Response of Brazilian crossbred cows to varying doses of bovine somatotropin.

The effect of n-methionyl bovine somatotropin (bST) on milk yield was evaluated in crossbred cows (40 1/2 Bos indicus x 1/2 Bos taurus and 18 1/4 B. indicus x 3/4 B. taurus) in Brazil. Cows were randomly assigned to treatments within stage of lactation [stage 1 = 56 to 100 d in milk (DIM); stage 2 = 101 to 199 DIM] and breed groups (1/2 vs. 1/4 B. indicus blood). Treatments were 250 or 500 mg of bST administered every 14 d. Cows in the control group did not receive bST or a placebo. Treated cows received bST injected subcutaneously in the postscapular region, alternating between the left and right sides. The 26-wk experiment consisted of 2 wk of pretreatment and 24 wk of treatment. Cows were housed in an open lot with regulated access to pasture. Cows were milked twice daily and scored for body condition at 2-wk intervals. Compared with controls, milk yield increased equally (22%) for cows receiving 250 or 500 mg of bST. Milk yield response to bST was higher and persisted longer during stage 1 of lactation than during stage 2 of lactation. No difference in response to bST was noted between cows with 1/2 or 1/4 B. indicus blood. Cows treated with 500 mg of bST tended to have more mastitis, but no other adverse health effects were observed. The potential use of 250-mg doses of bST at 14-d intervals in crossbred cattle in Brazil and other subtropical regions throughout the world is suggested, particularly before about 220 DIM.

Effects of a prolonged-release formulation of sometribove (n-methionyl bovine somatotropin) on Jersey cows.

Milk production, feed efficiency, health, and reproduction were evaluated in 46 Jersey cows that received either 500 mg of sometribove (n-methionyl bST) in a prolonged-release formulation or an equivalent volume of excipient bi-weekly beginning at 60 +/- 3 DIM. Cows were fed a TMR for ad libitum intake and were milked twice daily. Treatment with sometribove increased 3.5% FCM production 5.3 kg/d (31.4%) over controls. Milk composition was not changed, except that milk P content averaged 51 ppm higher in bST-treated cows. Net energy intake was 4.8 Mcal/d (22.9%) higher in the bST-treated cows than in the controls. General health of all cows was good throughout the study, but the cows treated with bST had more cases of mastitis than did the control cows. The bST treatment produced localized reactions at the site of injection in some cows, but these reactions did not affect milk production. Sometribove treatment had no effect on reproductive performance; 85% of the treated and 100% of the control cows calved successfully. Treatment with bST for a full lactation did not affect performance during the initial 60 d of the subsequent lactation.

Insulin binding to liver microsomes from lean and obese swine during growth to market weight.

Insulin binding to liver microsomes from lean (Yorkshire) and obese (Ossabaw) swine was measured at four different times during growth to market weight. Over the physiological range of insulin, binding decreased during growth to market weight in Yorkshire swine. This was not observed for Ossabaw swine. When comparisons of insulin binding were made between lean and obese swine of a similar age, microsomes from lean swine bound more insulin over the physiological range of insulin than microsomes of obese swine. This difference was also observed when comparisons were made at similar live weights. The dissociation constant (Kd) for the high affinity receptor population increased with growth in both breeds indicating that binding affinity was decreasing. Over the physiological range of insulin, binding affinity was lower for liver microsomes of obese swine vs liver microsomes from lean swine when comparisons were made at a similar age. These results suggest that the liver of obese swine is moderately insensitive to insulin and that binding of insulin to liver from lean swine declines during growth to market weight.

Temporal nature of insulin binding and insulin-stimulated glucose metabolism in isolated swine adipocytes.

Insulin binding and insulin-stimulated glucose metabolism were measured in swine adipocytes isolated from adipose tissue obtained by biopsy on 4 successive days. These characteristics were also measured in adipose tissue obtained on the 5th d immediately after exsanguination. Binding of 125I-insulin was measured at three different concentrations of unlabeled insulin (0, 1, 100 ng/ml) on each day. Specific binding (pg bound . 2 X 10(5) adipocytes-1 X 90 min-1) was not different (P greater than .05) for each insulin concentration among the 5 d. Specifically bound insulin increased (P less than .05) with increasing insulin concentration. The effects of insulin (0, 1, 100 ng/ml) on glucose oxidation and glucose conversion to lipid were also examined in biopsy (B) and postmortem (PM) adipocytes. For a respective insulin concentration, there was no difference in glucose oxidation or lipid synthesis over the 5-d (four B, one PM) sampling period. Lipid synthesis was stimulated by the presence of insulin (P less than .05; 1 and 100 ng/ml) when compared with basal incubations; however, glucose oxidation was unaffected by the presence of insulin. There was no difference in lipid synthetic rates between 1 and 100 ng/ml of insulin. The responsiveness of glucose oxidation and lipid synthesis to insulin in PM samples was identical to that for adipocytes from B samples. These results indicate: 1) that glucose metabolism and insulin binding to adipocytes isolated from swine adipose tissue obtained by biopsy did not differ from that in tissue samples obtained shortly after death and 2) that insulin-stimulated glucose metabolism and insulin binding did not fluctuate appreciably over a 5-d period when adipose tissue was obtained at the same time each day.