Responses of Dairy Cows Supplemented with Somatotropin During Weeks 5 Through 43 of Lactation1

PHYSIOLOGY AND MANAGEMENT Responses of Dairy Cows Supplemented with Somatotropin During Weeks 5 Through 43 of Lactation' WILLIAM CHALUPA,*** BONNIE VECCHIARELLI,* DAVID T. GALLIGAN,* J. D. FERGUSON,* L. S. BAIRD,t R. W. HEMKEN,* R. J. HARMON,t C. G. SODERHOLM,* D. E. OTTERBY,* R. J. ANNEXSTAD,* J. G. LINN,* W. P. HANSEN,* F. R. EHLE,* D. L. PALMQUIST,§ and R. G. EGGERT" 'Center for Animal Health and Productivity, School of Veterinary Medicine, University of Pennsylvania, Kennett Square 19348 TDepartment of Animal Sciences, University of Kentucky, Lexington 40.546 tDepartment of Animal Science, University of Minnesota, St Paul 55108 §Department of Dairy Science, Ohio Agricultural Research and Development Center, The Ohio State University, Wooster 4461091 liAmerican Cyanamid C O , Princeton, NJ 08540

ABSTRACT

Beginning a t wk 5 of lactation, 136 cows ( 3 4 per treatment) were supplemented daily for 38 wk with 0, 10.3, 20.6, or 41.2 mg of recombinantly derived bST monomer. Cows were obtained from University of Kentucky, University of Minnesota, University of Pennsylvania, and The Ohio State University. Nine cows ( 4 at 0 mgld, 1 a t 10.3 mgld, 1 a t 20.6 mg/d, and 3 a t 41.2 mg/d) did not complete the experiment because of health problems. Data from these cows were included in the reproduction and health databases but not in the production database. Cows supplemented with bST produced more milk, consumed more feed, had lower rates of BW gain, and had improved efficiencies of milk production (conversion of feed and NEL to milk). Additional increases in productivity were modest a t 20.6 and 41.2 mg/d versus productivity a t 10.3 mgld of bST. Concentrations of fat, protein, and TS in milk were unaffected. At 10.3 mg/d, bST did not adversely affect reproduction or health. ( Key words: somatotropin, lactation, health) INTRODUCTION

Bovine somatotropin is a management tool that can improve the efficiency of milk production and economic returns from dairy farming by partitioning nutrients to milk synthesis ( 6 , 7, 9, 13, 16, 18, 38). This paper summarizes results presented previously in abstract form ( 4 , 12, 17, 37, 46). The primary objective was to determine production

Received J u n e 6, 1995. Accepted December 27, 1995. 'Supported by University funds and by American Cyanamid Co. 2Corresponding author. 1996 J Dairy Sci 79:8W12

responses to three different doses of bST administered throughout the entire lactation cycle. The effects of bST on reproduction and cow health were also recorded. MATERIALS AND METHODS cows

One hundred thirty-six cows a t University of Kentucky, University of Minnesota, University of Pennsylvania, and The Ohio State University were used. Cows were assigned to 34 replications of 4 cows on the basis of breed, parity (primiparous or multiparous), and calving date. The experiment utilized 32 primiparous Holsteins, 84 multiparous Holsteins, 4 primiparous Jerseys, 8 multiparous Jerseys, 4 multiparous Brown Swiss, and 4 multiparous Ayrshires (Table 1). Of the 136 cows (Table 1). 9 did not complete the 38-wk experiment because of health problems (Table 2 ) . There was no indication that supplemental bST was responsible for these health problems. These 9 cows were included in the health and reproduction databases but were removed from the production database. Treatments

Beginning a t d 28 to 35 of lactation, cows were supplemented daily with 0, 10.3, 20.6, or 41.2 mg/d of recombinantly derived bST monomer. To simplify management, cows started treatments on the same day of the week (i.e., Wednesday). Recombinant bST, purified to greater than 95% homogeneity, was supplied by American Cyanamid Co. (Princeton, N J ) in lyophilized form in 100-ml serum bottles. The dry preparation was reconstituted with physiological saline a t pH 9.4 to provide doses of

800

801

RESPONSES TO SOMATOTROPIN

TABLE 1. Breed and parity of cows used to evaluate responses to bST. Breed and parity

University of Kentucky

University of Minnesota

The Ohio State University

University of Pennsylvania

Total

(no. of cows) Holstein Primiparous Multiparous Jersey Primiparous Multiparous Brown Swiss Multiparous Ayrshire Multiparous Total

8 28

8 12

8 24

32 84

0 4

0 0

4 4

0 0

4 8

0

0

4

0

4

0 32

0 36

4 36

0 32

4 136

8 20

10.3,20.6,and 41.2 mg/d when cows were injected subcutaneously with 1.25,2.5,or 5 ml of the reconstituted bST solution. Control cows ( 0 mg/d of bST) were injected daily with 2.5 (Kentucky) or 5 (Ohio, Minnesota, and Pennsylvania) ml of physiological saline. Injections were administered with 18- or 20-gauge needles in one of four alternating sites on the neck and shoulder (right dorsal, right ventral, left dorsal, and left ventral). Management Cows a t Kentucky, Minnesota, and Ohio were housed in tie-stall barns; those a t Pennsylvania were housed in a free-stall barn. Cows were milked twice daily in milking parlors a t Kentucky and Pennsylvania and in tie stalls a t Minnesota and Ohio. Milk weights were recorded a t each milking, and weekly means were computed. Weekly a.m. and p.m. milk

samples were obtained for analysis of milk composition. Fat and protein (infrared assay) and somatic cells (Coulter counter; Coulter Electronics, Hialeah, FL) were determined at state DHIA laboratories for cows at Kentucky, Ohio, and Pennsylvania. At Minnesota, fat was assayed by the Babcock method, and protein was determined by Kjeldahl N x 6.25.Total solids were measured by drying a t 60°C t o a constant weight. Fat-corrected (3.5%)milk was calculated by the following equation: FCM = (0.4324x kilograms of milk) + (16.218x kilograms of fat). Rations with 15 to 17% CP and 1.47t o 1.85 Mcal/ kg of NEL (Table 3 ) were fed for ad libitum intake. So t h a t responses to bST could be evaluated independently of dietary changes, nutrient densities of diets were not lowered as production declined. In addition, cows at Kentucky received 1.36 kg/d of alfalfa hay; those a t Ohio were supplemented with 0.33 kg of soybean meal or protein concentrate per kilogram of milk above 40 kg/d.

TABLE 2. Cows that did not complete the experiment because of health problems.' Location

Identification number Treatment

0 0 10.3 20.6 41.2

University of Kentucky University of Minnesota The Ohio State University The Ohio State University University of Pennsylvania University of Minnesota The Ohio State University

778 1111 1073 232 262 1164 96

238 210 112 126 168 175 126

41.2 41.2

The Ohio State University Universitv of Pennsvlvania

571 160

238 112

bST (mg/d) 0 0

Reason-

(d) Leukemia Mastitis Hardware Hardware Johne's Mastitis Mastitis Obstruction of the small intestine Leukemia

'Removed from the production database but not from the health or reproduction databases.

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CHALUPA ET AL

Feed intake was measured daily, and weekly means were computed. Monthly composites of diets were analyzed for DM, CP, ADF, Ca, and P. The NEL of diets was calculated using methods described subsequently. Cows were weighed prior to treatment and a t weekly intervals during the treatment period. Changes in BW of each cow were estimated by regression analysis of BW on week of treatment.

the period of bST treatment, health problems and treatments were recorded. When cows were nearing the completion of the experiment, they were evaluated for physical soundness by an independent dairy consultant (Roger Meads, Hortonville, WI). The consultant was not aware of treatments.

Reproduction and Cow Health

Production d a t a . Milk composition, milk production, and feed intake during the 2 wk prior to treatment were used as covariables. Least squares means are presented. To evaluate responses over the entire experiment, mean values for each cow were computed for concentrations of fat, protein, TS, and somatic cells in milk; daily production of milk and FCM; feed intake; and feed efficiency. Because SCC did not follow a normal

Cows were observed for estrus a t least twice daily, and breeding by AI began a t 60 t o 70 d postpartum. Cows were given physical examinations prior t o treatment initiation and a t the end of the 38-wk treatment period. Cows with health problems or unexpectedly low production during the first 4 wk of lactation (prior t o treatment) were replaced. During

Statistics

TABLE 3. Composition and analysis of total mixed diets

Composition

University of Kentucky1

University of Minnesota

The Ohio State University2

University of Pennsylvania

( % of DM)

Ingredient Corn silage Alfalfa hay Alfalfa haylage Ground shelled corn Ground oats Hominy meal Wheat midds Soybean meal Distillers grains Beet pulp Molasses Tallow Unifat (M-3713 Urea Minerals and vitamins4 Ame ribond5 Analysis CP NEL, McaYkg ADF Ca P

41.7

... 18.0 24.3 10.1 . . .

28.0 22.0

. . . 27.8 5.3

30.0

10.5 . . .

10.5 12.5 2.4 . . .

. . .

1.4 . . .

2.5 1.0

. . .

. . .

3.1 1.4 15.0 1.476 18.6 0.94 0.73

20.8 20.0

0.5 2.4

16.5 1.6a6 19.6 1.21 0.54

1.8 0.2 2.6

17.1 1.857 21.1 0.99 0.38

25 7 . . . 16.6 30.1

11.5 11.5

. . . . . . 4.7

16.4 1.72@ 21.3 0.86 0.61

'Cows also received 1.36 kg/d of alfalfa hay; analysis included nutrients from alfalfa hay. Wows also received 0.33 kg of soybean meal or protein supplement per kilogram of milk above 40 kg/d; analysis did not include nutrients from additional protein. 3Jacob Stern and Sons, Inc. (Jenkentown, PA). *Mineral and vitamin supplements were included to meet or exceed NRC ( 3 6 1 recommendations. 5Lignosulfate pellet binder (Southern States Cooperative, Richmond, VA). 'Xalculated from values for feed ingredients recommended by the NRC ( 3 6 j . (megacalories per kilogram) = 2.35 - (0.024 x percentage of ADF). ~ N E L(megacalories per kilogram) = 2.136 - (0.02 x percentage of ADF); based on regression of ADF on NEL of feed ingredients recommended by the NRC ( 3 6 ) . Journal of Dairy Science Vol. 79, No. 5, 1996

RESPONSES TO SOMATOTROPIN

803

distribution, they were converted to DHIA somatic variation, but the interaction of university and bST cell scores. These data were analyzed as a randomized was not significant ( P > 0.34). As described previcomplete block experiment using the general linear ously, cows with health problems (Table 2 ) were models procedure of SAS ( 4 4 ) ; university, treatment, removed from the production database. During the and the interaction of university and treatment were time of supplementation with 0, 10.3, 20.6, and 41.2 mg/d of bST, mean production of these cows was 27.2, sources of variation. Responses a t various stages of the lactation cycle 25.6, 39.9, and 35.5 kg/d of FCM. Cows a t Minnesota and Pennsylvania had the larwere evaluated by calculating the means of FCM, feed gest increases in production of milk and FCM; those intake, efficiency, and BW for each cow by 4-wk periat Ohio had the smallest increase (Tables 5 and 6 ) . ods. Data were analyzed as a repeated measures exAlthough different in magnitude (Table 7 ) , FCM periment using the general linear models procedure of production increased for primiparous ( P = 0.07 ) and SAS ( 4 4 1; university, treatment, period, replicate multiparous ( P < 0.01) Holsteins and for the com(treatment), the interaction of university and treatbined parities of other breeds ( P = 0.13). ment, and the interaction of treatment and period Milk composition. Concentrations of fat, protein, were sources of variation. and TS in milk (Table 4 ) were unaffected by supExamining effects of breed and parity on responses plemental bST. Milk composition differed among t o bST presented a problem because all breeds were universities ( P < 0.01), but the interaction of univernot represented a t all universities and because repli- sity and bST was not significant ( P > 0.50). Milk fat cations of multiparous Holsteins were not formed on test was selected as a n example of the effect of bST on the basis of parity. For statistical analyses, we milk composition of cows at the four universities (Tagrouped Holsteins according to parity (primiparous ble 8). Fat test was highest for cows at Kentucky, but vs. multiparous). Jerseys, Brown Swiss, and Ayr- bST did not have a significant ( P > 0.14) impact on shires were grouped together, regardless of parity. concentration of milk fat a t any of the locations. Feed intake. Cows supplemented with bST conOur randomized complete block design analysis with the general linear models procedure of SAS ( 4 4 1 only sumed more ( P = 0.03) feed than did control cows considered treatment as a source of variation. Least (Table 4 ) . University was a significant source of squares means were not adjusted to reflect production variation ( P = 0.03))but the interaction of university during the 2 wk prior to treatment, because such an and bST was not significant ( P = 0.33). When FCM adjustment would have masked differences in produc- was used as a covariable, intakes were 21.4, 20.9, 21.0, and 21.4 kg/d for cows receiving 0, 10.3, 20.3, tion based on breed and parity. Reproduction and cow health. Data were anal- and 41.2 mg/d of bST, respectively, indicating that yzed using the CATMOD and FREQ procedures of cows consumed additional feed in response to inSAS ( 4 4 ) . Sources of variation and treatment com- creased milk production. Emciency. Even though cows consumed more parisons are detailed in the footnotes of Tables 9, 10, feed, the three estimates of production efficiency and 12. showed that cows supplemented with bST produced more ( P < 0.01) FCM per kilogram of feed and per RESULTS megacalorie of NEL consumed (Table 4 ) . Although cows a t the four universities had different efficiencies Production ( P < 0.01), the interaction of bST and university was not significant ( P > 0.34). Overall responses of milk production, milk compoBW change. Control and treated cows gained BW sition, feed intake, efficiency, and BW changes to during the 266-d experiment, but, as bST increased, supplemental bST are summarized in Table 4. rate of BW gain decreased ( P < 0.01; Table 4). Responses of milk production, 3.5% FCM production, Neither university nor the interaction of bST and and concentration of fat in milk to supplemental bST university was a significant source of variation ( P > for cows at the four universities are presented in 0.13). Tables 5, 6, and 8. Effects of breed and parity on Stage of lactation. Fat-corrected milk, feed inresponses of milk and FCM to supplemental bST are take, feed efficiency, and BW by 4-wk periods are presented in Table 7. Responses of DMI, 3.5% FCM, presented in Figure 1.The FCM production increased feed efficiency (FCM/DMI), and BW are shown in ( P < 0.05) with all dosages of bST during wk 4 to 36 Figure 1. of treatment. During the final 4 wk of lactation, supMilk production. Overall, production of milk and plementation with 10.3 and 41.2 mgld of bST, but not FCM was increased ( P < 0.01) by supplemental bST with 20.6 of mg/d of bST, promoted increases ( P < (Table 4). University was a significant source of 0.05) in 3.5% FCM production. Increases in feed inJournal of Dairy Science Vol. 79, No. 5, 1996

804

CHALUPA ET AL.

take were not significant ( P> 0.05) for the first 8 wk of treatment but thereafter were dose-dependent. Beginning with the 1st wk of treatment, cows produced more ( P< 0.05) FCM per kilogram of feed consumed; no differences in response caused by the amount of bST administered were apparent. After 32 wk of lactation, efficiency of cows supplemented with 20.6 mg/ d of bST was not statistically significant ( P> 0.05). During the first 20 wk of supplementation, increases in BW were similar for all doses of bST. Thereafter, control cows had the greatest BW increase, and cows

supplemented with 41.2mg/d of bST had the smallest increases. Reproduction and Cow Health

Supplementation with 41.2 mg/d of bST reduced pregnancy rate ( P< 0.05) but did not affect AI services or conception rate ( P= 0.22)or days open ( P = 0.56) of pregnant cows (Table 9 ) . At Ohio State, only 50% of the cows became pregnant; those cows required more AI and were open longer than were cows at the other universities.

TABLE 4. Milk composition, milk production, feed intake, efficiency, and BW change of cows supplemented daily with bST during wk 5 to 43 of lactation. Contrast

bST Measurement

0 mg/d

10.3 mg/d

20.6 mg/d

41.2 m d d

bST

U

bST x U

P' Cows, no. Milk composition, % Fat X SE PIotein

X SE

30

33

33

31

SE

. . .

. .

3.68 0.09

3.88 0.08

3.82 0.08

3.83 0.09

0.43

<0.01

0.95

3.19 0.03

3.21 0.03

3.21 0.03

3.18 0.03

0.84

co.01

0.50

12.74 0.13

12.86 0.12

12.83 0.12

13.00 0.12

0.52

<0.01

0.86

27.78 0.6

29.5b 0.6

30.4bc 0.6

32.2c 0.7

<0.01

<0.01

0.41

27.7a 0.6

31.0b 0.6

31.8b 0.6

33.1c 0.6

<0.01

0.17

0.34

20.28 0.4

20.88 0.4

21.3ab 0.4

21.gb 0.4

0.03

<0.01

0.33

TS

X

. . .

Production, kg/d Milk

X

SE 3,5% FCM

X SE D-MI , kg/d X

SE Effciency Alparent2

X SE

1.348 0.03

1.48b 0.03

1.51b 0.03

1.51b 0.03

<0.01

<0.01

0.57

0.80a 0.02

0.88b 0.02

0.9Ob 0.02

0.9Ob 0.02

<0.01

<0.01

0.61

0.858 0.02

0.92b 0.02

0.93b 0.02

0.93b 0.02

<0.01

<0.01

0.34

0.37a 0.03

0.29ab 0.03

0.24h 0.03

0.20c 0.03

<0.01

0.13

0.67

Gross O_bserved3

X SE Corrected4

X

SE B Y Change, kgld

X

SE

a.b.cLeast squares means within a column followed by different superscript letters differ ( P < 0.05). 'Probability that bST, university ( U ) , and the interaction of bST and U (bST x U ) affected production. 2Apparent efficiency = (kilograms of 3.56 FCM)/(kilograms of feed intake). 30bserved gross efficiency = (kilograms of 3.5% FCM)/(megacalories of NEL intake). 4Corrected gross efficiency = (kilograms of 3.5% FCM)/(megacalories of NEL intake minus megacalories of energy in BW change) where BW gain contains 5.12 McaVkg and BW loss provides 4.92 McaYkg ( 3 3 ) . Journal of Dairy Science Vol. 79, No. 5. 1996

805

RESPONSES TO SOMATOTROPIN

TABLE 5. Milk production in response to daily supplementation with bST during wk 5 to 43 of lactation. Response to bST

Daily production

Location

10.3 mg/d

(kg/d) University of Kentucky University of Minnesota The Ohio State University University of Pennsylvania

All

20.6 mg/d

41.2 mg/d

P1

4.38 5.38 4.78 5.38 4.58

0.07 <0.01

(kg/d)2

24.8 28.8 30.9 24.0 27.7

2.8 2.58 -1.5 4.98 1.88

1.5 5.88

0.5 4.78 2.88

<0.01

0.02 co.01

BResponse relative to 0 mg/d ( P < 0.05). 'Probability that bST affected milk production 2Response to bST relative to 0 mg/d of bST.

The number of cows with specific health problems is summarized in Table 10. The CATMOD procedure of SAS (44)showed that bST ( P e 0.01)and university ( P = 0.04),but not the interaction of bST and university ( P= 0.19),affected fertility. Fisher's twotailed exact test ( 44) demonstrated that supplementation with 41.2 mg/d of bST reduced ( P c 0.01) pregnancy rate. The common relative risk (44) showed that infertility was about three times greater for cows treated with 41.2 mg/d of bST than for untreated cows. Somatotropin did not affect ( P > 0.20) the incidence of ketosis, abomasal displacement, feet and leg problems, or clinical mastitis. However, Fisher's two-tailed exact test (44)and the relative risk procedure ( 44 showed that the number of cows with feet and leg problems ( P = 0.08) and those requiring antibiotic therapy for mastitis ( P = 0.10) tended to be higher when cows were supplemented with 41.2 mg/d of bST. The somatic cell scores acquired from the DHIA were highest at Kentucky and Pennsylvania and lowest at Minnesota and Ohio (Table 11). Within

universities, bST did not affect somatic cell scores, but, overall, somatic cell scores were higher ( P = 0.05) for cows receiving 41.2mg/d of bST (Table 11). The summary evaluation of cows by the independent consultant near the end of the experiment is presented in Table 12. Control cows and cows supplemented with 10.3 and 20.6 mg/d of bST had body condition scores of 3;body condition score was 3 minus for cows supplemented with 41.2 mg/d of bST. Supplementation with bST did not significantly affect the number of cows with abnormal feet and legs, gait, and udders. DISCUSSION

Production

Milk production. Cows at all locations produced more milk and FCM when supplemented with bST. Although the interaction of bST and university was not a significant source of variation, the magnitude of responses varied among the four universities. Higher

TABLE 6. Production of 3.5% FCM in response to daily supplementation with bST during wk 5 to 43 of lactation. Response to bST

Daily production

Location ~

~~

10.3 mg/d

20.6 mg/d

3.48 2.8 1.7 6.88 3.38

2.3 6.88 2.4 5.98 4.la

(kg) University of Kentucky University of Minnesota The Ohio State University University of Pennsylvania All

27.0 29.1 28.9 24.2 27.7

41.2 mR/d

Pl

4.0a 6.48 5.98 6.98 5.48

0.09 <0.01 0.05 <0.01

~~

(kg/dF

<0.01

aResponse relative to 0 mg/d ( P < 0.05). 'Probability that bST affected 3.5% FCM. 2Response to bST relative to 0 mg/d of bST. Journal of Dairy Science Vol. 79, No. 5, 1996

806

CHALUPA ET AL.

doses of bST were needed to achieve production responses for primiparous Holsteins than for multiparous Holsteins. Although cow numbers were small, breeds other than Holsteins responded similarly. Effects of bST on milk production have been reviewed by others (13, 18, 34, 39). In the summary prepared by Chilliard ( 18>, daily supplementation with 10 t o 50 mg/d of bST increased milk production by 4.1 to 6.2 kgld. Administration of 320 to 960 mg of bST a t 28-d intervals in a sustained-release vehicle increased milk production by 1.5 to 3.4 kg/d. Milk

42 n

~

I

38

? * 34 5

E

production increased 4.7 kg/d when 500 mg of bST were administered a t 14-d intervals in a sustainedrelease preparation. Similar responses were obtained under commercial conditions ( 2 , 3, 14, 15, 21, 23, 24, 48) in experiments in which bST was administered for 2 or 3 consecutive yr (1, 25, 26, 27, 39, 4 2 ) and when cows were milked three ( 2 9 ) or four ( 3 ) times daily. Effects of parity on responses to bST were not resolved completely. Data from some experiments (28, 4 8 ) suggested that higher doses of supplemental bST were needed to achieve production responses by

zn

a

30

U.

0

26

LL

c3

22

I 0 26

$

3 z

4

i

1

i

8 12 16 20 24 28 32 36 WEEK OF TREATMENT

I T

0 4 8 12 16 20 24 28 32 36 WEEK OF TREATMENT

650 I

I

22 20

0 W

E

18 16

0

4

8 12 16 20 24 28 32 36 WEEK OF TREATMENT

52SY 0

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Figure 1. Fat-corrected milk (3.5%), feed intake, feed efficiency, and BW of cows supplemented daily with 0 mg/d (.I, 20.6 mg/d (a), or 41.2 mg/d ( 01 of bST during wk 5 to 43 of lactation. Journal of Dairy Science Vol. 79, No. 5, 1996

1

10.3 mg/d (01,

807

RESPONSES TO SOMATOTROPIN

primiparous cows, but other research (8, 12, 2 3 ) showed that primiparous cows responded identically to multiparous cows. Most research has been with Holsteins, but milk production responses have been reported for all dairy breeds examined, including North American and European breeds ( 61, Murrah buffalo (61, South American breeds (331, and African breeds ( 3 2 ) . Milk composition. Concentrations of fat, protein, and TS in milk were not affected by supplemental bST a t any of the locations, which reflects the high nutrient densities of the diets, because effects of supplemental bST on milk composition seemed to be related t o nutritional status. Somatotropin did not change milk composition when cows were fed diets to provide positive balances of energy and protein ( 5 , 6, 16, 34, 3 8 ) . When cows are in negative energy balance, fatty acids are mobilized from adipose tissue, and milk fat test increases. When cows are in negative protein balance, the concentration of protein in milk decreases. In general, effects of dietary energy and protein on concentrations of fat and protein in milk from cows supplemented with bST are similar to alterations when high producing cows are fed diets that do not provide adequate energy or protein. Feed intake. When bST is administered to cows, more nutrients are needed for increased synthesis of milk protein, fat, and lactose. Initially, body stores of protein, fatty acids, and glycogen may provide additional nutrients, but nutrients for prolonged increases of production are derived from coordinated changes in the metabolism of many tissues and by increased feed intake ( 6 , 16, 34, 3 8 ) . Our cows began to increase feed intake after 4 wk of bST supplementation. Covariable adjustment for

the increased production of FCM showed that most of the increased feed consumption was accounted for by higher milk production. Thus, cows supplemented with bST increased feed intake in response to increased production in a predictable manner. Therefore, current equations ( 3 6 ) used to estimate feed intake can be applied to cows that are supplemented with bST. Eficiency. Most attention has been directed toward increases in milk production, but economic benefits are derived from improvements in feed e f i ciency (FCM/DMI, FCM/NEL intake, and FCM/NEL intake corrected for BUT gain or loss). In our study, the three methods of expressing efficiency showed improvements with bST supplementation. Even though feed consumption increased, more dietary nutrients were captured in milk (6, 16, 34, 3 8 ) . Somatotropin has little effect on rumen fermentation, flow of nutrients to the small intestine, and total tract digestibility ( 2 0 , 30, 31, 40, 43, 45, 49, 5 1 ) . I n studies conducted with nutritional status ranging from negative to positive balances of energy and protein, neither maintenance requirements ( 3 0 , 45, 4 9 ) nor the partial efficiency of milk synthesis ( 3 0 , 45, 4 9 ) was altered when lactating cows were supplemented with bST. The amount of energy lost as heat appeared to depend on energy balance ( 4 5 , 4 9 ) . When cows were in negative energy balance, supplementation with bST increased heat energy loss. The increased heat energy loss, however, was that which would be predicted for cows producing more milk. When energy balance was not negative, supplementation with bST did not affect energy lost as heat.

TABLE 7. Effect of breed and parity on production of 3.5% FCM by cows supplemented with bST during wk 5 to 43 of lactation.

Breed

Lactation

Holstein

1

Holstein

>1

Other4

~115

Response to bST

Daily production

10.3 mg/d

(kg) 26.6 ( n = 8)s 28.1 ( n = 18) 24.5 ( n = 4)

0.5 (n = 7 ) 5.3a ( n = 21) 4.8 ( n = 5)

20.6 mg/d

(kg/d)2 2.9 ( n = 8) 6.6a ( n = 20) 3.4 ( n = 5)

41.2 mg/d 4.9a ( n = 8) 6.4a ( n = 18) 5.8a ( n = 5)

PI 0.07 <0.01 0.13

aResponse relative t o 0 mg/d ( P < 0.05). 'Probability that bST affected milk production. 2Response to bST relative to 0 mg/d of bST. 3Number of cows. *Jersey, Brown Swiss, and Ayrshire. SPrimiparous and multiparous cows. Journal of Dairy Science Vol. 79, No. 5, 1996

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CHALUPA ET AL.

TABLE 8. Fat percentage of milk from cows supplemented daily with bST during wk 5 to 43 of lactation. bST Location

0 mgld

10.3 mg/d

20.6 mgld

41.2 mg/d

P1

University of Kentucky University of Minnesota The Ohio State University University of Pennsylvania All

4.14 3.69 3.39 3.64 3.68

4.14 3.66 3.78 4.00 3.88

4.17 3.73 3.58 3.70 3.82

4.01 3.80 3.59 3.97 3.83

0.81 0.71 0.69 0.14 0.43

'Probability that bST affected milk fat percentage.

Because bST did not affect either digestion of feeds or the efficiency of utilizing absorbed nutrients for milk synthesis, there must be other reasons for the improved feed efficiency. When cows produce more milk, they usually consume more feed. The absolute requirements for maintenance is not changed, but the relative proportion of intake nutrients needed for maintenance is less, and the proportion available for milk synthesis is greater. Thus, the relative main-

tenance requirement is diluted as milk production increases. In addition, bST partitions calories to milk production a t the expense of body fat t 3 5 ) . Thus, bST increases the capture of dietary nutrients in milk by decreasing the relative proportion of consumed nutrients needed for maintenance and by partitioning nutrients into milk rather than into body reserves. BW change. All treatment groups gained BW during the experiment, but, as bST increased, rate of

TABLE 9. Reproduction of cows supplemented daily with bST during wk 5 to 43 of lactation. bST Location

0 mgld

10.3 mg/d

University of Kentucky University of Minnesota The Ohio State University University of Pennsylvania Total

618 819 719 718 28/34

Pregnant cowdtotal cows (no.lno.) 618 418 518 919 819 4l9a 419 3/98 4l9 718 618 L/8a 26/34 21/34 14l34a

University of Kentucky University of Minnesota The Ohio State University University of Pennsylvania Mean University of Kentucky University of Minnesota The Ohio State University University of Pennsylvania Mean University of Kentucky University of Minnesota The Ohio State University University of Pennsylvania Mean

72 63 48 63 61 3.0 1.4 3.3 1.6 2.3 148 82 178 107 126

20.6 mg/d

4 1 mgld

First estrus2 ( d ) 93 59 79 55 67 66 61 70 63 67 71 122 69 69 78 Services per pregnancy3 ( n o .) 1.58 2.0 1.2a 1.3 1.9 1.8 2.0 4.78 2.5 1.7 1.7 1.0 1.6 2.3 1.7 Open3 ( d ) 100 157 103 110 83 116 130 217 185 112 115 141 111 128 133

Total or mean

Contrast bST

U . .

. . .

0.72 0.04 0.21 <0.01 <0.01

76 63 61 80 . . .

0.26 0.71 0.42 0.21 0.19

2 1/32xy 29/36x 18/36y 2 1/32xy

2.0x 1.5x 3.0y 1.6x

. . . 125x 96x 175Y 113x

. . .

0.10 0.65 0.11 0.85 0.22

0.13 0.27 0.41 0.85 0.56

bST x U

P' . .. . . . . .. . . . . . . . . . .. . ,

0.04

0.20

. . . .. . . . . ... . . . . . . . . . .. . 0.28

. . . . . . .

.

0.20

. . . . . . . . . . . . . . . .

0.02

0.19

. .. . . . . .. , . . . . . . . . . .. . . . 0.01 0.15

aResponse relative to 0 mgld of bST ( P < 0.05). XWverall response at universities differed ( P < 0.05). 'Using the CATMOD procedure of SAS ( 4 4 ) , probability that bST, university ( U ) , and the interaction of bST and U (bST x U ) affected reproduction. *All cows. 3Pregnant cows. Journal of Dairy Science Vol. 79, No. 5, 1996

809

RESPONSES TO SOMATOTROPIN

gain decreased. Change in BW, however, did not adequately reflect the use of body reserves to provide nutrients for milk synthesis, nor did it reflect the repletion of body reserves. Supplementation of cows with bST caused changes in body composition (10, 19, 35, 46). The main effect was decreased body fat, reflecting the partitioning of calories by bST to milk a t the expense of fat deposition. Reproduction and Cow Health

Although evaluation of supplemental bST on reproduction and cow health was not the primary

objective of our experiment, observations were recorded. Several statistical methods were used. Initially, data were analyzed using the CATMOD procedure of SAS (441 t o determine effects of bST, university, and the interaction of bST and university. To examine effects of bST further, the FREQ procedure of SAS (441 was employed to compare 0 versus 10.3, 20.6,or 41.2 mg/d of bST using Fisher’s two-tailed exact test and common relative risk (MantelHaensel). Supplementation with 41.2 mg/d of bST during the breeding period decreased the number of cows that became pregnant. However, when only pregnant cows were considered, AI services, conception rate, and

TABLE 10. Specific health problems of cows supplemented daily with bST during wk 5 to 43 of lactation. bST

Contrast

Problem

0 mg/d

10.3 mg/d

20.6 mgld

41.2 mgld

Total cows, no. Not pregnant, no.

34 6

34 8 0.77 1.33 0.52 3.43 3 0.61 3.00 0.38 23.46 3 0.61 3.00 0.36 2.50 4 1.00 1.00

34 13 0.10 2.17 0.97 4.86

34 20 <0.01 3.33 1.67 6.58

P* Relative risk3 Lower limit4 Upper limit4 Ketosis,s no.

P Relative risk Lower limit Upper limit DA,6 no.

P Relative risk Lower limit Upper limit Feet and legs,7 no.

P Relative risk Lower limit Upper limit Mastitis: no.

. . . 1.00

. . . . . .

1 . . . 1.00 . . . . . . 1

. . . 1.00

. . .

. . . 4 . . . 1.00

. . . . . . 7

P

. . .

Relative risk Lower limit Upper limit

, . .

1.00 . . .

. . .

. . . 12 0.17 2.00 0.87 4.58

1

1

1.00 1.00

1.00 1.00

bST

U

bST x U

. . . . . . . . . ~ 0 . 0 1 0.04

. . . . . . . . . . . . . . . . 0.86 .

.

.

. .

0.46

. . .

. . . . .

. . .

. . . . .

2 1.00 2.00 0.57 1.34 5 1.00 1.25 0.36 4.30 10 0.39 1.66 0.75 3.71

4

13 0.10 2.16 1.02 4.62

0.69 ,

. . . . . .

0.12

. . . .

0.97

. . . . . . . . . . .

. . . . . .

0.36 4.00 0.61 2.61 11 0.08 2.75 1.04 7.34

0.19

.

.

.

. ,

0.97 . . .

0.20

0.24

0.87

021

<001

035

. . . . . . . . .

. . . . . . . . . . . . . . . . . .

‘Using the CATMOD procedure of SAS ( 4 4 ) , the probability that bST, university ( U ) , and the interaction of bST and U (bST x U ) affected cow health. Wsing Fisher’s two-tailed exact test in the FREQ procedure of SAS (441, the probability that health of cows supplemented with 10.3, 20.6, or 41.2 mg/d of bST was different from that of cows supplemented with 0 mg/d of bST. 3Common relative risk (Mantel-Haensel) calculated using the FREQ procedure of SAS ( 4 4 ) to compare 0 versus 10.3, 20.6, or 41.2 mg/d of bST. 4Limits calculated using 0.95 confidence intervals. 5Ketones in urine. GLeft displacement of abomasum requiring surgery 71ncludes foot rot, abscesses and seromas on feet and hips, and lameness but not routine trimming of feet BRequired antibiotic treatment. Category does not include cows with teat injuries that developed mastitis ( 2 cows a t the University of Minnesota that received 20.6 mg/d of bST). Journal of Dairy Science Vol. 79,

No. 5, 1996

810

CHALUPA ET AL

TABLE 11. Somatic cell scores of cows supplemented daily with bST during wk 5 to 43 of lactation. Scores were acquired from the DHIA. Contrast

bST Location

0 meld

10.3 m d d

20.6 m d d

41.2 meld

Mean

bST

University of Kentucky University of Minnesota The Ohio State University University of Pennsylvania All

3.7 2.1 2.4 3.6 3.1

3.8 2.1 3.2 4.3 3.3

3.6 2.2 3.8 4.0 3.4

4.8 3.3 3.0 4.6 3.9a

4.0X 2.5y 3.2y 4.1X

0.19 0 18 0.13 0 58 0.05

U

bST x U

P'

. . .

<0.01

0.41

aResponse relative to 0 mg/d of bST ( P < 0.05). XlYOverall response at universities differed iP < 0.05) 'Probability that bST, university ( U ) , and interaction of bST and U ibST x U1 affected somatic cell scores.

days open were not affected. None of the statistical methods used showed negative impacts of 10.3 or 20.6 mgld of bST on reproduction. Ketosis, abomasal displacement, feet and leg disorders, and mastitis were specific health problems recorded. Fisher's two-tailed exact test ( 4 4 ) and the

Mantel-Haensel relative risk ( 4 4 ) indicated that cows supplemented with 41.2 mg/d of bST tended t o have more feet and leg problems and that more cows required antibiotic treatment for mastitis. At 10.3 and 20.6 mg/d of bST, there was no statistical indication ( P > 0.10) of increases in pregnancy failure,

TABLE 12. Evaluation of cows by a n independent consultant after supplementation with bST for 36 wk.1 bST

Contrast

Measurement

0 mg/d

10.3 mg/d

20.6 mg/d

41.2 mg/d

bST

Total cows, no. Body condition3 Feet and legs,4 no.

32 3

33

33 38 0.54 1.18 0.49 2.83 2 1.00 0.92 0.15 5.52 7 0.30 1.63 0.45 5.92

30 3 11 0 08 1.58 0 71 3.55 5 0.25 1.82 0.47 7.08 2 1.00 0.78 0.17 3.64

. . . . . .

U

bST x U P2

P5 Relative risk6 Lower limit7 Upper limit7 Abnormal gait,a no. P Relative risk Lower limit Upper limit Abnormal udder,g no. P Relative risk Lower limit Upper limit

5 . . . 1.00 . . . . . .

2 . . .

1.00 . . . . . .

3

. . . 1.00 . . .

. . .

3 5 1.00 0.97 0.39 2.42 5 0.43 1.57 0.35 7.14

7 0.30 1.56 0.47 5.22

. .

. .

0.19

<0.01

0.68

. . . . . . .

. . .

0.48

051

. . . . . . . . . . . . . . . . . . . . .

0.32

0.55

. .

065 . . . . . . . .

. . .

. 064

. . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . .

'Evaluation without knowledge of treatments was performed by Roger Meads, Hortonville, WI. *Using the CATMOD procedure of SAS ( 4 4 ) , the probability that bST. university ( U ) , and the interaction of bST and U ( b S T x U ) affected cow health. 3Body condition score on a scale of 1 to 5 I1 = fat to 5 = thin (5011. 41ncludes abscesses or seromas on feet, legs, or hips; weak or inflamed fetlocks; weakness in scapular region; sore, puffy, or bad feet and legs; and redness in coronary band (only observed in cows a t the University of Kentucky). Does not include feet in need of trimming, posty, cow-hocked or sickle-hocked rear legs, winged shoulders, or crooked toes. 5Using Fisher's two-tailed exact test in the FREQ procedure of SAS (441, the probability that health of cows supplemented with 10.3, 20 6, or 41.2 mg/d of bST was different from that of cows supplemented with 0 mg/d of bST. 6Common relative risk (Mantel-Haensel) calculated using the FREQ procedure of SAS ( 4 4 ) to compare 0 versus 10.3, 20.6, or 41.2 mg/d of bST. 7Limits calculated using the 0.95 confidence intervals. 8Includes lameness, limping, reluctance to move, stifled joints, and tripping on toes. 9Includes light or enlarged quarters, quarters lost to mastitis, poor udder attachments, and broken suspensory ligaments. Journal of Dairy Science Vol. 79, No. 5, 1996

RESPONSES TO SOMATOTROPIN

incidence of ketosis, abomasal displacement, feet and leg problems, or the number of cows requiring antibiotic treatment for mastitis. Although somatic cell scores acquired from the DHIA were higher in cows supplemented with 41.2 mgld of bST, the mean score of 4 suggested that chronic infection was not a major problem. Evaluation of cows near the end of the experiment by a n independent consultant showed that cows supplemented with 10.3, 20.6, or 41.2 mg/d of bST did not have increased incidence of abnormal feet and legs, gait, or udders. Our observations should be interpreted cautiously, because no attempts were made to standardize diagnostic procedures, and cows were not critically evaluated for feet and leg problems, gait, udder conformation, or mastitis before they entered the treatment. In addition, we only had 34 cows per treatment. This number was sufficient to detect responses of production but might have been inadequate for identifying impacts of bST on reproduction and health. Data from other experiments ( 6 , 22, 24, 34, 41,471 support our conclusion t h a t indices of health and reproduction for cows supplemented with bST are similar to those for unsupplemented cows at similar milk production ( 6 , 22, 3 4 ) . Nevertheless, whether bST increases the incidence of mastitis or causes impairments in reproduction above that expected with higher milk production continues to be questioned. The suggestion by Burvenich e t al. ( 1 1 1 t h a t time to recover from mastitis is reduced in cows receiving bST warrants further investigation. CONCLUSIONS

Cows supplemented daily with bST beginning in early lactation produced more milk without effects on milk composition. Feed intake increased in response to additional milk production, and efficiency of milk production was improved. Cows supplemented with a high dose of bST ( 4 1 . 2 mgld) had reduced fertility, but fertility was not affected by lower doses ( 1 0 . 3 and 20.6 mgld). At 10.3 and 20.6 mgld of bST, impacts on cow health were not remarkable. REFERENCES 1 Annexstad, R. J., D. E. Otterby, J. G . Linn, W. P. Hansen, C. G. Soderholm, J. E. Wheaton, and R. G. Eggert. 1990. Somatotropin treatment for a second consecutive lactation. J. Dairy Sci. 73:2423. 2Armstrong, D. V., A. Burgos, J. A. Duque, and K. S.Madsen. 1990. Evaluation of the milk response of sometribove (recombinant methionyl bovine somatotropin) when administered to lactating dairy cows in commercial dairy herds in Arizona. J. Dairy Sci. 73!Suppl. l j : 1 6 0 . ( A b s t r . )

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a commercial dairy herd. J. Dairy Sci. 73(Suppl. 11: 160.(Abstr.) 22 Ferguson, J. D., and A. Skidmore. 1989. Bovine somatotropinreproduction and health. Page 57 in Advanced Technologies Facing the Dairy Industry: bST. Mimeo Ser. N o . 133, Cornell Coop. Ext., Cornell Univ., Ithaca, N Y . 23 Franson, S . E., W. J . Cole, R. G. Hoffman, V. K. Meserole, D. M. Sprick, K. S. Madsen, G. F. Hartnell, D. E. Bauman. H. H. Head, J. T. Huber, and R. C. Lamb. 1989. Responses of cows throughout lactation to sometribove, recombinant methionyl bovine somatotropin, in a prolonged release system: a dose titration study. Part I. Production responses. J. Dairy Sci. 72(Suppl. 1):451.(Abstr.) 24Galliga1-1, D. T., M. Kristula, C. R. Curtis, W. Chalupa, and D. W. Rock. 1990. Milk yield and reproduction of lactating cows SuDdemented with sustained release somatotrooin. J . Dairy ScI.' 73(Suppl. 1):198.(Abstr.) 25 Gibson. J . P.. B. W. McBride. J. H. Burton. J. L Burton. and R. W. Eggert. 1990. Effect on production traits of administration of rbST for up to three consecutive lactations J. Dairy Sci. 73(Suppl. 1):158.(Abstr.) 26 Hemken, R. W., R. J. Harmon, W. J. Silva, G. Heersche, and R. G. Eggert. 1988. Responses of lactating cows to a second year of recombinant bovine somatotropin ( b S T ) when fed two energy concentrations. J . Dairy Sci. 71(Suppl. 1):122.(Abstr.) 27 Huber, J. J., J. L. Sullivan, S . Willman, R. G. Hoffman, and G. F. Hartnell. 1990. Response of Holstein cows to biweekly sometribove ( S B ) injections for 3 consecutive lactations. J. Dairy Sci. 73:(Suppl. l):157.(Abstr.) 28Huber, J. T., S. Willman, K. Marcus, C. B. Theurer, D. Hard, and L. Kung, J r . 1988. Effect of sometribove ( S B ) , USAN (recombinant methionyl bovine somatotropin) injected in lactating cows a t 14-d intervals on milk yields, milk composition, and health. J. Dairy Sci.71(Suppl. 1):207.(Abstr.) 29 Jordan, D. C.. A. A. Aguilar, J. D. Olson, C . Bailey, G. F. Hartnell, and K. S. Madsen. 1991. Effects of recombinant methionyl bovine somatotropin (sometribove) in high producing cows milked three times daily. J. Dairy Sci. 74:220. 30 Kirchgebner, M., W. Schwab, and H. L. Muller. 1989. Effect of bovine growth hormone on energy metabolism of lactating cows in long-term administration. Page 143 in Energy Metabolism of Farm Animals. Y. van der Honing and W. H. Close, ed. Wageningen Univ., Wageningen, The Netherlands. 31 Lynch, G. L., T. H. Klusmeyer, M. R. Cameron, and J. H. Clark. 1991. Effects of somatotropin and duodenal infusion of amino acids on nutrient passage to the duodenum and performance of dairy cows. J. Dairy Sci. 74:3117. 32 Madakaze, C., R. H. Phipps, and D. L. Hard. 1990. Preliminary results on the influence of bovine somatotropin (sometribove) on milk Droduction in Zimbabwe. J. Dairv Sci. 73(SuouI. .. 1): 1 6 1.(A bs'tr . 33Mattos. W.. A. V. Pires. V. P. deFaria. J. D. Duaue. and K. S. Madsen. 1989. The 'effect of sometribove '(recombinant methionyl bovine somatotropin) on milk yields and milk composition in lactating dairy cows in Brazil. J. Dairy Sci. 72(Suppl. 1):452.(Abstr.) 34 McBride, B. W., J. L. Burton, and J. H. Burton. 1988. The influence of bovine growth hormone (somatotropin) on animals and their products. Res. Dev. Agric. 5:l. 35 McGuffy, R. K., R. P. Basson, and T. E. Spike. 1991. Lactation response and body composition of cows receiving somatotropin and three ratios of forage to concentrate. J. Dairy Sci. 74:3095. 36 National Research Council. 1989. Nutrient Requirements of Dairy Cattle. 6th rev. ed. Natl. Acad. Sci., Washington, DC.

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37 Palmquist. D. L. 1988. Responses of high-producing cows given daily injections of recombinant bovine from d 30 to 296 of lactation. J. Dairy Sci. 7liSuppl 1):206,tAbstr.) 38 Peel, C. J., and D. E. Bauman. 1987. Somatotropin and lactation. J . Dairy Sci. 70:474. 39 Peel, C. J., D. L. Hard, K. S . Madsen. and G. de Kerchove. 1989. Bovine somatotropin: mechanisms of action and experimental results from different world areas. Page 9 in Meeting the Challenges of New Technology. Monsanto Tech. Symp. preceding Cornell Nutr Conf. Anim. Sci. DIV..Monsanto Agric. Co., St. Louis, MO. 40Pee1, C. J.. L. D. Sandles. K. J. Quelch. and A. C. Herington. 1985. The effects of long-term administration of bovine growth hormone on the lactational performance of identical twin dairy cows. Anim. Prod. 41:135 41 Phipps. R. H. 1989. A review of the influence of somatotropin on health, reproduction and welfare in lactating dairy cows Page 88 in Use of Somatotropin in Livestock Production. K. Sejrsen, M. Vestergaard, and A. Neimann-Sorensen. ed. Elsevier Appl. Sci., New York, NY. 42 Phipps, R. H., R. F. Weller, N. Craven, and C. J . Peel. 1990. Use of prolonged-release bovine somatotropin for milk production in British Frieson dairy cows. I. Effect on intake, milk production and feed efficiency in two consecutive lactations of treatment. J. Agric. Sci. ( C a m b . ) 115:95. 43 Robinson, P. H., G. de Boer, and J . J Kennelly. 1991. Effect of bovine somatotropin and protein on rumen fermentation and forestomach and whole tract digestion in dairy cows. J. Dairy Sci. 74:3505. 44SAS" Users Guide: Statistics, Version 5 Edition. 1985. SAS Inst., Inc., Cary, NC. 45Sechen, S. J., D. E. Bauman, H. F. Tyrrell, and P. J. Reynolds. 1988. Effect of somatotropin on kinetics of nonesterified fatty acids and partition of energy, carbon. and nitrogen in lactating dairy cows. J. Dairy Sci. 72:59. 46Soderholm, C. G., D. E. Otterby, J. G. Linn, F. R. Ehle. J. E. Wheaton, W. P. Hansen, and R. J. Annexstad. 1988. Effects of recombinant bovine somatotropin on milk production. body composition, and physiological parameters. J. Dairy Sci. 71:355. 47Thomas, C., I. D.Johnnson, W. J. Fisher, G. A. Bloomfield, S.V. Morant, and J. M. Wilkinson. 1987. Effect of somatotropin on milk production, reproduction and health of dairy cows. J. Dairy Sci. 69(Suppl. 1):175.(Abstr.j 48Thomas, J. W., R. A. Erdman, D. M. Galton, R. C. Lamb, M. J. Arambel, J. D.Olson, K. S. Madsen, W. A. Samuels. C. J. Peel. and G. A. Green. 1991. Responses by lactating cows in commercial dairy herds to recombinant bovine somatotropin. J. Dairy Sci. 74:945. 49Tyrrel1, H. F., A.C.G. Brown, P. J. Reynolds, G. L. Haaland. D. E. Bauman, C . J. Peel, and W. D. Steinhour. 1988. Effect of bovine somatotropin on metabolism of lactating dairy cows: energy and nitrogen utilization as determined by respiration calorimetry. J. Nutr. 118:1024. 50Wildman, E. E., G. M. Jones, P. E. Wagner, R. L. Bowman, H. F. Trout, J r . , and T. V. Leach. 1982. A dairy cow body condition scoring system and its relationship to selected production characteristics. J. Dairy Sci. 65:495. 51 Winsryg, M. D., M. J. Arambel, B. A. Kent, and J . L. Walters. 1991. Effect of sometribove on rumen fermentation, rate of passage, digestibility, and milk production responses in dairy cows. J. Dairy Sci. 74:3518.