Genetic opportunities to improve lamb weaning rates in Merinos

Abstract

Opportunities to improve genetic merit for number of lambs weaned (NLW) and scrotal circumference (SC) are relatively untapped by Merino breeders. Data from the Merino Genetic Services (MGS) database was analysed to determine the heritability of yearling and hogget scrotal circumference and number of lambs weaned as well as their genetic correlations. NLW was found to be lowly heritable at 0.06. Scrotal circumference at yearling and hogget ages was moderately heritable at 0.37 and 0.36 respectively. The genetic correlation between yearling SC and NLW was moderately positive at 0.35 (0.30) suggesting that yearling SC may be a useful indirect selection tool for NLW. The standard error associated with these correlations suggests that more data is needed to more accurately describe this relationship. Examination of the range in estimated breeding values (EBV) within the MGS database illustrates significant genetic variation for these traits. Among the 256,000 Merinos in this database the range in NLW EBV is 77.3%. That is, the daughters of a ram at the high end of the range are expected to wean, on average, 38.6% more lambs than the daughters a ram at the low end of the EBV range. The range in yearling scrotal circumference EBV is 6.3cm. Given the estimated genetic variation in NLW and SC and the genetic parameters derived from this data set there appear to be significant genetic opportunities for improved lamb weaning rates in Merino sheep.