Genetic analysis of a maternal assistance score in sheep

Abstract

Maternal behaviour is important for lamb survival, as ewes perform many behaviours that affect the chances of a lamb surviving. Collecting maternal behaviour data directly at lambing is time-consuming and not considered suitable for acquiring the large volumes of data that would be required for using as selection criteria within commercial breeding flocks. The aim of this study was to investigate if a simple scoring system is heritable and assesses the expression of behaviours that reduce the probability of lamb mortality. Ewe behaviour was scored on a 3-point Maternal Assistance Score (MAS): (1) the ewe shows a high level of maternal interest (assumed if no intervention required); (2) the ewe shows limited interest in her lamb; and (3) the ewe shows no interest in her lamb. A total of 19 453 MAS were collected over 12 years, across 24 farms (including both indoor and outdoor lambing systems) and 12 different breed lines that make up the Innovis breeding programme. Ewe parity, breed, number of lambs carried, flock, lambing batch, lambing day within flock and pre-mating weight all had a significant effect on MAS (P < 0.05). The maternal assistance score was shown to be heritable (h² = 0.05) and repeatable (0.10), positively genetically correlated to lambing difficulty (rg = 0.29) and amount of assistance the lamb required to suckle from the ewe (rg = 0.88), and negatively genetically correlated with the number of lambs successfully reared (rg = 0.49). This study shows that an easy-to-measure score can be used by shepherds with large breeding flocks, based on whether the ewe requires further assistance to support her lamb rearing. The score could be used in breeding programmes to select for lamb rearing ability in the future and potentially lead to an improvement in lamb welfare through a reduction in mortality.

Keywords: Genetic parameters; Heritability; Lamb survival; Maternal behaviour; Scoring system.