Heritability of entropion in several US sheep breeds

Heritability for incidence of entropion was estimated in an experimental flock of purebred (Columbia (C), Polypay (P), Rambouillet (R), Suffolk (S), and Targhee (T)) and crossbred (from matings of Finnsheep rams with C, R and T ewes, from Merino X R matings, and from miscellaneous other matings) lambs. Data from 1986 to 1994 which included 39 440 records were analyzed using a multiple trait REML program with an Animal Model (AM). Overall mean incidence rate for entropion was 3.1% over a 9 year period, ranging from 1.1% in 1988 to 5.0% in 1989. Breed group ranking within each year was consistent, with overall mean incidence rates of 10.4%, 6.9%, 6.4%, 3.7%, and 3.3% for Suffolk, Merino-crosses, Columbia, Targhee, and Rambouillet groups, respectively. Purebred Polypay and Finn-crossbred lambs each had 1.0% overall incidence rate. For all breed groups analyzed together, the direct heritability estimate for incidence of entropion was 0.15. Heritability estimates for separate purebred groups were 0.21, 0.17, 0.10, 0.09 and 0.08 for C, S, T, R and P, respectively. It was concluded that selection against entropion can lower incidence rates, at least in Columbia and Suffolk breeds.