Abstract

Copper is a potent catalyst of the reaction in which sporidesmin generates damaging free radicals causing facial eczema in grazing livestock in New Zealand. This study sought to investigate whether circulating copper at the time an animal is dosed with the toxin, influenced the way the animal responds to sporidesmin and whether the action of sporidesmin on the liver in susceptible animals results in changes to circulating copper. Serum copper concentrations (CU) together with gamma glutamyl transferase (GGT) activity, an indicator of bile duct damage, were opportunistically collected on over 400 animals from nine flocks in which the animal’s tolerance to sporidesmin was commercially assessed through measuring its response to a known dose of the toxin. The association between CU concentration before the animals were dosed and natural log transformed GGT activity measured 21 days after the animals had been dosed was not significant, but there was a suggestive (P=0.06) interaction between flock and CU. There was a significant positive association between natural log transformed GGT activity and CU concentrations measured 21 days after the animals had been dosed with the toxin (P<0.0001). For some individuals, the CU concentrations approached or met copper-toxicity thresholds (above 40 μmol/L). The specific biological mechanisms causing this association remain unknown, but given the role of copper in catalysing the sporidesmin reaction and the potential of toxic copper concentrations, further research is warranted. Keywords: sheep; facial eczema; copper; gamma glutamyl transferase

Johnson, PL, and NC Amyes

New Zealand Journal of Animal Science and Production, Volume 80, Online, 34-38, 2020