Associations between lamb growth to weaning and dam udder and teat scores.

Aims: To investigate associations between lamb growth to weaning and dam udder and teat scores measured at pre-mating, pre-lambing, docking and weaning. Methods: Mature Romney ewes (n = 1,009) were enrolled from a commercial sheep flock located near Masterton, in the Wellington region of New Zealand in 2017. A range of udder and teat traits were scored in all ewes, using visual assessment and palpation, at pre-mating, pre-lambing, docking and weaning. During the lambing period, each newborn lamb was matched to its dam and lamb sex, birthweight and birth-rank were recorded. A rearing rank was allocated to each live-lamb at weaning, when all lambs were weighed (n = 1,570), allowing calculation of daily growth rates (g/day). Associations between udder and teat scores and lamb growth rates to weaning were examined using multivariable models for each udder-scoring time. Results: Growth rates of lambs whose dams had udder palpation scores of hard, or both teats recorded as abnormal, pre-mating were lower than lambs whose dams had normal scores (229.9 (95% CI = 213.2-246.6) vs. 254.5 (95% CI = 245.6-263.5) g/day; p = 0.011) and (227.4 (95% CI = 208.3-246.6) vs. 247.9 (95% CI = 235.7-260.2) g/day; p = 0.024), respectively. Growth rates of lambs whose dams had clinical mastitis at docking or weaning were lower than those without mastitis (215.8 (95% CI = 199.9-231.7) vs. 235.4 (95% CI = 225.4-255.0) g/day; p = 0.007) and (220.0 (95% CI = 205.2-234.8) vs. 254.7 (95% CI = 248.9-260.5) g/day; p < 0.001), respectively. Growth rates of lambs whose dams had asymmetrical udders at docking or weaning were lower than lambs whose dams had symmetrical udders (204.6 (95% CI = 189.7-219.5) vs. 240.2 (95% CI = 225.4-255.0) g/day; p < 0.001) and (223.3 (95% CI = 213.9-232.7) vs. 242.2 (95% CI = 229.4-255.0) g/day; p = 0.014), respectively. Conclusions and Clinical Relevance: Pre-mating udder palpation and teat palpation scores can be used to identify ewes whose lambs are predicted to have lower growth to weaning. Assuming a mean lamb age at weaning of 84.4 days, lambs born to ewes with a pre-mating score of hard would be expected to have a mean weaning weight that was 2.1 kg less than those whose dams had normal scores. Udder palpation, udder symmetry and clinical mastitis scores during lactation were also associated with lamb growth rates. Abbreviation: CALW: Conceptus-adjusted liveweight.