Lifetime Reproductive Performance of Booroola Merino X Romney Ewes of Differing Genotype for the Booroola Fecundity Gene and Romney Ewes

First cross Booroola Merino x Romney (B x R) ewes born in 1975, 1976, 1978 and 1979 were classified as being heterozygous (F+) or non carriers (++) for the Booroola fecundity gene. Their performance as hoggets (< 1 year of age) I and to six years of age (1975 and 1976 bornonly) was compared with contemporary Romney (R) ewes. As hoggets, the F+ ewes had ovulation rates about 0.5 higher than ++ B x R and R ewes. As adults B x R ewes were 5-7 kg lighter at joining than R ewes. Mean ovulation rates were 0.06-0.16 and 1.28-1.55 higher for ++ and F+ B x R ewes respectively than R ewes which together with differences in barrenness and lamb survival gave 0.05-0.32 and 0.35-0.85 more lambs tailed per ewe joined.