Genetic and environmental causes of variation in mastitis in sheep

Abstract

The purpose of this investigation (1982–1988; 920 ewes, 2364 records) was to determine incidence of mastitis, different factors affecting mastitis, genetic variation of the trait for the possibility to include mastitis in breeding plans of sheep and reduction in lambs' live weight caused by mastitis of the ewe. Mastitis was recorded by visible and palpated changes, plus relevant supplementary factors. Overall frequency of mastitis was 6.8% and uniform between years. Incidence of mastitis increased with number of lambs born. There were significant differences between Norwegian sheep breeds. Steigar sheep had the highest incidence, and a selected line for high litter size and Spel had the lowest. Ewes kept on mountain pasture had a lower incidence than those kept on cultivated pasture. According to udder score given to the ewes by the time of lambing, ewes that had bad udder conformation had a much higher incidence of mastitis. Heritability estimated from ewes' resistance to mastitis, i.e., how many years the ewes produced without coming down with mastitis, was estimated to be 0.13 (±0.16) by the LS-method and 0.49 by the nonlinear threshold method. Average reduction in the weaning weight because of mastitis was approx. 4 kg.