Alterations in follicular function associated with selection on ovulation rate in Finn ewes

Finn ewes have been selected on ovulation rate to produce three lines with approximate ovulation rates of 5 (High), 3 (Control), and 2.5 (Low). The associated alterations in follicular function were investigated in three experiments. The function of large estrogenic follicles (Exp. 1) was assessed by measuring in vitro output of steroids and inhibin after a 1-h culture period. Follicles from High line ewes contained fewer (P < .01) granulosa cells than follicles from Low line ewes. Estradiol output per granulosa cell and testosterone output per thecal cell were greater for High than for Low line follicles (P < .01 and < .05, respectively). In contrast, inhibin output, expressed per follicle or per granulosa cell, did not differ between lines. In Exp. 2, cell proliferation in small follicles from the three lines was assessed after incubation of follicles in the presence of [3H]thymidine and in the presence or absence of FSH. The slope of the linear regression relating labeling index of the granulosa cells and follicle size differed significantly between High and Low lines with a significant negative coefficient for High line and a nonsignificant positive slope in the Low line. In Exp. 3, follicular fluid and serum proteins were compared between High and Low lines with 2D PAGE. A line difference was detected for a serum protein (40 kDa, pI = 6). High line had one spot, whereas Low line had three spots on 2D PAGE. This protein was not apolipoprotein E. Furthermore, the pattern of lipoproteins (high-density and low-density lipoproteins) in serum was similar between High and Low line sheep. The results indicate that selection for High ovulation rate was associated with smaller follicles that contained fewer granulosa cells per thecal cell. Aspects of function of estrogenic follicles (estradiol but not inhibin production) were also changed by selection.