Effects of dietary energy intake by gilts and heat stress from days 3 to 24 or 30 after mating on embryo survival and nitrogen and energy balance.

Bred gilts were used in two experiments (n = 140) to study the interaction and main effects of dietary energy intake and heat stress on embryo survival and nitrogen (N) and energy balance from d 3 to slaughter on d 30 (Exp. 1) or d 24 (Exp. 2) after mating. In both experiments, the ME treatments were 5.4 or 8.1 Mcal of ME/(gilt.d). Temperatures were either a constant thermoneutral of 23 +/- 1 degrees C or a heat stress regimen, making four treatments in a 2 x 2 factorial arrangement. Gilts were allotted directly to one of the treatments on d 3 after mating. In Exp. 1, the 24-h cyclic heat stress regimen consisted of an increase from 25 degrees C at 0800 to 34 degrees C at 1400, 34 degrees C from 1400 to 1700, then a decline to 25 degrees C at 2000, with 25 degrees C until 0800. In Exp. 2, heat stress was constant at 33 +/- 1 degrees C. No energy x temperature treatment interactions occurred (P > .2 to .8) for the variables measured in Exp. 1 and 2. Heat stress reduced (P < .05 or .01) diet and ME intake/day, ME retained/day, and ME/GE compared with the thermoneutral controls in Exp. 1 and 2. Heat stress reduced (P < .05) N digestibility in Exp. 1 and reduced (P < .01) N retained/day and N retention/N intake in Exp. 2. Rectal temperature and respiration rate were increased (P < .01) by heat stress in Exp. 1 and 2.(ABSTRACT TRUNCATED AT 250 WORDS)