Morphological and functional characterization of large antral follicles in three breeds of sheep with different ovulation rates.

Morphological and functional features of large ovarian follicles from three breeds of sheep, with different ovulation rates (Finnish Landrace N = 12, Finnish Landrace X Scottish Blackface N = 16, Merino X Scottish Blackface N = 16) were compared by integrating three techniques; ink labelling, in-vitro oestradiol production and morphological classification. The follicles were removed at two stages of the follicular phase, 1 (PG + 1) or 2 (PG + 2) days after PGF-2 alpha treatment and compared after monitoring their rates of growth with the use of ink labelling. After ovariectomy all follicles greater than or equal to 1 mm in diameter were dissected, and the 8 largest were incubated individually for 2 h to assess their ability to secrete oestradiol and testosterone. After incubation the follicles were processed for histological examination and checked for atresia. An analysis of the follicle population was based on in-vitro oestradiol secretion rates in all three breeds; an oestrogen-active population producing 500-8100 pg oestradiol/ml/h and an oestrogen-inactive population producing 0-499 pg oestradiol/ml/h. A comparison of the 3 approaches demonstrated agreement on 94.3 +/- 1.2% of occasions. Ink-labelling demonstrated that all follicles identified as oestrogen-active were increasing in size. Within oestrogen-active follicles significant correlations were detected between oestradiol production and testosterone production (r = 0.42), oestradiol production and granulosa cell number (r = 0.45) and between oestradiol production and mitotic index (r = -0.38). A regression model fitting breed, stage of atresia, granulosa cell number, in-vitro testosterone production and mitotic index demonstrated that granulosa cell number is a characteristic which contributes significantly to the variation of in-vitro oestradiol production in oestrogen-active and oestrogen-inactive follicles. There was no significant difference between breeds in the mean number of ink-labelled follicles growing from Day PG - 1 to Day PG + 1. There was a significant difference between the breeds in the number of ink-labelled follicles growing between Days PG + 1 and PG + 2 (Days 1 and 2 of the follicular phase), the number being similar to the ovulation rate for the breed. The majority of the oestrogen-active follicles had been recruited by Day PG - 1, although in the Finnish Landrace genotypes more than 30% were recruited on or after Day PG + 1 compared to less than 10% in Merino x Scottish Blackface ewes.(ABSTRACT TRUNCATED AT 400 WORDS)

Variations in patterns of follicle development in prolific breeds of sheep.

Prolific breeds of sheep (Romanov, Finn and Booroola Romanov crosses heterozygous for the Booroola gene (F+) were compared with breeds of lower prolificacy (Ile-de-France, Finn X Scottish Blackface, Merino X Blackface and Booroola X Romanov not carrying a copy of Booroola gene (++] by in-vivo monitoring of follicular kinetics by ink labelling during the late luteal phase and follicular phase of the oestrous cycle followed by histological examination of the ovaries or follicle dissection. At each of 3 successive laparotomies, the 3 largest follicles of each ovary were measured and ink labelled. At the final laparotomy, around the beginning of oestrus, all ewes were ovariectomized. High ovulation rate was not associated with the total number of antral follicles in any of the breeds. However, there were more follicles greater than 2 mm in diameter in Romanov and Booroola X Romanov crosses (F+) compared to their respective controls. Such a feature was not observed in Finnish Landrace compared to Finn X Blackface and Merino X Blackface ewes. A more numerous population of recruitable follicles, together with a similar incidence of selection through atresia, were the features associated with the high ovulation rate of Romanov compared to Ile-de-France ewes. The high ovulatory potential of the Finn ewes resulted from a markedly reduced incidence of selection through atresia. Booroola X Romanov ewes carrying a copy of the Booroola gene (F+) appeared to possess features of both parental breeds, including high numbers of recruitable follicles, smaller follicular size when recruitment occurs and an extended time for recruitment. Booroola X Romanov (++) ewes, not carrying the gene, appeared to have lost part of the 'Romanov characteristics' of a more numerous population of recruitable follicles. The variability in the kinetics of preovulatory enlargement, seen in these breeds of sheep, demonstrates that there are a number of pathways through which high ovulation rate can be achieved and hence through which ovulation rate might be manipulated.

Fertility of sheep given antisera to steroids during anoestrus.

The incidence of oestrus (6/46) and ovulation (14/46) in ewes given antisera to androstenedione, oestrone, oestradiol and testosterone either separately or as a mixture of these sera at the time of treatment with progestagen sponges alone or progestagen sponges followed by LH-RH was similar to that of control ewes (2/13 and 6/13 respectively). The number of corpora lutea (CL) recorded for those ewes that did ovulate was, however, greater in the antiserum-treated ewes (22 CL/14 ewes) than in the controls (6 CL/6 ewes) at the first ovulation after sponge withdrawal. This superiority persisted to the second ovulation (53 CL/42 treated ewes compared to 13 CL/13 controls). The results for groups treated with antisera did not differ amongst themselves.