Review of genetic studies of susceptibility to facial eczema in sheep and dairy cattle

Abstract

Genetic responses of sheep and dairy cattle to the hepatic mycotoxin, sporidesmin, were reviewed. The mycotoxin can lead to clinical facial eczema (FE) in the most susceptible and severely challenged animals. The extent of hepatic injury is normally assessed from an enzyme secreted into the blood, gamma-glutamyltransferase (GGT). Latest heritability estimates for the natural logarithm of GGT level, 21 days or more after a sporidesmin challenge, were 0.45±0.03 in sheep and 0.34±0.02 in dairy cattle. Clinical FE follows from phylloerythrin (from chlorophyll) spilling over from the bile duct. Upon exposure to sunlight, phylloerythrin absorbs ultraviolet radiation, becoming reactive. Neither its concentration in blood nor clinical cases of FE are likely to be good indicators of liver damage from FE for ranking sires. Gaps in knowledge about genetic factors relating to FE susceptibility are highlighted. © 2013 The Royal Society of New Zealand.