Plasma Lh of the Prepubertal Lamb: A Possible Early Indicator of Fecundity

Genetic differences in fecundity have arisen as a result of selection for litter size in Merino sheep since 1954. The selection experiment involves three flocks designated 'O', 'T' and 'B' and their genetic history has been described by Turner (1969). In the 'O' flock, in which selection has been against multiple births, the ewes regularly have a low (0 to 10%) incidence of twin births. The 'T' and 'B' flocks have a medium (50 to 60%) and high (70 to 80%) incidence of multiple births. In the 'B' flock, about 30% of ewes have triplets and 10% have quadruplets or quintuplets each year. Current research on these groups is designed to examine the endocrine changes that have accompanied the genetic divergence in fecundity. It is known that ewes from the flocks of high fecundity