Influence of short-term fasting during the luteal phase of the estrous cycle on ovarian follicular development during the ensuing proestrus of ewes

Short-term fasting of mature ewes during diestrus results in increased serum concentrations of progesterone and a delayed pre-ovulatory surge release of LH. To determine if these changes in reproductive hormones influence subsequent follicular development, mature ewes observed in estrus were assigned randomly to control (n = 10) or fasted (n = 15) groups. Control ewes had ad libitium access to feed, whereas fasted ewes were not fed from day 7 through 11 of their estrous cycle. Daily blood samples were collected from control and fasted ewes throughout the fasting period. Fasting increased (P < 0.001) serum concentrations of progesterone (4.4 ng/mL versus 2.7 ng/mL [±0.3]). On day 12, all ewes were treated with 10 mg of PGF2α and fasted ewes were returned to ad libitum feed. Ovaries were collected from ewes (n = 5 each group) at 0 and 72 h following PGF2α in control and 0, 72 and 96 h in fasted ewes. Ovaries were weighed and small (≤2 mm), medium (3–4 mm), and large (≥5 mm) follicles were enumerated. Total numbers of follicles were less (P < 0.001) in fasted than fed ewes (14.6 versus 30.2 [±2.2]) at 0 h, but did not differ (P = 0.9) when numbers of follicles were compared at similar times before the anticipated LH surge (i.e., at 72 h versus 96 h in control and fasted ewes, respectively). Within follicular size class, numbers of small and medium follicles were decreased (P = 0.04) at 0 h in fasted ewes. Numbers of large follicles did not differ (P = 1.0) between groups. Although numbers of small and medium ovarian follicles in fasted ewes recovered by 96 h to values comparable to fed ewes at 72 h following PGF2α, serum concentrations of estradiol 17β (P = 0.08) and FSH (P = 0.06) tended to be decreased in fasted ewes before the anticipated surge release of LH. Pituitary content of LH and FSH also tended to be lower (P ≤ 0.09) at 96 h in fasted ewes than at 72 h in control ewes, but did not differ (P ≥ 0.4) at hour 0 following PGF2α. Hypothalamic and stalk median eminence contents of GnRH were not influenced (P ≥ 0.2) by fasting at any time period. Fasting during the luteal phase perturbs gonadotropin secretion and may influence fertility by causing a delay in ovarian follicle development.