The Fungus

·      Zearalenone, (pronounced zeer al en own), is a fungal toxin produced by the fungus Fusarium. It is also called F-2 toxin.

·       Fusarium is the name given to a large group of fungi.  They occur through out New Zealand.

·      The fungi have been found in numerous feeds including pasture, maize, barley and other feedstuffs. The Fusarium  associated with ewe infertility is a saprophytic fungus, this means it grows on dead material, that preferentially grows on dead litter at the base of the pasture.

·      The maximum growth is during warm dry conditions, i.e late summer and the autumn. Spores are formed under warm dry conditions.

·      High zearalenone levels occur under a wide range of weather conditions so high risk times are difficult to predict.

·      Spore counting is of no value.

Effect on Oestrus Behaviour

·      The toxin produced is oestrogenic, and results in ewes that absorb the toxin having changes in their oestrus behaviour (heat) and a reduction in ovulation and fertilisation rates. The ewes have a shorter cycle length and an increased duration of heat.

·      This results in a decreased lambing percentage via an increased number of barren ewes and fewer multiple births.

·      Lambing percentage falls by about 5% for every mg of zearalenone ingested per day. This occurs after 10 to 15 days of grazing zearalenone toxic pasture. Exposure for a longer duration results in increased depression of lambing percentage.

·      The oestrogenic effects also effect males, with reduced libido, testicular atrophy and reduced sperm production. The significance has not been proven in New Zealand.

·      In cows enlarged mammary glands, and prolapse of the rectum and vagina are symptoms. This may have some relevance to prolapses in ewes.

Diagnosis

·      Suspect a problem if scanning or lambing percentages are inconsistent with mating weights after excluding other obvious problems.

·      Pasture samples will indicate the presence of zearalenone. One ppm in a bulk grass sample appears to be a toxic level for ewes. Studies indicate 3mg/ewe/day is toxic.

·      Urine testing for a zearalenone metabolite, zearalenol is the best indicator.

·      Prediction of the severity can be made, as urine zearalenol increases with increased zearalenone intake.

·      Urine from 12-15 ewes should be collected and bulked together. Importantly an equal quantity from each ewe is bulked together. 0.5 to 1 ml each is sufficient.

·      Methods of collection of pasture, urine and sample handling is best discussed with the clinic.

·      The effect is worst the greater the amount and length of exposure.

Prevention

·      No treatment or vaccination for zearalenone is available

·      Resistance to facial eczema does not confer resistance to zearalenone.