Nitrogen requirement of pregnant gilts.

Eleven Yorkshire x Landrace gravid gilts were used in two Latin square trials to determine the N requirement for pregnancy. Semipurified diets were formulated to be adequate in indispensable amino acids (IAA) and other nutrients. Diets were fed once daily (1.82 kg); L-glutamic acid, corn sugar, powdered cellulose, and soybean oil percentages differed to maintain isocaloric diets. In Trial 1, six gilts were fed diets containing 6.6 to 17.2% CP equivalent (19.2 to 50.1 g of N/d) during six 10-d periods beginning on d 40 postcoitum. In Trial 2, five gilts were fed diets containing 4.3 to 12.6% CP equivalent (12.5 to 36.8 g of N/d) during five 10-d periods beginning on d 50 postcoitum. Nitrogen balance trials were conducted during the last 5 d of each period. Blood samples were taken both before and 3 h after the last feeding of each period. Results from Trial 1 suggested that adequate N retention (10 g/d) could be attained by pregnant gilts fed less than 28 g of N/d intake when the diet contained indispensible amino acids at levels suggested by Nutrient Requirements of Swine (NRC, 1988). An intake of 20.6 g of N/d (7.1% CP equivalent) yielded near maximum N retention among pregnant gilts fed the semipurified diets in Trial 2. Other criteria measured (urine urea nitrogen and plasma urea nitrogen) had limited value in the evaluation of the N status of the pregnant gilts in these trials.