Plasma LH, FSH and testosterone concentrations in adult rams which were homozygous carriers or non-carriers of the Booroola fecundity gene

Abstract

No gene-specific differences were found with respect to LH or testosterone pulsatile secretion (over 12 h), or in 12 hourly mean FSH concentrations in adult Booroola FF and ++ rams. Also, no differences between genotypes in the LH response to an injection of testosterone propionate, the FSH response to an infusion of bovine follicular fluid, or the testosterone response to injections of PMSG were noted. However, during the phase of seasonal testicular development, mean testosterone pulse amplitude (over 12 h) and the FSH response to 25 μg GnRH were higher in FF than in ++ rams (P < 0.05); there were also significant effects of sire (P <0.05 in FF genotype only) and litter size (P < 0.05) on testosterone pulse amplitude and GnRH-stimulated FSH release, respectively. During the breeding season, mean LH, but not FSH, concentrations were higher in FF than in ++ rams, after an injection of 0.5 μg GnRH; LH release was not affected by sire or litter size (P > 0.05). Long-term studies revealed that the FF rams were born in significantly larger litters, they weighed significantly less than ++ rams (P < 0.05), and that bodyweight was significantly correlated (P < 0.05) with litter size. There were no differences in testis size, and testis size was not significantly correlated with bodyweight. There was a strong tendency (P = 0.056) for overall mean FSH concentrations, measured weekly for 9 months, to be highest more often in FF than in ++ rams. Collectively, these results suggest that the F gene is expressed at the level of the pituitary gland in adult males, although in intact animals gene-specific differences are suppressed by the negative effect of hormones from the testis.