Responses of Dairy Cows in Early Lactation to Bovine Somatotropin and Ruminally Inert Fat1 P. L. SCHNEIDER Real Veal, Inc. Ixonia, WI 53036

D. SKLAN Faculty of Agriculture Hebrew University POB 12 Rehovot 76-100. Israel D. S.

KRONFELD Virginia Tech Blacksburg 24061

W. CHALUPA SChool of Veterinary Medicine University of Pennsylvania New Bolton Center Kennett Square 19348. ABSTRACT

dietary fatty acids; and C18:1 fatty acids were higher with either bST or dietary fatty acids. Blood acetoacetate concentrations were higher with both bST and dietary fany acids. p-hydroxybutyrate was not different, and FFA and insulin concentrations increased with bST. In this experiment. the energy supplied by CaLCFA acids enhanced the lactogenic effect of bST. (Key words: dairy cattle. somatotropin, ruminally inert fat)

Bovine somatotropin (0 or 41.2 mg/d bST) and calcium salts of long-chain fatty acids (0 or .77 kg/d Ca-LCFA) were administered to 16 Holstein cows in early lactation. Cows remained on 0 or 41.2 mg/d bST for the entire 10 wk and received 0 or .77 kg/d Ca-LCFA in one of two 5-wk periods. Production data were recorded daily, milk fany acids, and blood metabolites were determined once each period. Treatments did not affect feed intake. Fat-corrected milk (kg/d) and percentage of milk fat for cows receiving no supplementation, fany acids alone, bST alone, and fatty acids and bST together were 33.8, 3.2; 33.5, 3.1; 37.4, 3.4; and 40.8, 3.5. Milk fatty acids below C 16 were reduced with either bST or dietary fatty acids; C16 fatty acids were lower with bST but higher with dietary fatty acids; C 18:0 fatty acids were reduced with

INTRODUCTION

Received July 26. 1989. Accepted November 27.1989. lThis study was supponed in part by the US-Israel Binational Agricultural Research and Development Fund, USDA Section 1433 Formula Funds for Research and Animal Health, Church and Dwight Co.• Inc. Princeton. NJ 08480 and American Cyanamid Co. Princeton, NJ 08540.

1990 J Dairy Sci 73:1263-1268

Forty-five to 70% of US dairy producers may adopt use of recombinantly derived bST by 1996 (10). University studies have shown major increases in milk production from administration of bST in a dose-dependent fashion ranging from 2 to 7 kg/d (I, 5, 7). Meeting the energy requirements for high producing cows in early and peak lactation has always been a challenge, and increasing energy density of the ration is the accepted practice. Although cows increase their feed intake when treated with bST (6, 15), energy balance may remain negative until wk 7 to 10 of treatment (1, 2). Commencing bST treatment in early lactation may extend the time that these cows are in negative energy balance.

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Greater energy intake can be achieved by formulating diets with higher percentages of grain or by including rurrjnally inert fats such as saturated LCFA or Ca-LCFA (8, 9, II, 14, 18). Increasing the percentage of grain may compromise fiber intake, which can result in various digestive and metabolic disorders (14). Incorporation of dietary LCFA directly into milk fat is more efficient than de novo synthesis of fatty acids by the mammary gland (11). Dietary LCFA may decrease the risk of ketosis by reducing the need to mobilize LCFA from adipose tissue. Furthermore, energy deficiency may increase the days to first estrus, decrease conception rate, and lengthen the calving interval (4). The objective of this experiment was to determine the responses of dairy cows in early lactation to bST and ruminally inert fat. MATERIALS AND METHODS

Sixteen multiparous Holstein cows from the University of Pennsylvania dairy research herd were randomly assigned at 2 wk postpartum to either a 0 or 41.2 mg/d treatment of bST (Recombinant Bovine Somatotropin, American Cyanamid Co., Princeton, NJ). Animals remained on this treatment for the duration of the experiment. In addition, each cow received either 0 or .77 kg/d Ca-LCFA (MEGALAc® Rumen By-

pass Fat, Church and Dwight Co. Inc., Princeton, NJ) for one of two 5 wk periods in a single reversal design. Diets were fed twice daily as a total mixed ration. Administration of bST started at wk 2 postpartum, adaptation to diets started at wk 3, and the experiment started at wk 4. There was an additional week between periods for adjustment to diet change. Feed intake and milk production were recorded daily. Milk from an a.m. and p.m. milking was sampled 1 d each week and pooled. Blood was sampled from the caudal artery every week at about 1300 h for acetoacetate analysis. Blood sampled in the last week of each period was also analyzed for ~-hydroxy­ butyrate, FFA, insulin (Serono Diagnostics, Inc., Norwell, MA), and bST (American Cyanamid Company, Princeton, NJ, courtesy of Carl Simkins). Data was analyzed by method of least squares analysis of variance using general linear model procedures of SAS (17) with bST, cow(bST), Ca-LCFA, period, bST x Ca-LCFA, and bST x period as sources of variance. Differences between treatments were examined by single degree of freedom orthogonol contrasts. RESULTS

Composition of diets is presented in Table 1. Dietary DM consisted of approximately 35% forage and 65% concentrate. The laboratory

TABLE 1. Composition of diets. I Ingredient

Control

Com silage Soybean meal Ground ear com Distillers grains Megalac3 Molasses Limestone Dicalcium phosphate Monosodium phosphate Trace-mineral salt Sodium bicarbonate Magnesium oxide Selenium Vitamin A,D, and E premix Potassium chloride

35.1 14.6 37.5 8.4

Ca-LCFA2 (%)

1.0 1.50 .25 .46 .92 .25 .10 .05 .10

34.9 15.5 33.7 8.3 3.5 1.0 .60 .20 .46

.92 .25 .10 .05 .10

I Dry matter basis. 2Calcium salts of long-ehain fany acids. 3Fatty acid analysis of Megalac (%) CI6 56.2; C1S:O, 4.1; C1S: 1, 33.3; CIS:2' 6.0; C\S:2, .4. Journal of Dairy Science Vol. 73.

No.5. 1990

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SOMATOTROPIN AND RUMINALLY INERT FAT TABLE 2. Analysis of diets. Component

Ca-LCFA 1

Control

- - - - (%) - - - -

Crude protein By-pass protein 2 ADF Ca P Mg NEt. Mcal/kg EE. %3

15.9 5.9 2\.4 .55 .31 .34 \.63 5.2

15.6 5.8 22.1 .62 .39 .37 \.79 7.4

I Calcium salts of long-chain fatty acids.

2Calculated value. 3Ethcr extract; 10% glacial acetic acid was added to ether during ether extract procedure to dissociate calcium salt.

analysis of the diets is Table 2. Diets were balanced for by-pass protein, and Ca was equalized in all treaunents. Feed intake was not significantly affected by either bST or dietary Ca-LCFA (Table 3). This may have been due to the shortness of periods. Feed intake tended to increase within a few weeks of bST supplementation in longer experiments 0, 2, 16). Cows receiving bST produced more 3.5% FCM than unsupplemented cows (Table 3). Supplementation of Ca-LCFA without bST did not affect 3.5% FCM, milk yield, or milk fat percentage. Apparent feed efficiency increased with bST and increased even funher with both bST and Ca-LCFA. The interaction of bST and Ca-LCFA indicated that

Ca-LCFA was needed to maximize the response to bST. Energy intake was greater with Ca-LCFA (Table 4). Milk energy secretion tended to increase with bST and was highest for cows receiving bST and Ca-LCFA. Energy balance was lowest for cows receiving bST and CaLCFA. Efficiency of milk production based on net energy and corrected for body weight gain or loss was greater with bST but was not affected by Ca-LCFA supplementation. Proportions of milk fatty acids with chain lengths less than CI6 were lower with CaLCFA (Table 5). Proportions of palmitic acid were not affected by Ca-LCFA treaunent alone. With bST, however, Ca-LCFA supplementation significantly raised proportions of palmitic acid. Stearic acid decreased with Ca-LCFA and oleic acid increased with both bST and CaLCFA. Concentrations of metabolites in plasma are in Table 6. Acetoacetate was increased by bST and Ca-LCFA together, but ~-hydroxybutyrate was not significantly different. Free fatty acid and insulin concentrations increased with bST. Acetoacetate decreased as lactation progressed (between periods 1 and 2); however, acetoacetate concentration for bST and CaLCFA together was higher than any other treatment with values of 1.80 mg/lOO ml for period I and .56 mg/IOO ml for period 2. DISCUSSION

The combination of bST and Ca-LCFA resulted in a synergistic enhancement of 3.5%

TABLE 3. Production data.

o mgld

bST

Production Feed intake. kgld 3.5% FCM. kgld Apparent feed efficiency 3 Milk. kgld Milk fat. % Milk protein. %

41.2 mgld bST

.77 kgld Ca-LCFA Ca-LCFA

o kgld

23.1 33.8 g

22.1 33.5 g

22.2 37.4h

2\.9 40.8 h

\.49a 36.0g 3.2gh 2.8

1.52" 35.7 g 3.1 g 2.8

1.69b 38.4 h 3.4gh 2.8

\.91 C 41.1 i 3.5 h 2.8

o kgld

Significance (P)

.77 kgld Ca-LCFA Ca-LCFA

bST x Ca-LCFA Ca-LCFA

SEM

.76 .03

.23 .28

.47 .21

.50 1.35

Responses of dairy cows in early lactation to bovine somatotropin and ruminally inert fat.

Bovine somatotropin (0 or 41.2 mg/d bST) and calcium salts of long-chain fatty acids (0 or .77 kg/d Ca-LCFA) were administered to 16 Holstein cows in ...
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