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Summary. Ovaries were obtained at slaughter from 12 Holstein dairy cows at 15, 25 or 35 days after their 4th calving. Non-atretic and atretic antral follicles were separated into 6 size classes according to size and the numbers in each class were expressed as a percentage of the total for each ovary. Non-atretic follicles of diameter 0·1 6–0·28 mm decreased from 27·5% at Day 15 to 1·5% at Day 35 whereas those of 0·29–0·67 mm and 0·68–1·57 mm diameter increased from 37·4 to 47·2% and from 11·5 to 17·3% respectively (all P < 0·05). The proportions of follicles measuring 1·58–3·68, 3·69–8·56 and > 8·56 mm remained almost constant. The atretic follicles of 0·29–3·68 mm varied significantly in number according to the post-partum interval and to whether they were in the ovary containing the CL of pregnancy. It is concluded that the CL of pregnancy and/or the conceptus have a carry-over effect on the rate of growth of the antral follicles even after parturition.

Summary. In ewes at the 1st, 2nd or 4th oestrous cycle after unilateral ovariectomy, the ovulation rate remained constant at 1·5 in the control (sham-operated) ewes, but increased from 1·3 to 2·0 in unilaterally ovariectomized ewes.

In control ewes, the proportion of preantral follicles declined significantly (P < 0·05) with each oestrous cycle while the antral follicles increased as the breeding season progressed (P < 0·05). In contrast, after unilateral ovariectomy, the proportion of preantral and antral follicles remained constant throughout the cycles studied. The rate of atresia of antral follicles, especially those from small size classes, decreased significantly after one cycle of unilateral ovariectomy (P < 0·05). Larger antral follicles had a different rate of atresia as the breeding season advanced. It is concluded that unilateral ovariectomy acutely decreased the rate of atresia and maintained the within-ovary equilibrium between preantral and antral follicles which otherwise would have decreased due to the depletion of preantral follicles with the advance of the breeding season.

Histochemical methods have been widely used for the detection and localization of hydroxysteroid dehydrogenase activity, mainly in steroid-hormone producing organs and tissues (Baillie, Ferguson & Hart, 1966). Hay & Deane (1966) attempted to demonstrate Δ⁵-3 β- and 17 β-hydroxysteroid dehydrogenases in testicular tissue of the larger farm animals. In the adult boar, an intense staining reaction in the interstitial tissue of the testes, incubated without substrate added to the medium, prevented the histochemical demonstration of a specific reaction for Δ⁵-3 β-hydroxysteroid dehydrogenase. In view of the high production of both oestrogens and androgens by the adult males of this species (Raeside, 1965), it seemed of particular interest to be able to apply methods for the detection of hydroxysteroid dehydrogenase activity to testicular tissue of the adult boar.

Testes were obtained from two adult boars

Summary. Follicular growth rates were studied in 5 Hereford-Holstein cross heifers on Day 14 of the oestrous cycle. The granulosa cell mitotic index (MI) was measured in non-atretic antral follicles of various diameters (0·13–8·57 mm) from Bouin-fixed ovaries collected before (199, control) and 2 h after colchicine treatment (189, treated). In control ovaries, follicles of 0·68–1·52 mm had a higher MI than those of other size classes (P < 0·05). In colchicine-treated ovaries, the MI of follicles ranging from 0·68 to 8·57 mm increased more than that of other sized follicles, so that the mitotic time was shorter (0·78 h vs 1·32 h) in medium and large sized follicles (0·68–8·57 mm) than in smaller follicles (0·13–0·67 mm). Calculations based on the number of granulosa cells in follicles of various classes and from the time required to double the number of cells within a follicle indicate that a follicle takes 27 days to grow from 0·13 to 0·67 mm, 6·8 days from 0·68 to 3·67 mm and 7·8 days from 3·68 to 8·56 mm, indicating that growth rates varied with the size of the follicle. A period equivalent to 2 oestrous cycles would therefore be required for a follicle to grow through the antral phase, i.e. from 0·13 mm to preovulatory size. Increased MI, decreased mitotic time and increased atresia found in follicles larger than 0·68 mm could indicate a change in the follicular metabolism during its maturation.

Summary. The effects of hypophysectomy and unilateral ovariectomy on the total number of follicles with >3 layers of granulosa cells were determined at 4 and 70 days following treatment.

The population of preantral follicles (<0·23 mm diam.) was found to be under the control of gonadotrophins but such control was only evident on a long-term basis. At 70 days after unilateral ovariectomy there was a large increase in the number of preantral follicles but at 70 days after hypophysectomy there was a large decrease.

The population of antral follicles (>0·23 mm diam.) was under the immediate control of gonadotrophins. By 4 days after hypophysectomy all large antral follicles had become atretic and the number of antral follicles was further decreased at 70 days after treatment. At 70 days after unilateral ovariectomy there was an increase in the number of antral follicles.

The follicular growth rates at 70 days following treatment were decreased in hypophysectomized ewes but increased in ewes after unilateral ovariectomy.

Summary. To study the influence of the F gene on follicular dynamics and dominance, 2-year-old Booroola × Finnish Landrace (BFL, N = 17) and Booroola × Suffolk (BS, N = 18) ewes were compared with contemporary purebred Finn (FL, N = 18) and Suffolk (S, N = 18) ewes. In Exp. 1, oestrous cycles of ewes were synchronized during the breeding season with progestagen-impregnated sponges. At sponge removal (Day 0), 14 days after insertion, ewes of each of the 4 genetic groups were assigned to Group 1 in which all follicles visible on both ovaries were destroyed by electrocauterization except for the largest (F1) which was marked, Group 2 in which all visible follicles on both ovaries were destroyed, or Group 3 in which the 3 largest follicles of both ovaries were identified as F1, F2 and F3 and marked. At 48 h after treatment (Day 2), follicular growth was evaluated. At Day 0, the mean number of small follicles (1–3 mm) was higher (P < 0·05) for BS, S and BFL (35·8, 35·1 and 32·9) than FL (24·9) ewes. Large follicles (≥4 mm) were more numerous (P < 0·05) in FL (3·5) than in BS (2·1) ewes, BFL and S ewes being intermediate. Diameter of the F1 follicle was larger (P < 0·05) for S (7·6 mm) than FL, BS and BFL (5·8, 5·1 and 5·1 mm) ewes. In Group 1, all F1 follicles marked at Day 0 ovulated at oestrus after sponge removal for BFL, BS and S ewes while in FL ewes, 2 of 6 F1 follicles regressed. In ewes ovulating, only the Fl follicle ovulated except for one S ewe which shed one more ovum. In Group 2, there were no follicles ≥4 mm at Day 2 and no ewes ovulated after treatment. In Group 3, the proportion of marked follicles that ovulated was higher for S ewes than in those of the prolific genotypes. The number of follicles not marked at Day 0 but ovulating (compared to the total number of ovulations) was higher in BFL, BS and FL (8/11, 9/13 and 9/13) than S (3/10) ewes. In Exp. 2, prolific (BFL + BS) and non-prolific (S) ewes were compared following destruction of follicles ≥3 mm with the F1 left intact (Treatment 1) or destroyed (Treatment 2), 12 days after sponge insertion. At 4 days after treatment (at sponge removal), the numbers of 3–4 mm follicles were not different between the 2 treatments and a very high proportion of the F1 follicles left intact at Day 0 had regressed at Day 4 in both genotypes. From these results, it can be concluded that the higher ovulation rate in Booroola-crossed ewes is not associated with a higher number of recruitable follicles but involves late follicular-phase recruitment and selection combined with smaller preovulatory follicle diameters. Dominance by the largest follicle is not present in ewes of prolific or non-prolific genotypes. In contrast, it is likely that small sized follicles exert a negative effect on growth of large follicles.

Keywords: ewes; Booroola; atresia; follicle; dominance

Summary. On the day of oestrus (Day 0), 23 cows were assigned randomly to 4 groups in a 2 × 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 μm) 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.