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 (>or=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.