Ovarian follicular development during early pregnancy in cattle

Publisher Website
Google Scholar
Abstract
On the day of oestrus (Day 0), 23 cows were assigned randomly to 4 groups in a 2 .times. 2 factorial experiment. Main effects were cow status [pregnant (P) versus non-pregnant (NP; not mated)] and day (Day 17 versus Day 34) when cows were slaughtered and ovaries collected; i.e. Groups NP-17 (N = 6), NP-34 (N = 5), P-17 (N = 6) and P-34 (N = 6). To mimic CL maintenance associated with presence of a conceptus in Group P-34, cows assigned to Group NP-34 were hysterectomized between Days 4 and 6 after oestrus. Pregnancy in Groups P-17 and P-34 (recovery of conceptus) and CL maintenance between day of surgery and Day 34 in Group NP-34 were confirmed. In Group NP-17, all cows except one were slaughtered before luteolysis. CL-bearing ovaries were serially sectioned (10 .mu.m) and follicles (> 0.15 mm) were counted and measured using routine histological techniques. For each size class of follicles, the percentages of follicles were similar (P > 0.1) on Days 17 and 34. The percentage of non-atretic follicles (< 4 pycnotic bodies) was lower (P < 0.002) in pregnant than non-pregnant groups in the smallest class of antral follicles (0.16-0.28 mm) but was higher (P < 0.03) in larger classes (0.68-3.67 mm) for pregnant groups. Percentages of atretic follicles were 3.7 and 4.9 (P > 0.1) for follicles of 0.16-0.67 mm, 91.1 and 78.9 for follicles of 0.68-3.67 mm (P < 0.04) and 5.1 and 16.1 (P < 0.05) for follicles of 3.67-78.56 mm in pregnant and non-pregnant groups, respectively. The percentage of atretic follicles classified as late atretic was higher in pregnant than in non-pregnant groups for follicles of 0.68-1.57 mm (P < 0.06) and 3.68-8.56 mm (P < 0.05). The results suggest that, as early as Day 17, the presence of a conceptus favours a more rapid turnover of follicles from class 1 (0.16-0.28 mm) to classes 3 and 4 (0.68-3.67 mm) but limits further growth by increasing atresia.