Genetic parameters for early lamb survival and growth in Scottish Blackface sheep

The objectives of this study were 1) to estimate the heritability of lamb survival and growth in the Scottish Blackface breed; 2) to examine the relationship between lamb survival and live BW; and 3) to investigate the possibility of using lamb survival in a breeding program for this breed. The data used for the analyses contained information about survival and live BW at different ages on 4,459 animals. The records were collected from 1988 to 2003 in a Scottish Blackface flock. Live BW was recorded every 4 wk from birth to 24 wk. Survival was defined either by perinatal or postnatal mortality (up to weaning at 12 wk), or as cumulative survival to 1, 4, 8, and 12 wk. The pedigree file comprised 1,416 dams and 178 sires. A sire model was used to estimate genetic parameters for binary survival traits. Heritabilities of BW traits, and phenotypic and genetic correlations between BW and between survival and BW were estimated by fitting an animal model. Further, correlations of survival with live BW were estimated by using a Markov chain Monte Carlo threshold model, implemented by Gibbs sampling. The heritability estimates for cumulative lamb survival declined from birth onward (from 0.33 to 0.08), and postnatal survival had a heritability of 0.01. The direct and maternal heritabilities for BW traits ranged from 0.08 to 0.26 and from 0.06 to 0.21, respectively, whereas the maternal environmental component was between 0.04 and 0.16. The genetic correlations between BW traits at different ages were high. The genetic and phenotypic correlations between survival and BW were always positive (ranging from 0.04 to 0.54), so there was no antagonism between these traits. Therefore, it is possible to simultaneously improve both survival and live BW in a breeding program for this breed. Key words: binary trait, genetic parameter, lamb survival, live weight