The effect of exogenous somatotropin on lactation performance of first-litter sows.

To determine the effect of exogenous porcine somatotropin (ST) on lactation performance of sows, 24 first-litter sows were injected daily at 0800 with either 10 mg of recombinant ST or an equivalent volume of buffer between d 8 and 39 of lactation. Litter size was standardized to six (n = 2), seven (n = 8), eight (n = 6), or 10 (n = 8) pigs within each pair of sows by fostering pigs within a few days after parturition. Milk yield and composition of sows given ST was similar at all stages of lactation to that of control sows. Combining treatment data revealed that the milk yield of sows was related linearly (P < .01) to litter size and was described with the following equation: MY = 1.03 (+/- .71) + .899 (+/- .102) LS (n = 24, r2 = .78), where MY is average milk yield (kilograms/day) of sows over 4 to 7, 11 to 14, 18 to 21, 25 to 32, and 32 to 39 d of lactation and LS is number of pigs in the litter. The body temperature of sows increased (P < .05) in response to administration of ST. Plasma IGF-I and glucose were increased (P < .05) by ST, but plasma urea concentrations were lower (P < .05) in ST-treated sows. Sows treated with ST lost more backfat (P < .05) during lactation, but neither voluntary feed intake nor body weight loss was significantly (P > .05) affected by ST. These data indicate that a 10-mg daily injection of ST from d 8 to 39 of lactation alters metabolism but does not increase milk production in lactating first-litter sows.

The response of first-litter sows to dietary protein level during lactation.

Thirty-six sows were used to study responses of milk production, milk composition, and N balance to six concentrations of dietary CP ranging from 63 to 238 g/kg (4.4 to 15.1 g of lysine/kg) during the first lactation. Sows, on average, were 149.3 kg live weight and had 26.1 mm of back fat at P1 (which is 45 mm from the midline at the level of the last rib) immediately after parturition. During lactation, all sows suckled nine pigs each and were offered up to 4,000 g of feed daily; diets contained similar balances of amino acids and similar amounts of DE (3.56 to 3.63 Mcal/kg). Nitrogen balance trials were conducted during early and late lactation and 5-d collection periods commenced on d 10 and 24 of lactation, respectively. During both periods of lactation, there were significant positive linear relationships between the level of dietary protein and milk yield and contents of fat and total solids in milk. Milk yield increased from 7.79 to 9.91 kg/d and from 7.02 to 8.90 kg/d, whereas total solids in milk increased from 199 to 225 g/kg and from 202 to 228 g/kg during early and late lactation, respectively, in response to increasing level of dietary protein from 63 to 238 g of CP/kg. A two-phase linear regression model used to describe the relationship between N balance and dietary CP level established that sows required a diet containing > or = 202 g of CP/kg or 12.8 g of lysine/kg to maximize N balances during both stages of lactation.(ABSTRACT TRUNCATED AT 250 WORDS)