Influence of Bovine Somatotropin and Nutrition on Production and Composition of Milk from Dairy Cows' CHRISTOPHER L. AUSTIN, DAVID J. SCHINGOETHE, and DAVID P. CASPER~ Dairy Science Department South Dakota State University Brookings 57007 RALPH M. CLEALE American Cyanamid Company Princeton, NJ 08540

Dry matter intake was not significantly elevated by bST (23.1 vs. 22.8 kg/d) but was lower for high protein and energy (22.0 vs. 23.8 kg/d). Increased dietary protein and energy with bST augmented the total milk production response. (Key words: somatotropin, dietary protein, dietary fat)

ABSTRACT

Forty-eight multiparous Holstein cows were used in an experiment with a 2 x 2 factorial arrangement of treatments to study interactions of bST and nutrient density during wk 5 through 20 postpartum. Main effects were bST (0 or 10.3 mg/d) and diet (control or high protein and energy). The control diet was formulated to contain 16.3% CP and 1.65 Mcal of NE&g of DM; the high protein and energy diet was formulated to contain 18% CP and 1.74 Mcal of NE&g of DM with additional energy as fat from extruded soybeans and calcium salts of fatty acids. Diet ratios were 50:25:25 for concentrate:alfalfa hay:com silage (DM basis). Bovine somatotropin increased milk production (40.9 vs. 37.9 kg/d) and production of 4% FCM (35.7 vs. 32.3 kg/d). The high protein and energy diet increased milk production (40.3 vs. 38.5 kg/d); 4% F C M production was higher for high protein and energy plus bST (36.0 kg) than without bST (33.6 kg). Percentage of milk fat was not affected by treatment. Percentage of milk protein was reduced with the high protein and energy diet, presumably because of the added fat, but this reduction was less with high protein and energy plus bST.

Abbreviation key: C = controk Ca-LCFA = Ca salts of long-chain fatty acids; ESB = extruded soybeans; HPE = high protein and energy; LCFA = long-chain fatty acids; MCFA = medium-chain fatty acids; SCFA = short-chain fatty acids; - = without bST, + = with 10.3 mg/d of bST. INTRODUCTION

Received April 18, 1991. Accepted July 29, 1991. 'Published with the approval of the director of the South Dakota Agricultural Experiment Station as Publication Number 2556 of the Journal Series. 'Resent address: Ruminant Nutrition Laboratory, USDA, ARS, Beltsville, MD 20705. 1991 J Dairy Sci 743920-3932

Dairy cows treated with bST usually respond with a 2 to 5 kg/d increase in milk production (4, 11, 26, 28). Changes in milk composition when cows are treated with bST usually are minimal and reflect the nutritional status of the cow (18). Energy deficiency usually has resulted in increased milk fat content (12). When cows were in a negative N balance, casein (2) and total protein (4) were reduced for bST-treated cows. Evidence has been presented indicating that the bST-treated cow is similar to the genetically superior cow (18) in many physiological aspects related to high milk production. Thus, the bST-treated cow should be fed according to current recommendations for high production. However, when miLk production increases, traditional diets may lack sufficient protein and energy (8, 16). Protein and energy densities of diets need to be increased in early lactation, and increased amounts of undegradable protein may be necessary for optimal energy utilization.

3920

3921

SOMATOTROI" AND NUTRITION

Feeding supplemental fat during early lacta- TABLE 1. Ingredient content of control (C) and high tion to increase dietary energy density has protein and energy (HPE) diets. improved milk production (17); however, Diet' depression of milk protein concentration is Lneredient C HPE common when diets are supplemented with fat (% Of DM) (517). This may be due to reduced AA uptake 25.00 25.00 Alfalfa hay, chopped by the mammary gland, which may result from 25.00 25.00 Corn silage hormonal changes induced by dietary fat (5). Corn, ground shelled 33.75 23.90 Elevated plasma fatty acid concentrations may Soybean meal, 44% CP 14.15 10.20 .., 11.20 inhibit somatotropin release from the anterior Extruded soybeans ... 2.60 pituitary. It has been proposed recently that Megalaca .70 70 phosphate exogenous bST may alleviate milk protein Dicalcium .60 .60 SOdiUUI bicarbonate depression (5) that occurs when cows are fed Trace-mineralized salt .40 .40 .20 .20 added fat. Limestone .20 20 The objective of this study was to measure Uagnesium oxide 100.00 100.00 the milk production responses to bST in dairy Total cows fed either a typical diet formulated for 'Plus 4400 IU of vitamin A, 880 IU of vitamin D, and high producing cows or a diet containing sup- .44 IU of vitamin E& of DM. plemental protein and energy. Particular attention was given to milk protein concentration in order to test the proposed mechanism (5) to alleviate milk protein depression for cows fed produce 40.9 kgJd of milk containing 3.5% added fat. milk fat when consuming 21.3 kg of DM daily. Protein and energy were increased by partial MATERIALS AND METHODS replacement of corn and soybean meal with equal amounts of supplemental fat from exForty-eight multiparous Holstein cows were truded soybeans (ESB) (Trip,e Feeds, Des used in a 16-wk lactation experiment with a 2 Moines, IA) and Ca salts of long-chain fatty Of in a acids (Ca-LCFA) (Megalac@, Church and randomized complete block design. Treatments involved two diets, control (C) and high pro- Dwight Co., Princeton, NJ). Calcium was intein and energy (HPE), with (+) or without (-) creased to more than .9% of DM in the HPE diet, as is recommended with high fat diets mg/d Of bST Princeton, NJ). Cows were blocked (replicate) (16). Ratios were 502525 for concentrate: at parturition based on calving date and as- chopped alfalfa hay:com silage in each diet signed randomly within block to one of the (DM basis)* were housed in a barn and four treatments (c-,c+,WE-, HPE+). cows Once for ad had completed at least one lactation but less fed a than six with an average 3054 mature equiva- libitum using feeding Inca, Northwood* lent production of greater than 8182 kg of (American Amounts offered and refused were recorded milk. me experimental periodbegan wk 5 post- daily. All cows were fed diet C after parturip m m and continued though wk 20. hjec- tion. COWSassigned to the HPE diet were to the HPE diet d-g wk tions were subcutaneous in the pocket lateral Switched to the tailhead, alternating sides daily, using 4 P s t P m m after obtain& Pretreatment milk 2.54-cm, 20-gauge needles. The C- cows were SmPleS. injected with sterile saline. Forages and concentrates were sampled Diet C was based on corn and soybean meal weekly and composited monthly. Composite (Table 1) and formulated to meet NRC (16) samples were analyzed for DM, CP, ash, Ca, recommendations for a mature cow with 636 and P (1). Acid detergent fiber and NDF were kg of BW, producing 36.4 kgJd of milk con- determined by the procedures of Robertson taking 3.5% milk fat. The HPE diet was for- and Van Soest (20). Acid detergent-insoluble mulated to supply the nutrients for cows to N was determined for corn silage and alfalfa

-

-

66F.

Journal of Dairy Science Vol. 74, No. 11, 1991

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AUSTIN ET AL.

hay (20). The acid ether extract procedure described by Drackley et al. (9) was used to remove Ca soaps from fatty acids for fat determination. Solubility and degradability of CP were determined by the Ficin protease p m e dure (19). Milk production was recorded at each milking. Two consecutive am. and p.m. milk samples were collected once weekly and composited. Composites were analyzed for fat, protein, SNF, and lactose by infr;lred spectrophotometry (Multispec, Shields Instruments Ltd, Engl.), and SCC were measured by a somatic cell counter (Foss Electric, Hillerod, DK) acCording to AOAC (1) procedures. Milk ~amples collected wk 6 to 10, 12. 14, 16, 18, and 20 postpartum were analyzed for fatty acids by GLC separation of butyl esters (6) and for N distribution by the Rowland method (21). Cows were weighed once weekly during the experiment. Two researchers independently scored body condition of cows the week of parturition and once monthly throughout the experimental period using a scale of 1 to 5

(29).

Samples of ruminal fluid were taken three times during the experimental period from all cows approximately once every 4 wk Samples were collected 2 to 4 h after feeding via an esophageal tube into bottles containing .5 ml of saturated mercuric chloride and analyzed for pH, VFA (S), and ammonia (7). Jugular blood samples were collected at the time of ruminal fluid sampling to measure serum urea N (7). At 6 to 8 wk postpartum, blood was sampled from the coccygeal artery and the subcutaneous abdominal vein to calculate arteriovenous differences across the mammary gland. Serum samples from the six highest producing cows per treatment were analyzed for AA composition by HPLC (6). Samples from all cows were not analyzed for AA to minimize number of analyses. Maximum differences were most likely to occur with the higher producing cows, although we assumed that mammary gland uptake of AA would be proportional to production for all cows. Mammary blood flow and transfer efficiency were estimated according to the procedure described by Drackley and Schingoethe (10) to identify AA possibly limiting milk production. Data were analyzed by least squares ANOVA for a split-plot design (26) using the Journal of Dairy Science Vol. 74, No. 11. 1991

TABLE 2. Sources of variation for evaluation of bST and diets. SourCe

df

Rep' bST Die? Covariate Rep x W T Rep x diet

11 1 1 1 11 11 1

WT x

diet

Error

10

Total

47

'Group (block) of four cows that calved at similar times, assigned randomly to one of four treatments;Rep = replicate. 2control or hi&

protein and energy.

general linear models procedure of SAS (SAS Inst., Inc., Cary, NC); results were expressed as least squares means. The main plot was a randomized complete block design having a 2 x 2 factorial arrangement of treatments; weeks postpartum was the subplot. Means of wk 3 and 4 were used as covariate to adjust milk production, milk composition, and DMI (27). Fisher's least significant difference test (27) was used to separate least squares means whenever significant differences were detected because of bST, diet, week postpartum,and all possible interactions. A separate ANOVA was conducted, including weeks for data to be plotted by week The sources of variation in statistical analysis are shown in Table 2. The main effect of bST was tested by the replicate by bST interaction, and diet was tested by the replicate by diet interaction when those interactions were significant (P < .05). When the interactions were not significant, main effects were tested by the overall error term (including the interaction). Significance was declared at P < .05 unless otherwise noted. RESULTS AND DISCUSSION

Chemical composition of forages and concentrates are in Table 3 and of complete diets in Table 4. Acid detergent fiber contents of diets were slightly lower than formulated values, reflecting lower ADF in corn silage than expected (16). Acid ether extract data reflected the additional dietary fat. The ficin protease procedure used is a cost effective

3923

SOMATOTROPIN AND NUTRITION

TABLE 3. Chemical composition of control (C) and high protein and energy W E ) concentrates and forages. ~~~

Concentrate Measurement

C

HPE

DM, %

89.6

91.3

Forage Corn silage Alfalfa hay 42.4

86.9

(% of DM)

8 Soluble N,l % of total N Insoluble but degradable N,l % of total N Total soluble plus degradable N,l % of total N Undegradable N,l % of total N NDF ADF ADIN, % of total N Acid ether extract Ca P Ash

20.5 34.5 48.1 82.6 17.4 13.6 3.9

23.0 25.6 58.0 83.5 16.5 12.6 4.2

3.9 .6 .7 5.9

10.5 1.1 .7 7.6

...

8.3 59.7 17.9 77.6 22.4 43.0 23.1 12.0 3.6 .3 .3 5.9

...

17.7 47.1 26.0 73.1 26.9 50.2 36.3 9.1 2.8 1.4 .3 10.0

lFicin protease procedure (19).

method for determining solubility and degrada- in situ estimates (19). Undegradable intake bility of N but does not necessarily give results protein calculated using NRC (16) estimates directly comparable with undegradable intake for various feed ingredients were 37 and 36% protein values determined by in situ proce- for C and HPE diets. dures (16). The ficin procedure sometimes (6, 10) gives lower estimates of undegradable in- Lactational Response take protein than might be expected from in Milk production was increased by bST (P < situ procedures, although some estimates by the ficin procedure have agreed very well with .07)and by the HPE diet (P< .05) (Table 5).

TABLE 4. Chemical composition of control (C) and high protein and energy

(HPE) diets.'

Diets Measurement

C

HPE

DM, %

77.1

78.0

CP Soluble N.2 % of total N Insoluble but degradable N,2 % of total N Total soluble plus degradable N.2 k of total N Undegradable N,' % of total N

16.8 43.9 35.1 79.0 21.0 30.1 16.8 3.6 .7 .5 6.9 1.65

18.0 39.5 40.0 79.5 20.5 29.6 16.9 6.9

-(% Of DM) -

NDF ADF Acid ether extract Ca P Ash m ~ Mcal/kg ?

1.o .5

7.7 1.74

lBased on analysis of forages and concentrates, as given in Table 3. *Ficin protease procedure (19). btimated.

Journal o f Dairy Science Vol. 74, No. 11, 1991

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AUSTIN ET AL.

TABLE 5. Milk production, composition, and component yields for cows fed control (C)or high protein and energy @WE) diets and treated with bST(+) or sterile saline (-).I Treatments

Main effects

bST Diet

Measurement

C-

C+

HPE-

HPE+

SE

bST

Diet

No. of cows

12 36.5

12 39.2 33.6b

12 41.4 360'

.E

.07 .03

.03

31.F

12 40.4 35.3=

.09

.27 .04

2.99 1.10

3.17 1.27

3.07 1.20

3.17 1.30

.08 .ll .02 .03

.61 .18

.OS

3.07 1.11

3.00 1.20

2.81 1.11

2.86 1.18

.04 .El .02 .06

.01 .54

.21 .65

8.50 3.10

8.52 3.43

8.22 3.23

8.28 3.42

.06 S O .07 .06

.01

.34

.67 .30

4.82 1.76

4.67 l.%

4.80 1.89

4.81 1.99

.06

.m

.38 .20

.61 .41

93.3ab

66.1ab

.69

.80

.03

m. Wd 4% FCM, kg/d Fat %

kg/d Protein %

kg/d SNF %

kg/d Lactose 96 Wd

X

P .4

.04 .53

.63

SCC

1dM

5 ~ 6 . 2 ~ 1OO.P

1.2

b . c with ~ &e ~ superscripts differ (P < .M). 'All data covariately adjusted for average of wk 3 and 4 postpartum.

h

The interaction of bST by diet was significant for 4% FCM. Although bST increased production with both diets, the incremental increase because of bST was greater with the C diet. A similar incremental response was reported by Lormore et aI. (14). Cows treated with bST had higher peak milk production (Figure 1).

304

4

1

I

I

5

6

7

,

8

, , , , , , , , , , , , 9 10 11 12 13 14 15 16 17 18 19 20 Week Postpartum

Figure 1. Milk production of cows fed control (C)or high protein and energy (HPE) diets without (-) or wich (+) bST administration.

Journal of Dairy Science Vol. 74, No. 11, 1991

Those fed the HPE diet attained peak milk production later than those fed the C diet (wk 8 vs. wk 6). After 7 wk of treatment (wk 12 postpartum), the milk production response from bST and HPE became additive. A synergistic response was reported (23) when CaLCFA were fed in 16% CP diets for 5 wk to bST-treated cows. Production was not increased by adding fat and increasing the propottion of estimated undegradable intake protein in diets already containing 18% CP, but it was increased with bST (14). The response that we obtained may have been more related to increasing protein from 16.8 to 18.0% CP than from additional fat in the HPE diet. Milk fat percentage was elevated only slightly (P = .11) by bST, which agreed with other studies (2, 11, 14, 15, 24, 26). Furthermore, fat percentage and production were not altered when HPE was fed. Previous work feeding EBB resulted in unchanged (22) or lower (6, 13) milk fat percentage, but feeding Ca-LCFA has not usually altered milk fat percentages (15, 24). Milk fatty acid composition (Table 6) was not affected by bST but was affected by diet. Shortchain fatty acids (SCFA) and medium-chain fatty acids (MCFA) were lower (P < .01) for cows con-

3925

SOMATOTROPIN AND NUTRITION

TABLE 6. Fatty acid composition of milk fat from cows fed contm-ol(C)or high protein and energy (HPE) diets without (-) or with (+) bST adminismation. Treatment Fatty acid’

C-

C+

40 6:O 8:O 100 12:o 140 141 15:O 160 16:1 17:O 18:O l8:l 18:2 18:3 200 SCFA’ MCFA’ LCFA~ Unsaturated Saturated

3.7 2.4 1.5 3.5 4.1 11.8 1.8 1.6 29.1 3.1 1.8 8.2 21.5 2.8 .3c

3.8 2.5 1.5 3.5 4.2 11.7

WE-

Main effects

HPE+

SE

Diet

30

.01 .01

.33 5.5

.04

.34

.01 .01

.67 .7 1 .77 .94 .24 .10 .49 63

.5

15.2 49.2 33.1 29.3 68.2

1.8

1.4 28.1 3.O .8 9.0 22.0 2.6 .4h .5 15.4

46.7 34.4 29.7 66.8

.Sa

.7 13.1 40.6 43.4 34.8 62.3

X

P

Q/lOO g fat) 4.2 2.3 1.4 2.5 2.8 8.9 1.2 .9 25.6 2.7 1.3 11.7 26.4 4.1

bST Diet

bST

4.1 2.3 1.2 2.4 2.7 8.7 12 .9 26.2 2.5 .7 12.4 26.8 3.9 .4& .6 12.7 40.1 44.1 34.7 62.2

.08 .05

.98 .10 .51 .13 .81 .15 9 1 .28 .63 53 .12 .48 .71 .ll .15 .47 .08 .40 .07 .73 .54 .15 26 .04 .76 .04 .17 .39 .77 .89 .I1 1.M .33 .92 .88 .92 .44

.w .w

.01

.01

.o 1 .01 .o 1 .48 .01 .01 .01 .01 .o1 .01 .o 1 .o 1 .o 1 .01

.88

92 -95 .05 .38 .39 .24 .82 .78 .49

qb%eans with unlike superscripts differ (P < .05). kxpressed as number of carbons:numker of double bonds. 2Short-chainfatty acids (s@A) = C4a to C1290; mediumchainfany acids (MCFA) = Ci43 to C i 7 : ~l;o n g - c w fatty acids (LCFA) = c183 to C200.

suming HPE,possibly a result of inhibition of de novo synthesis by long-chain fatty acids (LCFA) (17). Milk fat LCFA were increased (P e .01) for cows consuming WE, suggesting a greater incorporation of dietary fatty acids into milk fat (23). Milk fat from cows fed HPE was less saturated (P < .Ol) than for those fed the C diet. These data were close to what would be predicted from previous reports for ESB (6, 13) and Ca-LCFA (13, 24). These slight changes probably have negligible implications for dairy product manufacturing but may be attractive to those individuals desiring reduced saturated fatty acid dairy products (2). Milk protein percentage (Table 5 ) was not altered by bST treatment; however, HPE lowered milk protein percentage (P < .01). Although the bST by diet interaction was not significant (P = .21) for the entire trial, plotting data by weeks (Figure 2) indicated a possible interaction. Milk protein percentage for cows on C+ was slightly lower (P > .lo)

throughout the experimental period than for C-; milk protein percentage was generally higher for €WE+ than for HPJG (P > .05), especially after wk 15 pstpartum, and was -1 percentage unit higher (P < .05) at the end of the experimental period. This suggested that bST may have partially alleviated the protein depression caused by dietary fat, as previously proposed (5). However, the milk protein percentage from cows in the HPE+ group never was as high as from cows in the C- and C+ groups (P < .05). The experimental period may not have been long enough for adequate evaluation of the effect of bST when cows were fed added fat, because all cows were h negative or marginally adequate N balance, as estimated from NRC requirements (16) and N intake, during the first several weeks of the experiment. Such a situation would depress milk protein percentages (2). Overall treatment means of Lormore et al. (14) reflected similar trends to our data (Table 5), but they did not present their data by weeks. Journal of Dairy Science Vol. 74, No. 11, 1991

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AUSTIN ET AL.

3.35

1.25

3.25

1 .ai

3.15 1.15

*

3

3.05

E

E

0

f

2.95

0

l.1° 1.E

2.85

.

2.75

1.M)

'

.\ J

2.65 5

6

7

.95

8 9 10 11 12 13 14 15 16 17 18 19 20 Week POStDartum

4

5

6

7

8

9 1 0 1'1 12 13 14 1'5 16 17 18 19 20 Week Postpartum

Figure 2. hlilk protein percentage from cows fed control (C) or high prokin and encrgy (HPE) diets without (-) or with (+) bST administration.

Figure 3. Milk protein yield from cows fed control (C) or high protein and energy (HPE) diets without (-) or with (+) bST ad ' ' . tion.

Protein production reflected combined changes in milk production and protein percentages and generally was higher for C+ than for other treatments, but, after wk 12 postpartum,HPE+ was similar to C+ (Figure 3). Milk protein production for cows fed the HPE diet was slightly enhanced when bST was administered (P < .05, wk 13 to 20) and generally was higher for HPE+ than for C- throughout the experimental period (P < .05. wk 13 to 20). Data on various milk protein fractions (Table 7) indicated trends similar to that listed for milk protein percentages (Table 5). Lactose percentage was similar for a l l treatment groups (Table 5); therefore, changes in SNF percentage reflected changes in protein percentage. The interaction of bST with diet for SCC is probably of little biological significance, because SCC were less than 1OO,OOO/ml

for all treatments and were within expected range for early lactation multiparous cows. Dry matter intake was unaffected (P > .lo) by bST but was lower for HPE (Table 8 and Figure 4). In short-term experiments (15, 25), DMI was not affected by bST, but DMI increased in longer experiments (11, 26). Dry matter intake sometimes is reduced slightly when diets contain added fat (17). Mean BW were not affected by treatment (Table 8 and Figure 5). Any apparent differences in BW were due to inherent size of cows assigned to various treatments. Dry matter intake as a percentage of BW was not affected by bST but was lower for HPE. Body condition scores were unaffected (P > .lo) by the HPE diet, but cows receiving bST had lower (P < .01) scores during wk 15 to 20. Soderholm et al. (26) observed decreased body

TABLE 7.Milk protein fractions from cows fed control (0or high protein and energy (HPE) diets without (-) or with (+) bST administration.

Main effects

Treahnent

WE

HPE+

Measurement

C-

C+

CP NPN

3.05 .03@ 2.80 2.29 .51

2.97 2.66 2.74 .035b .OMab .W 2.75 2.45 2.53 227 2.02 2.01 .49 .43 .47

SE

bST

Diet

P

(%)

True protein CaSein Serum protein

with different superscripts differ (P c .OS).

Journal of Dairy Science Vol. 74, No. 11, 1991

bST x Diet

.06 c.01 .06

.95 .95 .87 .05 .63 .M .72

.01

.23 .01

.01 .06

.94 .01 .92 .36 .40

3927

SOMATOTROPIN AND NUTRITION

670 1

2651

C-

25.54

4

5

6

C

7

8

9

10 11 12 13 14 15 16 17 18 19 M Week Postpartum

figure 4. Dry matter intake of cows fed control (C) or diets without (-) or with high protein and energy (+) bST

administration.

5

6

7

8

9 10 11 12 13 14 15 16 17 18 19 20 Week Postpartum

Figure 5. Body weights of cows fed control (C) or high protein and magy (HPE) diets without (-) or with (+) bST administration.

condition when cows were treated with bST.

dine, isoleucine, leucine, lysine, valine, and

for the HPE diet.

tial AA also were higher for HPE. However,

Feed efficiency expressed as kilograms of milk total essential AA were higher for HPE. Veper kilogram of Dh4I was slightly higher (P > nous concentrations of arginine, histidine, iso.lo) for bST and significantly higher (P < .01) leucine, leucine, lysine, valine, and total essenSerum Amino Acids

Arterial and venous serum concentrations of

AA are given in Tables 9 and 10. respectively. No bST effects or bST by diet interactions were significant, but several dietary effects were noted. Arterial concentrations of histi-

methionine concentrations were not improved for cows fed the HPE diet, indicating a possible methionine deficiency (3). The concentration of serum AA tended to be reduced in early lactation studies in which 16% CP diets with added fat were fed (5). In the present study, the additional dietary protein with the added fat prevented such a decline in serum AA wncen-

TABLE 8. Dry matter intake, BW, efficiency of prodnction, and body condition scores of cows fed control (C)or high protein and energy OIpE) diet without (-) or with (+) bST administration.

Main effects

Treatment Measurement

c-

c+

HPE-

HPE+

SE

bST

Diet

23.7 643 3.72

24.0 638 3.77

21.9 628 3.55

222 635 3.60

.7 7

.50 .90

.06

.42

.04 .18 .01

2.53 2.47 2.61

2.61 2.51 251

257 2.59 2.72

2.61 2.32 2.50

.M .38 .M .17

1.60

1.68

1.84

1.86

.06

bST x Diet

P DMI,

Wd

B W , 43 DMI, as % B W Body condition scores, wk postp5 to 9 10 to 14 15 to 20 Feed efficiency

MilwDMI

.04 .01 .39 ~

.55

.38 .99

.El

.77

.90 .37

.06

.01

.66

.31

~~~

Journal of Dairy Science Vol. 74, No. 11, 1991

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AUSTIN ET AL.

TABLE 9. Concentration of AA in arterial m u m for cows fed control (C) or high protein and energy W E ) diets without (-) or with (+) bST *kition.

Main effects

Treatment

AA

C-

C+

HpE;-

HPE+

SE

bST

Arginine Histidine Isoleucine Leucine Lysine Methionine Phenylalanine Threonine Tryptophan Valine Total essential AA Alanine Asparagine Half-cystine Glutamic acid Glutamine Glycine Proline Serine Tyrosine Citrulline Ornithine Taurine Total nonessential AA

17.2 5.9 14.4 17.0 8.0 2.0 4.4 14.2 3.7 28.5 15.3 32.3 5.1 .lo) bST or bST by diet interaction but indicated several dietary effects. Transfer efficiencies were lower for histidine, isoleucine, leucine, lysine, and valine when cows were fed HPE compared with C, but other AA were not affected. This implied an improved status of these AA with the HPE diet. If the AA with the highest transfer efficiency is the most limiting AA for milk protein synthesis, then the first three apparent limiting AA were methionine, lysine, and phenylalanine for all treatments. Serum AA data did not indicate improvement of AA incorporation into milk protein for bST or HPE treatments. Despite increased Journal of Dairy Science Vol. 74, No. 11, 1991

.1

8.3 21.0 44.0 14.3 9.7 5.8 12.6 4.7 9.0 139.2

.05), nonsignificant variations followed the NPN content of milk (Table 7). Thomas (28) stated that blood urea freely diffuses throughout body water; thus, mi& NF" is related directly to blood urea N. CONCLUSIONS

MiLk production in early lactation was improved 11% (C+ versus C-) when cows received bST, but milk composition was not altered. Supplemental protein and energy (HPE- versus C-) improved milk production 7%. When cows receiving bST also were fed supplemental protein and energy (HF'E-b versus C-), mi& production increased 13%. Combining ESB with Ca-LCFA was an effective Journal of Dairy Science Vol. 74, No. 11, 1991

3930

AUSTJN ET AL..

TABLE 11. hexiovenow differea~cesin concentrations of AA for cows fed control (C) or high protein and energy (HPE) diets without (-) or with (+) bST administration. Treabnmt AA

C-

C+

AQw=

4.5 1.4 6.3 7.9 5.0 1.3 2.2 3.6 .4 7.8 7.9 1.6 -.l 3.3 7.7 5.0 3.2 .8 2.1

4.9 1.3 5.3 8.1 5.3 1.9 2.8 3.6 .6 6.6 4.8 13

Influence of bovine somatotropin and nutrition on production and composition of milk from dairy cows.

Forty-eight multiparous Holstein cows were used in an experiment with a 2 x 2 factorial arrangement of treatments to study interactions of bST and nut...
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