Bovine model of reproductive aging: Response to ovarian synchronization and superstimulation

The responsiveness of the hypothalamo-pituitary axis to steroid treatments for ovarian synchronization and the ovarian superstimulatory response to exogenous FSH was compared in 13–14 year old cows and their 1–4 year old young daughters. We tested the hypotheses that aging in cattle is associated with: (1) decreased follicular wave synchrony after estradiol and progesterone treatment; (2) delayed LH surge and ovulation in response to exogenous preovulatory estradiol treatment; (3) reduced superstimulatory response to exogenous FSH. Higher plasma FSH concentrations (P < 0.01), and a tendency (P = 0.07) for fewer 4–5 mm follicles at wave emergence were observed in old cows (n = 10) than in young cows (n = 9). The suppressive effect of estradiol/progesterone treatment on FSH was similar between old and young cows. Although the preovulatory LH surge in response to estradiol treatment was delayed in old than young cows (P = 0.01), detected ovulation times were not different. No difference in ovarian superstimulatory response was detected between age groups, but old cows (n = 8) tended (P = 0.10) to have fewer large follicles (≥9 mm) 12 h after last FSH treatment than in young cows (n = 7). We concluded that pituitary and ovarian responsiveness to estradiol/progesterone synchronization treatment was similar between old and young cows, but aging was associated with a delayed preovulatory LH surge subsequent to estradiol treatment. Old cows tended to have fewer large follicles after superstimulatory treatment than young cows.