Ovarian follicular populations at two stages of an estrous cycle in heifers given high energy diets.

Sixteen crossbred heifers were assigned at random on d 3 of an estrous cycle to continue to receive the medium quality hay (control diet) or to be flushed with a grain ration (high-energy diet) until slaughtered on d 12 or 16. The ovarian follicles were counted and measured using routine histological techniques. Both the nonatretic and atretic (more than four pyknotic bodies) antral follicles (greater than .14 mm) were separated into six classes according to diameter size. The mean number of nonatretic follicles measuring .29 to .67 mm and .68 to 1.57 mm in heifers on a high-energy diet increased from 30.8 and 8.1 on d 12 to 57.5 and 15.5 on d 16, whereas in heifers on a control diet it decreased from 43.1 and 13.0 to 28.1 and 6.5, respectively (energy in diet X day of estrous cycle interaction, P less than .05). The mean number of nonatretic follicles measuring 3.68 to 8.56 mm decreased from 2.1 to 0 between d 12 and 16 in heifers on a high-energy diet while it remained the same at 0 and .5, respectively, for heifers on a control diet (energy in diet X day of cycle interaction, P less than .05). Of the total number of follicles (mean = 161) 38.2% were atretic. Mean number of atretic follicles measuring 1.58 to 3.67 mm in heifers on a high-energy diet increased from 14.8 at d 12 to 31.0 at d 16 whereas in heifers on a control diet it decreased from 27.4 to 13.3, respectively (energy in diet X day of cycle interaction, P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)