Interrelationships between dietary protein level, energy intake, and nitrogen retention in pregnant gilts

Two experiments were conducted to study the effects of dietary protein levels and DE intake on N retention in pregnant gilts. Thirty-two gilts were used in Exp. 1 to investigate the response to eight levels of dietary CP ranging from 50 to 235 g/kg (3.3 to 14.5 lysine/kg). Gilts were given 1,400 g of feed daily throughout pregnancy; diets contained similar balances of amino acids and similar amounts of DE (3.60 to 3.63 Mcal/kg). Thirty gilts in Exp. 2 were allocated during pregnancy to six levels of feeding ranging from 1.1 to 3.1 kg/d. The common diet given to gilts contained 3.49 Mcal of DE/kg, 155 g of CP/kg, and 10.7 g of lysine/kg and was considered adequate in protein. Nitrogen balance trials were conducted during early, mid-, and late pregnancy and collection periods of 5 d duration commenced on d 30, 58, and 86 in Exp. 1 and d 30, 58, and 93 in Exp. 2. The average live weights of pigs on all treatments within each collection period were similar and were 112.5, 123.3, and 136.6 kg and 120.7, 136.3, and 158.3 kg in Exp. 1 and 2, respectively. At each stage of pregnancy increments of dietary protein increased N retention up to an inflection point, after which N retention remained at a constant level. The maximum rates of N retention, 10.0, 12.1, and 16.5 g/d during early, mid-, and late pregnancy, occurred at 142, 133, and 162 g of CP/kg, respectively; the corresponding dietary lysine:DE values were 2.4, 2.3, and 2.7 g of lysine/Mcal of DE.(ABSTRACT TRUNCATED AT 250 WORDS)