Ewe udder and teat traits as potential selection criteria for improvement of Merino lamb survival and growth

Neonatal lamb mortality is a major economic and welfare issue for Australian sheep producers. The contribution of udder and teat traits of the dam to the survival and subsequent growth of the lamb is relatively unknown. This study aimed to estimate phenotypic and genetic parameters associated with objectively measured and visually scored udder and teat traits in Australian Merino sheep, and to evaluate the impacts of udder and teat traits of the dam on survival and growth of their lambs to weaning. Ewes from the New England Merino Lifetime Productivity flock (n = 1341 ewes) were assessed for udder and teat traits, and phenotypic and genetic parameters for individual traits and relationships among them were estimated using linear mixed models. Odds ratios were calculated to investigate the influence of udder soundness on lamb mortality. Further, the influence of udder traits on variation in lamb weaning weight was explored. Measured udder and teat size traits were estimated to have moderate to high heritabilities (0.32 (0.09) to 0.56 (0.10)), while the heritabilities of visually scored traits were lower (0.09 (0.05) to 0.17 (0.07)). Measured traits were highly correlated genetically with their equivalent visually scored traits. The odds ratio of mortality for lambs born to ewes with unsound versus sound udders was 1.54 (95 %CI 1.1–2.2, P < 0.05). The odds ratio of lamb mortality from starvation compared to all other causes of death for lambs born to ewes with unsound versus sound udders was 4.62 (95 %CI 2.4–8.9, P < 0.001). Dam udder and teat traits collectively contributed 8 % of the variation in lamb weaning weight observed. Results suggest that targeting optimal ewe udder and teat characteristics in sheep breeding programs has the potential to significantly improve lamb survival and growth in extensive production systems.