Nitrogen Balance of Gilts as Affected by Protein Intake and Stage of Gestation 1'2

The effects of four levels of crude protein (CP) and stage of gestation on the growth, reproductive performance and N balance of 64 crossbred gilts were examined in two trials. Gilts were fed 147, 256, 309 or 369 g of CP daily in trial 1 and 119 ,227 ,275 or 326 g/d in trial 2. Total body weight gain and average daily gain (ADG) were not significantly affected by protein intake, although the quadratic effect on ADG approached significance (P<.I). Both total body weight gain and ADG increased linearly (P<.01) as stage of gestation progressed. Gilts were slaughtered at 30, 60 or 90 d of gestation and reproductive performance was evaluated. Protein intake did not significantly affect numbers of corpora lutea or live embryos, survival rate or embryo length. But survival rate (P<.05), number of corpora lutea (P<.05) and live embryo numbers (P<.01) declined linearly as gestation stage progressed. Embryo length increased linearly (P<.05) as stage of gestation progressed. Nitrogen balance studies were conducted before breeding and in early, mid and late gestation. Significant trial • protein level x collection period interactions existed. In trial 1, N retention increased linearly (P<.01) as dietary protein increased. Retention increased (P<.01) by 4.1 g/d from prebreeding to early pregnancy. Stage of gestation had a quadratic effect on retained N; retention was higher in early and late gestation than in mid-gestation. In trial 2, mean N retention during pregnancy