Study of LH response to GnRH in the young male as a criterion of genetic merit for female reproduction in sheep

Abstract

Summary. A high and a low response line in sheep were selected on the basis of the mean concentration of LH in 10-week-old Finn\p=n-\Dorsetram lambs after an i.v. injection of 5 \g=m\g GnRH. After 8 male generations the mean LH response of the high line was more than 5-fold that of the low line and the heritability of the selected trait was estimated at 0\m=.\44 \m=+-\0\m=.\015. Highly significant line differences in mean LH response to GnRH were also found in males at 20 weeks of age and females at 10 and 20 weeks of age and the genetic correlations between the four LH response traits appear to be close to unity. Large line differences in the mean FSH response to GnRH were also found in both males and females at 10 and 20 weeks of age. Selection had little effect on the physical characteristics of lambs. High-response line ewes entering their first breeding season at about 7 months of age showed oestrus earlier in the season and had higher ovulation rates and numbers of lambs born per ewe lambing than did low-response line ewes. In the second breeding season, at about 19 months of age, the only line difference was a higher ovulation rate early in the breeding season in high-line ewes. It is suggested that these changes may be mediated by a more rapid response in high-line ewes to increased GnRH stimulation at puberty or at the beginning of the breeding season.

Two-trait random regression model to estimate the genetic association of scrotal circumference with female reproductive performance in Nelore cattle

“…Land [1] pointed out that the gonads in males and females are stimulated by FSH and LH; thus, the correlations between male and female traits are justifiable. Haley et al [31] reported that essentially the same genes are responsible for the LH response to GnRH at 10 and 20 weeks of age and in male and female sheep. Haley et al [31] also stated that these same genes appear to be involved in the production of FSH.…”

“…Haley et al [31] reported that essentially the same genes are responsible for the LH response to GnRH at 10 and 20 weeks of age and in male and female sheep. Haley et al [31] also stated that these same genes appear to be involved in the production of FSH. Lunstra [32] found that the levels of LH and the SC were significantly increased with advancing age in young bulls of different breeds.…”

Development of the endocrine reproductive axis in hair breed ram lambs

“…between individuals, however, might be of some value to predict the reproductive performance of the ram in the adult life or its progeny (27,35) , but such possibility cannot be verified from data of the present study.…”

“…Es posible que en condiciones fisiológicas, el hipotálamo genere sólo los estímulos necesarios para desencadenar los cambios endocrinos asociados con el inicio de la pubertad y el desarrollo sexual, por lo cual, los perfiles de LH y T no difirieron entre genotipos (27) . La respuesta diferenciada a la administración de GnRH entre genotipos o entre individuos, sin embargo, podría ser de algún valor para predecir el comportamiento reproductivo del animal en la vida adulta o de su progenie (27,35) , pero tal posibilidad no puede ser verificada a partir de los datos del presente estudio.…”

Extra- and Intracellular Effects of Divergent Selection for Pituitary Responsiveness to Gonadotropin-Releasing Hormone in Prepubertal Ram Lambs1

“…Details of the selection criteria and the correlated responses in reproductive performance have been reported previously [1,2]. Physiological studies of both prepubertal lambs (male and female) and adult ewes from these lines, referred to as low and high lines, have demonstrated that the two lines differ significantly in their ability to release LH in response to both pharmacological [3][4][5] and physiological [5] doses of exogenous GnRH. Between-line differences in LH pulse amplitude have also been identified in both prepubertal males [6] and adult females [7], despite the absence of direct selection for these characteristics.…”