Abstract:
Concentrations of FSH were measured in new-born lambs in Booroola Merino x Romney and Booroola Merino flocks where the Booroola F gene was segregating, and in progeny from sires of a prolific strain of Romney sheep. FSH concentrations increased with age and liveweight in Booroola Merino x Romney ewe lambs to reach peak concentrations at 4-6 weeks of age. Significantly higher mean concentrations were recorded in ewe lambs homozygous for the Booroola gene (FF) compared with non-carrier (+ +) ewe lambs. Concentrations in heterozygous (F+) ewe lambs were intermediate. Maximum differences between the genotypes were recorded at 6 weeks of age. Significantly higher FSH concentrations were also recorded in F-gene-carrier female lambs when compared to non-carriers in two other flocks. FSH concentrations remained low in ram lambs up to 12 weeks of age, and there were no differences between Booroola genotypes. The progeny of one ram from the prolific Romney family had high ovulation rates at 18 months of age. The progeny of other related rams showed no increase in ovulation rates at 18 months of age. Concentrations of FSH in the high-ovulation-rate progeny at 3 and 5 weeks of age did not differ from those in the low-ovulation-rate progeny, but were lower than those in the progeny of an FF Booroola Merino x Romney ram. These results support the hypothesis that neonatal concentrations of FSH are higher in lambs carrying the Booroola F gene, but not in all prolific strains since high FSH concentrations were not recorded in daughters from a prolific Romney flock.(ABSTRACT TRUNCATED AT 250 WORDS)