Superovulatory response of one ovary is related to the micro- and macroscopic population of follicles in the contralateral ovary of the cow

We hypothesized that the ovulatory response of one ovary to FSH would be re lated positively to the size of the primordial and growing pools of follicl es in the other ovary. Nonlactating cows (n = 26) were unilaterally ovariec tomized and 2 days later were superovulated. The superovulatory response wa s classified as Low (< 5 corpora lutea [CL]), Medium (5-14 CL), or High (> 14 CL), Surface follicles on the ovary removed before superovulation were c lassified as small (1-3 mm), medium (3-7 mm), or large ( > 7 mm), and the o vary was then fixed and serially sectioned. Follicles less than or equal to 1 mm in diameter in 388 +/- 38 fields (2 x 2 mm) per cow were classified a s primordial, primary, secondary, or tertiary. By classification, Suboptima l ovaries contained < 100 follicles less than or equal to 1 mm and Optimal ovaries contained > 250 follicles less than or equal to 1 mm. Number of CL was correlated positively with total number of primordial, tertiary, and me dium surface follicles. Number of Empty fields (2 x 2-mm fields containing no follicles) was correlated negatively with superovulatory response and nu mber of primordial follicles. Number of CL was related to number of tertiar y follicles in a positive linear manner and the number of medium follicles in a positive quadratic manner (r(2) = 0.66). Numbers of primordial, tertia ry, small surface follicles, medium surface follicles, and total surface fo llicles were lower (p less than or equal to 0.06) in the Low superovulatory response group than in the Medium or High group. Suboptimal ovaries had fe wer small surface follicles and fewer CL than Optimal ovaries (p < 0.05). W e conclude that superovulatory response in cattle is related positively to the pools of primordial and growing follicles in the bovine ovary.