Usefulness of subjective ovine milk scores: I. Associations with range ewecharacteristics and lamb production

Range ewes are commonly evaluated for milking ability by producers to deter mine the ewe's ability to rear lamb(s). The U.S. Sheep Experiment Station h as subjectively scored (low, average, high) a ewe's milking ability within 24 h of lambing for many years. The relationship of subjective milk scores with lamb production was investigated using lambing records of Columbia (n = 1,731), Polypay (n = 1,129), Rambouillet (n = 1,704), and Targhee (n = 1, 638) ewes. The incidence of high milk scores increased from less than 10% a t first parity to 29 to 40% at second and greater parities. At maturity, Co lumbia ewes (38%) had the highest percentage of high milk scores. A positiv e association existed between ewe BW and her milk score at third and later parities. Ewes with high milk scores gave birth to heavier lambs (P < 0.05) , whereas ewes with low milk scores were associated with lighter (P < 0.05) lambs at birth. Ewes with low milk scores weaned less (P < 0.05) total wei ght than ewes with better milk scores across all age groups for all breeds. Lighter weaned litter weights from ewes with low milk scores were linked t o lighter birth weights and fewer weaned lambs. Differences for Litter weig ht weaned between ewes with average and high milk scores were generally obs erved at 2 and 3 yr of age, when litter weights were heavier among ewes wit h high milli scores (P < 0.05) for all breeds. Between the ages of 1 and 3 yr, Columbia, Polypay, Rambouillet, and Targhee ewes with an average milk s core weaned heavier (P < 0.05) litters (average differences of 10, 9, 13, a nd 12%, respectively) than ewes with low milk scores. For all breeds at all ages, individual lamb weaning weights were heavier (P < 0.05) when they we re reared by ewes with high milk scores compared to lambs reared by ewes wi th low milk scores. Results suggest that milk score is an economically impo rtant trait in these four breeds and should be considered in management and breeding objectives; at a minimum, the incidence of low milk scores should be kept as small as possible.