The Relation between Patterns of Ovarian Follicle Growth and Ovulation Rate in Sheep

Abstract

The number and growth rate of follicles within classes based on granulosa volume were determined for ovaries taken from groups of 4-5-year-old,. fine-wool Merino ewes drawn at different times of the year from a single strain flock maintained at Armidale, N.S.W:The breeding season of the flock normally extends from February to October and the mean ovulation rate rises from about 0·5 in February to about 1·8~1·9 during April-May.Ewes sampled when they were anoestrous or had one (single-ovulatory) or two (twin-ovulatory) recent corpora lutea did not differ in respect to the mean total number of ovarian follicles.ithe mean number of follicles in individual classes, the time for follicles to complete their rapid growth stage, or the incidence of follicle atresia. However, the ovaries of twin-ovulatory ewes contained signifi. . . cantly more follicles in the two terminal classes within the rapid growth stage thandid the ovaries of single-ovulatory or anoestrous ewes (2·2 v. 0·9 and 1·0). This difference was attributed to. the differing numbers of follicles per day entering into the rapid growth stage (5 ·2, 4· 5.and .3·7 respectively in twin-ovulatory, single-ovulatory and anoestrous ewes).'

Seasonal effects on ovarian follicular development in pony mares

“…This is further supported by data involving light treatments (Kooistra and Ginther, 1975) (Driancourt, Mariana and Palmer, 19821. In contrast, the close values among the three groups of the mitotic index of antral follicles were expected since a similar fact has been demonstrated in ewes (Turnbull et al, 1978 ;Cahill and Maul6on, 1980 …”

“…Thus, as in ewes (Turnbull et al, 1978 ;Cahill and Mauleon, 1980), the only part of folliculogenesis lacking during winter is preovulatory development. Furthermore, anestrous follicles seem to be sensitive to endogenous or exogenous hormones since Oxender, Noden and Hafs (1977) have noticed some spikes of estradiol-17(3, and ovulation has been successfully induced with pituitary extracts in a fortnight in seasonally anovulatory mares (Douglas, Nuti and Ginther, 1974 ;Lapin and Ginther, 1977).…”

Follicular kinetics in the mare ovary

“…Using the latter model, we found that the follicular population and the ovarian status are not strongly depressed. As in the ewe, preovulatory follicles are lacking (Cahill, 1979b ;Turnbull et al, 1979), and the size of the largest follicle is highly variable (Sharp, 1975). With the exception of data from Freedman, Garcia and Ginther (1977) (Peters et al, 1975) or ewes either in vivo (Turnbull et al, 1977) (Lushbauch, 1956 ;Mazia, 1961 ;Turnbull et al, 1977 ;Cahill, 1979 mostly lie between these.…”

Factors regulating ovulation rate in the ewe

“…Extensive morphological studies of follicle populations in sheep with genetically determined differences in ovulation rate have been reported (Turnbull, Braden & Mattner, 1977;Turnbull, Mattner, George & Scaramuzzi, 1978;Cahill, Mariana & Mauléon, 1979;Cahill, 1981). The distribution of follicle populations in Romanov sheep shows them to have increased numbers of antral follicles and decreased numbers of primordial follicles.…”