2023-07-26, Smith, E G, Acton, G A, Bell, A M, Smith, J L

In Australia, there is currently no standard system for assessing ewe udder traits for genetic improvement. The aim of this study was to provide preliminary genetic parameter estimates of four visually scored udder and teat traits recorded at lambing and weaning, to inform recommendations about how and when to record udder and teat traits. Udder depth, teat size and teat placement were moderately heritable at both lambing and weaning (0.23 ± 0.08 to 0.36 ± 0.09) and the traits recorded at the two stages showed high genetic correlations (udder depth 0.75 ± 0.14; teat size 0.79 ± 0.12; teat placement 0.70 ± 0.16). Udder cleft, showed lower heritability, and lower genetic correlation across the two stages, with increased phenotypic variance from lambing to weaning. These results suggest that either stage is appropriate for recording udder depth, teat size and teat placement for genetic improvement of Australian Merinos.

2023-07-26, Smith, E G, Walkom, S F, Clark, S A

The ability to select sheep which have a greater capacity to overcome environmental fluctuations is topical given the severity of climatic events, labour shortages and increased productive demands (lamb, meat and wool). In this paper, we review the possibility of using variation in fibre diameter (FD), measured along the wool staple as an indicator of how sheep respond to the fluctuations of their environment.

2023-08, Smith, E G, Walkom, S F, Brown, D J, Clark, S A

The capacity to measure and select livestock that are more resilient to environmental fluctuation is of increasing importance amidst climate change, labour shortages and increasing production demand. Currently, however, there is no consensus on how to quantify resilience, particularly in extensive sheep populations. In this study, we explored the ability to derive resilience indicator traits from fibre diameter variation measured longitudinally (5 mm increments) along the wool staple. Fibre diameter varies in relation to the supply of nutrients to the wool follicles and thereby provides a stable archive of the animal's physiological status across the preceding wool growth period. From this fibre diameter variation, ways to detect and characterise an animal's ability to withstand or be minimally affected by its environment were explored. The heritability estimates of these traits were shown to be low to moderate (0.10 to 0.31), indicating that genetic variation exists for fibre diameter variation measured along the wool staple which may be interpreted as a measure of resilience. The inclusion of such measures in sheep breeding programs has the potential to improve the resilience of sheep to environmental challenges, which may have positive implications for sheep enterprise profitability, health and welfare.

2023-08, Smith, E G, Hine, B C, Acton, G A, Bell, A M, Doyle, E K, Smith, J L

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.