A genetic analysis of lamb survival to different time points and reasons for lamb death

Poor lamb survival is a major cause of productive inefficiency in the sheep sector. Lamb survival rates vary dramatically between flocks and farm systems (such as the amount of labour and supervision during lambing, whether the flock is lambed indoors or outdoors); however, it is estimated that 10–20% of lambs die before weaning every year. Improving lamb survival could have an important impact on farm finances, farmer morale, welfare of the animals and the environmental impact of the sheep sector. This study aims to look at different ways of analysing lamb survival, to assess whether there is potential for trait definitions and recording protocols to be put in place that could lead to faster genetic gain and to investigate whether a farmer-assigned cause of death could be useful in the genetic analyses. Lamb survival to three age points: 48 h, 8 weeks and ultrasound scanning (∼125 days) was studied. The farmer-assigned causes of death investigated were dystocia, starvation due to mismothering or exposure (SME) and stillborn. The direct heritability of lamb survival to 48 h, 8 weeks and ultrasound scan was 0.03, 0.01 and 0.01, respectively. The maternal heritability was 0.05 for all 3 time points. The direct heritabilities of the farmer-assigned causes of death were not significantly different from zero; the maternal heritabilities were significantly different from zero. The heritabilities were 0.10, 0.02 and 0.06 for dystocia, SME and stillbirth, respectively. Both direct genetic effect and the genetic effect of the dam for survival to 48 h could be used in future breeding programmes and indexes to select for lines that have higher lamb survival, although with a low heritability, this will be slow. The genetic effect of the dam on survival to 8 weeks and/or ultrasound scanning should also be considered for inclusion in the analysis of lamb survival, to increase the accuracy of selecting breeding stock with genetic potential to improve lamb survival and allow faster genetic improvement in this trait.