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University of Wisconsin, Madison 53706
3 Address for reprint request: Department of Meat and Animal Science, University of Wisconsin, Madison 53706.
Abstract
This experiment was designed to study follicular development at various days of the estrous cycle in intact gilts for comparison with follicular growth following the removal of surface follicles from the ovaries by electrocautery at different stages of the estrous cycle. Thirty-five Yorkshire-Poland China gilts were divided equally into seven subgroups. Four of the subgroups served as controls and were slaughtered on day-2, -8, -14 or -20 of the estrous cycle (day-0 = first day of estrus), respectively, and three of the subgroups were subjected to follicle-cautery on day-2, -8 or -14 of the estrous cycle, respectively, and were slaughtered 6 days after surgery. The following cyclical variations in follicular development were found in the intact control gilts: (1) the weight of the ovarian fluid increased (P<.05) to day-8, decreased (P<.05) to day-14 and then increased (P<.05) to day-20; (2) the number of small follicles (1 to 2 mm dia.) did not differ significantly among day-2, -8 and -14, but was reduced (P<.01) at day-20; (3) the number of medium follicles (3 to 6 mm dia.) and the total number of follicles increased (P<.01) from day-2 to -8, remained approximately the same from day-8 to -14 and then decreased (P<.01) to day-20; (4) the number of large follicles (7 to 10 mm dia.) was low throughout the first three stages and then increased (P<.01) at day-20; and (5) the mean diameter of the four largest follicles increased (P<.01) from day-2 to -8, decreased slightly to day-14 and then increased (P<.01) in diameter to day-20. Results in the follicle-cautery gilts were: (1) no significant differences in the ovarian endpoints measured six days following surgery at day-2 or day-8 and (2) fewer (P<.01) small and medium follicles and total number of follicles, but more (P<.01) large follicles and a greater (P<.01) diameter of the four largest follicles at day-20 than at day-8 or day-14. Comparisons between the control and follicle-cautery gilts at the same day of the estrous cycle showed the following: (1) the control gilts had more (P<.01) ovarian fluid than the follicle-cautery gilts at day-8; (2) there were not any significant differences between the control and follicle-cautery gilts in any of the ovarian follicular endpoints at day-14; and (3) the control gilts had more ovarian fluid (P<.05), more small follicles (P<.01) and more extra-large follicles (>10 mm dia., P<.05) but fewer medium follicles (P<.01) than the follicle-cautery gilts at day-20. The particular surface follicles which have the potential to ovulate, appear to start their macroscopically-visible growth between day-8 and -14 of the estrous cycle.
1 This work was done under a cooperative agreement between the Research Division of the College of Agricultural and Life Sciences, University of Wisconsin, and the Animal Husbandry Research Division, A.R.S., U.S.D.A., and supported in part by Cooperative U.S.D.A.-C.S.R.S., Grants No. 816-15-20 and 916-15-02. It was also supported in part by the Ford Foundation, Grant No. 63-505, by the Program Project in Genetics, Grant No. GM15422, from the National Institutes of Health and by Public Health Service Training Grant No. 5-TO1 HD00104-09. This is paper no. 637 from the Department of Meat and Animal Science and No. 1721 from the Laboratory of Genetics.
2 Present address: Wisconsin Regional Primate Research Center, University of Wisconsin, Madison 53706.
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