
\
0) 37.0
Y Y = n.0 2
290
25.04 0
!
I
I
I
4
I
I
I
I
I
~
I
I
Experirnintal Week j2
;
I
I
I
16
Figure 2. Covariate-adjusted milk yield for cows fed conml (C) (.) or rec+iVing bST and fed control (+), sunflower seed (e), or safflower seed @) diets.
Journal of Dahy Science Vol. 75, No. 7. 1992
1942
STEGEMAN ET AL.
TABLE 6. Fatty acid composition of milk fat from catto1 (0, control with bST (C+), dietary fat from sunflower seed with bST (Sun+), and dietary fat from safflowex seed with bST ( S a + ) treatments.
Contrasts,' P
Treatment Fatty acid2
40 60 8:O
100 120 140 141 15:o 15:l 160 16 1 17:O 171 18:O 18:1 Cis- 18:1 Trm-18:1 18:2 SCFA3 MOA3 LOA3 sat3 UnSd
C
C+
4.0 2.8 1.7 4.1 4.7 13.1 1.7 1.4 .4 31.6 25 .6 .3 8.1 18.0 15.8 1.8 2.0 17.2 50.7 29.1 72.1 25.O
w100 B) 3.7 2.1 1.1 2.2 2.4 92 1.1 .7 .3 20.8 2.1 .4 .4 .3 8.3 14.9 20.7 325 18.5 282 1.8 3.8 2.2 3.3 16.3 11.7 48.1 34.3 322 51.4 68.2 57.8 28 4 39.6
Sun+
3.9 2.7 1.6 3.8 4.4 122 1.9 1.3 .3 29.5 2.9 .6
saff+
SE
1
2
3
4.2 2.4 1.3 2.5 2.7 9.5 1.3
.1
