Palpable udder defects are associated with decreased lamb production in commercial ewes

Abstract

In pasture-based sheep production systems total weight of lamb weaned impacts flock profitability. Udder defects have been associated with poor lamb survival and lower lamb growth rates to weaning in non-dairy breed sheep. However, it is the combination of these two factors that influences ewe flock productivity and value to the farmer. The objective of this study was to describe associations between ewe udder palpation (normal vs. abnormal; where abnormal is diffuse udder hardness, or palpable lumps(s), on one or both udder halves), and total kilograms of lamb weaned. Mixed-age Romney ewes were enrolled from a commercial sheep flock located near Masterton, Wairarapa, New Zealand, in a two-year prospective observational study; 981 ewes in 2017 and 790 ewes in 2018. In each year, ewes had their udders palpated at four key management times (pre-mating, pre-lambing, tailing and weaning). During the lambing period, twice daily lambing observations were undertaken to match lambs with their dams, while at weaning in each year total weight of lamb weaned per ewe was calculated (where kilograms of lamb weaned equalled the sum of the weight(s) of live offspring at weaning). Analyses used matched methods for each time udder palpation occurred. Each ewe with an abnormal udder was matched to four ewes with normal udders, based on: parturition date, number of lambs born in the litter, and ewe weight and body condition score prior to lambing. The prevalence of ewes with abnormal udder palpations ranged from 2.7% - 7.7% at each of the measurement times. At all management times, ewes that had abnormal udder palpation weaned significantly less total kilograms of lamb compared to ewes that had normal udder palpation. Importantly, pre-mating udder palpations were predictive of total weight of lamb weaned. Ewes with normal udders pre-mating weaned an estimated mean of 42.2 kg and 45.4 kg in 2017 and 2018 respectively, while ewes with abnormal udders weaned 25.8% less lamb (p<0.0001) in 2017 and 33.2% less lamb (p<0.0001) in 2018. These results suggest commercial farmers could use udder palpation prior to mating as a tool to identify and prioritise culling of ewes with palpable udder defects, as these ewes are predicted to have lower lamb production.