Zearalenone is a fungal toxin produced by Fusarium species commonly found on autumn pastures in New Zealand, and it may interfere with reproductive functions in sheep. We have measured both ovulation rate after challenge with zearalenone, and also a metabolic indicator, Zen/Cr (the concentration of zearalenone and its breakdown products (Zen) in urine, after adjustment for urinary volume using creatinine concentration (Cr)). A small self-replacing flock of Coopworth ewes was used for the study. This paper reports a preliminary assessment of whether Zen/Cr might be an equivalent but cheaper method than laparoscopic ovulation rate for measuring an animal`s resistance to zearalenone. Ovulation rates were determined in ewes in autumn before dosing (Lap1; Years 1 and 2), and after dosing (Lap2; Years 1 to 4) with 10 mg zearalenone per animal per day for 6 days. The average reduction in ovulation rate following dosing (Years 1 and 2: Lap1 minus Lap2) was 0.60 ovulations or 31% of the mean. Lap2 was used for the present correlation analyses. The heritability of Lap2 was estimated (0.11 ± 0.09), and breeding values (BVs) for Lap2 were determined. Subsequent to the laparoscopy, the ewes were mated at pasture, and the resulting natural litter sizes were monitored in relation to BVs for ovulation rate after challenge. Urine samples were taken during and after dosing in Years 3 and 4, to measure Zen/Cr, and a heritability for Zen/Cr (0.32 ± 0.10) was estimated from these and other Zen/Cr data. Preliminary analyses of BVs for Lap2 and Zen/Cr revealed a negative correlation between them (r = - 0.55). Ewes with higher BVs for ovulation rate also had higher mean litter sizes following natural ovulation. In conclusion, zearalenone affects ovulation rate at moderate challenge levels, and this ovulation rate may be negatively related to the concentration of measurable urinary zearalenone metabolites. KEYWORDS: sheep; zearalenone; dose rate; ovulation; heritability.
Proceedings of the New Zealand Society of Animal Production, Volume 65, Christchurch, 320-323, 2005
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