GENETICS OF SUSCEPTIBILITY TO FACIAL ECZEMA IN FRIESIAN AND JERSEY CATTLE

A total of 528 calves from 3 calf crops, sired by 34 Friesian and 28 J ersey bulls, were challenged with sporidesmin, the toxin causing facia l eczema (FE), in order to determine the genetic variation in suscepti bility to FE. The challenge was either by grazing toxic pasture or by oral dosing, and the response was monitored by blood sampling to measu re the elevations of serum gamma-glutamyltransferase (GGT), glutamate dehydrogenase (GDH), and other possible indicators (enzymes or metabol ites: bilirubin, aspartate transaminase, ferroxidase, bile acids, and S'nucleotidase). The last calf crop was shed, in part, by bulls phenot ypically selected from the second calf crop using GGT records. Data we re analysed using the repeated records option of a restricted maximum likelihood programme. A sire model was used, with sires and maternal g randsires included to determine pedigree. The uni-variate heritability estimates for log(e)GGT were 0.29 +/- 0.15 in Friesians and 0.77 +/- 0.13 in Jerseys, and for log,GDH they were 0.20 +/- 0.12 and 0.64 +/- 0.13, respectively. Corresponding repeatabilities were 0.86 +/- 0.01 a nd 0.84 +/- 0.02 for log,GGT, and 0.66 +/- 0.03 and 0.69 +/- 0.03 for log,GDH. The genetic correlations between the two enzymes were 0.99 fo r Friesians and 0.95 for Jerseys. Genetic correlations between the fiv e other enzymes or metabolites and log(e)GGT were generally high (0.79 to 0.99), with the exception of ferroxidase which was not correlated with log(e)GGT. The next best indicators of FE susceptibility after GG T and GDH were aspartate transaminase and 5'nucleotidase, which were p henotypically correlated with GGT, were heritable (in Jerseys) and rep eatable, and showed elevation in response to challenge. The ''High'' a nd ''Low'' GGT-selected sire groups in the last calf crop had signific antly different progeny mean GGT levels in both breeds. It was conclud ed that selection against high GGT concentrations following FE challen ge should reduce the susceptibility to FE in subsequent generations.