Growth, reproductive performance and nitrogen balance of gilts as affected by protein intake and stage of gestation.

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 less than .1). Both total body weight gain and ADG increased linearly (P less than .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 less than .05), number of corpora lutea (P less than .05) and live embryo numbers (P less than .01) declined linearly as gestation stage progressed. Embryo length increased linearly (P less than .05) as stage of gestation progressed. Nitrogen balance studies were conducted before breeding and in early, mid and late gestation. Significant trial x protein level x collection period interactions existed. In trial 1, N retention increased linearly (P less than .01) as dietary protein increased. Retention increased (P less than .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 was -1.7 g/d. Retention was not significantly affected by protein intake but retained N declined quadratically (P less than .05) with stage of gestation to a -16.3 g/d at d 90. In contrast with trial 1, pregnancy did not result in an increase in retention of N. A relationship between protein intake and N balance data and resulting reproductive performance could not be established. The lowest levels of protein intake (147 and 119 g/d in trials 1 and 2, respectively) appeared to be adequate for the first 90 d of gestation in the gilt. However, N retention was not maximized at this protein intake.