Uniformity in birth weight is heritable in Norwegian White Sheep

Abstract

Birth weight is an optimum trait where very high and very low birth weights are undesirable as they may cause issues, such as dystocia, stillbirths and diminished lamb vigor. Due to economic and welfare concerns, selection for more uniform birth weight is therefore desirable at all litter sizes. If uniformity in birth weight is heritable, selection against very high and very low birth weights can be conducted. The aim of the current study was to investigate if direct and maternal genetic variances in uniformity in birth weight exist in Norwegian White Sheep (NWS). Data composed birth weights of 136,992 NWS lambs born between 2000 and 2017 and corresponding sire-maternal grand sire pedigree. The double hierarchical generalized linear mixed model (DHGLM) was fitted. The direct and maternal heritability for uniformity of birth weight were 0.08 and 0.11, respectively, and larger than for many other uniformity traits in livestock. Furthermore, the direct (57.8%) and maternal (69.4%) genetic coefficients of variation for uniformity were substantial, revealing large potential for selection for more uniform birth weight in NWS lambs. Genetic correlations between direct and maternal genetic effects on birth weight and uniformity were 0.39 and 0.12, respectively, indicating that that selection for more uniform birth weight may reduce the average birth weight genetically