Genetic segregation for fecundity in booroola merino sheep

Abstract

The CSIRO Booroola Merino flock began with a sample of 14 ewes and 2 rams from a commercial flock selected on the ewe side only for increased multiple births. Analyses of the lifetime lambing records of the foundation ewes and of their daughters sired by foundation rams, indicate the existence of a major gene affecting fecundity in the Booroola Merino. Heterozygous carriers of the postulated gene, identified as having 1 or more litter size records ≥ 3 during their lifetime, have a mean litter size 2 to 3 standard deviations (one lamb per lambing) higher than non-carriers. The mode of action of the postulated gene appears to be addictive for ovulation rate, but may be almost completely dominant in terms of litter size.