Dutch Friesian heifers (n = 13) and cows (n = 13) were used to obtain information about the number, size and micromorphology of antral follicles (≥ 3 mm in diameter) in cattle after induction of luteolysis with the PGF_2α analogue luprostiol. Special attention was paid to the presence of atypical granulosa cells in these follicles to obtain additional data to help evaluate the hypothesis that these cells are markers of follicular atresia. Animals were injected i.m. with 15 mg of the synthetic prostaglandin on day 10 or day 11 of the oestrous cycle. The ovaries were collected on day 12, that is 48 and 24 h after injection of luprostiol, respectively. After prostaglandin-induced luteolysis, the mean number of medium-sized and large nonatretic follicles and of medium-sized atretic follicles had not changed in heifers and in cows, compared with those of untreated animals. However, in heifers, contrary to cows, the development of a preovulatory-sized follicle was initially accompanied by an increase in the number of large definitely atretic follicles. Atypical granulosa cells can be considered as markers for a lower quality follicle, on the basis of their absence in preovulatory-sized follicles and their presence in large numbers in a high proportion of definitely atretic follicles. If it is assumed that only a nonatretic follicle without atypical granulosa cells will grow to preovulatory size, growth of this follicle within 2 days after prostaglandin treatment was almost 9 mm and over 10 mm in heifers and cows, respectively. In cows, most growth of follicles was observed at the first day after prostaglandin treatment; in heifers, this occurred one day later.

Summary. Five Dutch–Friesian heifers were injected i.m. with 3000 iu pregnant mares' serum gonadotrophin (PMSG) on day 10 of the oestrous cycle, to study the effects on the number and micromorphological quality of antral follicles (⩾0·3 mm in diameter). The ovaries were collected 48 h after PMSG injection.

As well as the presence of mitotic figures and the absence of pyknotic nuclei in the granulosa, atypical granulosa cells were found in nonatretic follicles. These cells had an oblong nucleus and stained with toluidine blue. They were characterized by their dark cell matrix, and the presence of numerous free ribosomes and intermediate filaments of varying quantity. Atypical granulosa cells were micromorphologically similar to fibroblast-like cells in the theca. Their presence coincided with the occurrence of degenerative changes in the cytoplasm of nearby granulosa cells and they were more frequent in atretic follicles. The presence of atypical granulosa cells in follicles hitherto called nonatretic is therefore probably associated with the onset of follicular atresia.

In the PMSG-treated heifers, the mean number of large (⩾6·0 mm in diameter) antral follicles was greater than in the control group (18·4 ± 4·0 versus 3·0 ± 1·0), because of an increase in the number of large nonatretic follicles (11·8 ± 4·4 versus 0·4 ± 0·2). After hormone treatment, the mean number of medium-sized (3·0–5·9 mm) nonatretic follicles also increased (6·4 ± 1·3 versus 1·8 ± 1·0). PMSG did not change the mean number of nonatretic follicles < 3·0 mm or that of atretic follicles in the different size categories. However, when follicles hitherto called nonatretic, with atypical granulosa cells, were taken together with the group of atretic follicles, PMSG appeared to increase the mean number of large atretic follicles (13·6 ± 2·4 versus 3·0 ± 1·0). The mean number of medium-sized and large nonatretic follicles without atypical granulosa cells was markedly increased (3·8 ± 1·0 versus 0·2 ± 0·2 and 4·6 ± 1·9 versus 0·0, respectively). The data demonstrate that PMSG stimulates the formation not only of nonatretic follicles ⩾3·0 mm, but also of atretic follicles ⩾6·0 mm.

Keywords: ovary; follicle; micromorphology; pregnant mares' serum gonadotrophin; heifer

Summary. Serum testosterone concentrations ranged from 0·24 to 1·45 nmol/1 between Day 53 post coitum (p.c.) until Day 40 post partum (p.p.) and did not show variations that could be correlated with the process of testicular descent. The intratesticular androgen appeared to be mainly testosterone, its concentration being about 5000-fold higher than that in serum whereas 5α-dihydrotestosterone could not be demonstrated. The intratesticular testosterone concentration at the initiation of gubernacular regression (Day 0) was apparently, but not significantly, higher than at Day 49 p.c. and at Day 40 p.p. The ability of the neonatal canine testis to synthesize testosterone was indicated by increased serum testosterone concentrations after hCG stimulation.