Primordial Follicle Numbers in Ovaries and Levels of LH and FSH in Pituitaries and Plasma of Lambs Selected for and against Multiple Births

Abstract

The numbers of primordial follicles in ovaries of ewe lambs, from two groups of Peppin Merinos that had been selected for (T group) and against (0 group) mUltiple births, were estimated at birth, 7 days and 5 months of age. Peripheral plasma and anterior pituitary levels of LH and FSH were determined by radioimmunoassay in the lambs at 5 months of age. These lambs were either entire or unilaterally ovariectomized (hemispayed) at 7 days of age.There was no difference in primordial follicle numbers between lambs at birth and 7 days of age, but when paired ovaries of hemispayed lambs at 7 days and 5 months of age were compared there was a significant increase in follicle numbers with age (34903 v. 48047). O-group lambs had more primordial follicles than T-group lambs at birth and 7 days of age (65501 v. 37797) and there was a similar but not significant difference at 5 months of age (53934 v. 44057).Peripheral plasma LH was higher in T-group than in O-group lambs and plasma LH levels were correlated to pituitary LH content (r = o· 75). Vesicular follicles larger than 2 mm in diameter were present only in ovaries of lambs with plasma LH levels above 3· 0 ng/m!. Pituitary FSH levels were considerably higher in hemispayed lambs than in entire lambs and there was a trend to higher levels in T-group lambs when compared with O-group lambs.It is concluded that genetic selection for the incidence of multiple births has resulted in changes in the number of ovarian primordial follicles of the post-natal lamb and it is suggested that these changes may be related to the levels of pituitary gonadotrophins.

Developmental Expression and Distribution of N- and E-Cadherin in the Rat Ovary1

“…Although primordial follicle formation and the initiation of follicle development occurs in the ovary of many mammals during fetal development [33][34][35] (except for the rodent where these occur in the immediate postpartum period) [17], subsequent folliculogenesis extends throughout the reproductive life of the female. Considerable progress has been made in our understanding of the regulation of physiological and molecular events involved in follicle maturation and ovulation [36,37].…”

Ovarian Follicles of New-born Merino Lambs from Genetic Lines which Differ in Fecundity

“…In order to make realistic comparisons between genotypes, adjustment must therefore be made for differences in the distribution of birth types. In the earlier study of Trounson et al (1974), in which data were not corrected for litter size at birth, the numbers of primordial follicles were significantly different in lambs from T and 0 flocks. Mter adjustment for litter size ,and sire in the present experiment the T and 0 were not significantly different.…”

“…Tassell et al Follicles were classified as described by Trounson et al (1974) and Tassell et al (1978). Primordial, small and large growing (non-vesicular), and partially and fully formed vesicular follicles were counted.…”

“…Their genetic history and flock performances have been described by Turner (1978). Trounson et al (1974) reported that lambs from the 0 flock had more ovarian primordial follicles than lambs from the T flock and concluded that genetic selection for the incidence of multiple births has resulted in changes in the number of primordial follicles of the post-natal lamb. This study was designed to determine if this conclusion was substantiated from examination of ovaries from Booroola lambs and additional lambs from the T and 0 flocks.…”

Ovarian follicular growth during the oestrous cycle in two breeds of ewes of different ovulation rate, the D'Man and the Timahdite

“…The first studies on the relationship between the populations of primordial follicles and ovulation rate examined the relation between the number of germinal cells present in the ovary at birth in females from a given genetic line and the mean ovulation rate of that line (sheep: Land, 1970;Trounson, Chamley, Kennedy & Tassell, 1974;Cahill, Mariana & Mauléon, 1979;mouse: Iones & Krohn, 1961 ; rat: Land, de Reviers, Thompson & Mauléon, 1974). These authors all showed that there is a negative correlation between the number of primordial follicles and ovulation rate.…”