DELAY IN EMERGENCE OF THE OVULATORY FOLLICULAR WAVE IN OLD MARES

The characteristics of the prim follicular wave (wave that gives origin the ovulatory follicle associated with estrus) were compared during an interovulatory interval among 3 groups of pony mares aged 5 to 7 years (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 of 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 addition, 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 significant age-associated differences in the characteristics of the primary wave were found. In a previous study, no differences in mean FSH concentrations were found between mares aged 15 to 19 years and mares aged greater-than-or-equal-to 20 years. The defect in the old mares, therefore, apparently involved the ovaries (follicles deficient in numbers or in responsiveness to FSH), rather than availability of FSH.