Examining udder and teat traits in Australian Merino ewes: genetic variance recorded within and across lactations

Context Reducing neonatal lamb mortality remains a major challenge globally, and early survival is strongly influenced by the ewe’s ability to provide adequate colostrum and milk. Udder and teat traits have been shown to affect lamb growth and survival; however, their genetic parameters are not well defined in Australian Merinos, particularly regarding how these traits change within a lactation and over the ewe’s lifetime. Aims This study aimed to estimate preliminary genetic parameters for four visually scored traits, udder depth, udder cleft, teat size and teat placement, recorded at lambing and weaning within a single lactation, as well as across age classes. Methods A total of 1257 ewes were scored at both lambing and weaning, and longitudinal records were collected from 2 to 6 years of age to assess the stability of the traits across lactations. Key results Heritability estimates were low to moderate (0.11 ± 0.04 to 0.42 ± 0.09) both within lactation and across age stages, indicating these traits have potential to be improved through selection. Genetic correlations between records taken at lambing and weaning were moderate to high (0.59–0.95), suggesting that most traits are consistently expressed throughout the lactation. Similarly, high genetic correlations (≥0.90) across age classes indicate that udder and teat traits are genetically stable across the ewe’s productive life, perhaps except for teat size, which showed lower correlations between early and later life measurements (0.70). Conclusions Together, these findings imply that a single recording at either lambing or weaning may be sufficient to capture an animal’s genetic merit for udder depth and teat placement. However, repeatability across age stages was low to moderate (0.21–0.29), suggesting that multiple assessments over successive lactations may still improve the accuracy of selection, particularly for teat size, which showed greater variability in genetic expression with age. Implications The estimates within this study provide sound foundational knowledge for how genetic variation in udder and teat traits changes over time in Merino sheep, which have been selected for wool and meat production rather than milking ability.