DELAY IN EMERGENCE OF THE OVULATORY FOLLICULAR WAVE IN OLD MARES

The characteristics of the prim follicular wave (wave that gives origi n the ovulatory follicle associated with estrus) were compared during an interovulatory interval among 3 groups of pony mares aged 5 to 7 ye ars (n=9),15 to 19 years (n=10), and greater-than-or-equal-to 20 years (n=11). Significant increases in the diameters of 6 largest follicles , excluding the dominant follicle, were used to detect the emergence o f follicular-waves, Emergence of the primary wave occurred later (P<0. 05) in the oldest group (mean +/-sem: 10.8+/-0.9 days after ovulation) than in the 2 younger groups (7.7+/-0.7 and 7.3+/-1.1 days). In addit ion, in the oldest group, fewer (P<0.05) of the 6 evaluated follicles were considered to be part of the primary wave (4.6+/-0.5, 4.8+/-0.4, and 2.8+/-0.3 follicles for youngest to oldest groups). No other signi ficant age-associated differences in the characteristics of the primar y wave were found. In a previous study, no differences in mean FSH con centrations were found between mares aged 15 to 19 years and mares age d greater-than-or-equal-to 20 years. The defect in the old mares, ther efore, apparently involved the ovaries (follicles deficient in numbers or in responsiveness to FSH), rather than availability of FSH.