Genetic relationship between prepuberal plasma FSH levels and reproductive performance in Lacaune ewe lambs

In this study, we have estimated the phenotypic and genetic relationships between prepuberal plasma FSH level (FSH and logFSH) of ewe lambs of the Lacaune meat breed and their reproductive performance at first mating (fertility and prolificacy). Hormonal levels were assayed in a single blood sample collected at approximately 5 weeks of age (mean ± S.D. = 33.7 ± 3.2 days) from 829 ewe lambs born in July-September 1983, in 30 flocks, from 33 AI sires. Mating took place over two periods, in early breeding season at 11 months of age and in October- November at 15 months. Fertility analysis was conducted only on ewe lambs mated in June-July (n = 737), while prolificacy was analyzed for all pregnant ewe lambs (n = 732). For plasma FSH and log plasma FSH the effects of birth type, blood sampling date and time, as well as age at blood sampling were not significant (P > 0.05). The flock and sire effects were highly significant (P s 0.01) and heritability was 0.44 and 0.50 for plasma FSH and log plasma FSH respectively. The phenotypic correlation between prolificacy and FSH levels was positive but non-significant, the genetic correlation was 0.35 for plasma FSH and 0.41 for log plasma FSH. Prepuberal FSH levels of ewe lambs which remained barren after their first mating early in the breeding season were significantly higher than that of pregnant ones (P ! 0.05). Nevertheless the genetic correlation between fertility and logFSH was significantly positive (P:s 0.05).