Abstract

A project was designed to progeny-test dairy industry sires for their resistance to facial eczema (FE), as a preliminary step towards identifying DNA markers or genes for FE resistance. The FE disease is caused by the toxin, sporidesmin, produced by spores of a fungus, Pithomyces chartarum, found on many pastures in summer and autumn in the North Island of New Zealand. In susceptible animals, sporidesmin causes liver injury, and the cost of FE to the dairy industry is measured in tens of millions of dollars in years with serious outbreaks ($3.6 to 66.2M per annum). Earlier studies in New Zealand have established that resistance to FE in cattle is a heritable trait, with resistance measured by variation in activity in blood of liver-derived enzymes, gamma-glutamyltransferase (GGT) and the associated glutamate dehydrogenase (GDH). Widely used Friesian and Jersey sires were progeny-tested via 572 specially-reared sons (born in 2002-04 and dosed with sporidesmin), and also via 3761 daughters in autumns 2004 and 2005 in 17 herds with 3-22% clinical cases of FE per herd. The data were combined from all sources, including four earlier years of GGT records (1173 animals born in the 1986, 1989, 1990 and 1992 birth years), and standardisation was applied to each contemporary group. Heritabilities were estimated for Friesians (0.47 ± 0.07 for log GGT; 0.32 ± 0.08 for log GDH) and for Jerseys (0.37 ± 0.06 and 0.39 ± 0.09, respectively), and there was a very high genetic correlation between activities of the two enzymes (0.93 ± 0.03). Sixty-eight sires had reliabilities of >0.70 for log GGT Breeding Value and 71 others had reliabilities between 0.60 and 0.70. The sires progeny-tested in this way generally were already proven for dairy traits and had been widely used, so that FE selection among these sires would be an additional trait when they were already old. Alternative approaches would be to performance-test young bulls for FE resistance, or to use sire and progeny data and their DNA to identify DNA markers or genes for FE resistance.

NG, Cullen, CA Morris, and SM Hickey

Proceedings of the New Zealand Society of Animal Production, Volume 66, Napier, 310-314, 2006