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)