Ovarian follicular growth during the oestrous cycle in two breeds of ewes of different ovulation rate, the D'Man and the Timahdite

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Abstract
The population of growing follicles of diameter > 60 .mu.m was studied in 24 D''Man and 24 Timahdite ewes aged 2-2.5 yr. The ovaries of each ewe were removed on Days 1, 2, 3, 4, 5, 7, 9, 11, 13, 15 or 17 of the estrous cycle. Two ewes from each breed were ovariectomized. The mean ovulation rate was 2.9 in D''Man and 1.1 in Timahdite ewes and the mean numbers of normal follicles were 276 and 230, respectively. The distribution of the various sizes of follicles did not differ significantly between the 2 breeds. However, the number of follicles of diameter 118-462 .mu.m (follicles beginning to develop an antrum) and the number of follicles of diameter > 1285 .mu.m (large follicles possessing an antrum) were significantly greater in the D''Man than in the Timahdite ewes (136 and 106, and 7.1 and 4.5, respectively). The mean number of atretic follicles was similar for the 2 breeds (13.3 in the D''Man; 12.2 in the Timahdite), but in the D''Man there was a lower rate of atresia (54.9 compared with 66.7%) for follicles of 1084-2141 .mu.m diameter. During the 1st days of the cycle there was a significant decrease in both breeds in the number of follicles of 60-118 .mu.m diameter. During this same period there was a significant decline in the number of follicles of diameter 119-462 .mu.m but in the D''Man ewes only. The higher ovulation rate of the D''Man breed apparently is due to the greater number of those follicles from which ovulatory follicles are recruited.

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