Investigating associations between lamb survival to weaning and dam udder and teat scores.

AIMS: Firstly, to examine a range of udder and teat traits in Romney ewes and to describe the frequency with which different scores occur. Secondly, to investigate associations between lamb survival to weaning and ewe udder and teat scores.

METHODS: Mixed-age, mature Romney ewes (n = 1,009) were enrolled from a commercial sheep flock located near Masterton, Wairarapa, New Zealand in a prospective observational study, starting in January 2017. Ewes had a range of udder and teat scores measured at key management times: pre-mating, pre-lambing, docking and weaning. The udder and teats of each ewe were scored using both visual assessment and hands-on palpation techniques, with ewes in both standing and sitting positions. During the lambing period each newborn lamb was matched to its' dam, with lamb mortalities recorded throughout lactation. The predictor variables for modelling were udder and teat scores (measured at the ewe level), while the outcome variable was lamb survival to weaning (measured at the lamb level). At each time point, univariate screening was conducted, followed by multivariable generalised estimating equation model development.

RESULTS: Ewe pre-mating udder palpation scores were predictive of failure of their offspring to survive to weaning. The offspring of dams with 'lump' or 'hard' udder scores had 4.9 (95%CI 2.6-9.6, p = 0.003) and 3.0 (95%CI 1.5-6.1, p < 0.0001) increased odds of failure to survive, respectively, compared with lambs whose dams had 'normal' udders pre-mating. Clinical mastitis and udder symmetry scores at docking and weaning were explanatory of failure of lambs to survive to weaning. Lambs born to ewes that had mastitis at docking or weaning had 3.0 (95%CI 1.5-5.9, p = 0.001) and 3.9 (95%CI 1.3-11.6, p = 0.013) increased odds of failure to survive, respectively, compared with lambs whose dams did not have mastitis. Offspring of dams with asymmetrical udders at docking or weaning had 3.3 (95%CI 2.2-4.9, p < 0.0001) and 2.5 (95%CI 1.5-4.0, p < 0.001) increased odds of failure to survive, respectively, compared with lambs whose dams had symmetrical udders.

CONCLUSIONS: If commercial farmers wish to identify and cull ewes with unsuitable udders, the optimal time would be prior to breeding. At this time point, the best measure to use is udder palpation score. Subsequent to this, farmers can use clinical mastitis scores and udder symmetry scores to identify ewes whose lambs have greater odds of failure to survive to weaning in the present season; however, recommendations regarding culling these ewes are unclear and further longitudinal studies are required.