Low Lambing Percentage Caused by Fusarium
Zearalenone: If you have a persistent problem with poor conception rates, suspect Zearaleone.
Zearaleone is produced by several related species of fungi called Fusarium. These fungi produce several families of toxins,which may affect animal heath and productivity. One, an oestogenic mycotoxin that, like the contraceptive pill temporarily stops the ovulation rate is called Zearalenone.
This toxin can be converted by microbes in the rumen and by the animal into several related toxins which act like anabolic steroids (talenol, zeranol) oestrogens (a- and b- zearalenol) that are more potent than the parent zearalenone.
Zearalenone has been found in paddocks from North Cape to the Bluff, sometimes in sufficient quantities to reduce lambing percentages from 5 to 50%.
It appears in pasture from January onwards, gradually increasing to a peak in March or April, dropping off in July. It thus coincides with the mating of sheep, causing increased numbers of dry (barren) ewes.
Sheep are particularly sensitive to zearalenone and intakes of as little as 1 mg a day for 10-20 days prior to mating will reduce lambing by about 5%. If either the daily intake or duration of exposure increases, then the number of ewes that do not ovulate increases and the number of ewes with multiple ovulation decreases.
Where flocks are exposed to high zearalenone intakes throughout the mating, more barren ewes and fewer twins can be experienced. The reduced ovulation rate means that fewer ewes can be become pregnant during the first and second cycle of mating so while lambing percentages are not always reduced, lambing is often delayed with more lambs born late, making management more difficult.
Survey results confirm that zearalenone intoxication is a major cause of poor reproduction performance in many flocks.
Unfortunately the story does not stop there. Zearalenone is not the only toxin produced by Fusarium. Dr. Neale Towers' research group at Ruakura found that other toxins produced (by the tongue twisting name of Trichothecenes) by Fusarium are the cause of poor growth in lambs (autumn ill thrift), diarrhoea and suppression of the immune system among other problems.
Fusarium produce these toxins in laboratory cultures along with zearalenone so it is possible, that they also produce them, when they grow and produce zearalenone in pasture.
The research group at Ruakura is analysing pastures from farmers with ill-thrift problems to see whether trichothecene toxins are present.
In short, this fungus is bad news and the toxins caused by it, contribute to one of the major unsolved problems in New Zealand grass farming and it costs the country millions of dollars. (every one percent in lambing percentage or one kilo increase in pre slaughter lamb weights is worth $ 10 and $25 million respectively in overseas earnings).
To top it all of zearonal -one of the products formed in the gut from fusarium- is also used as growth promoter and in 1995 the French stopped a NZ lamb shipment after founding minute quantities of zearanol in the meat. Although the French did not believe, that the stuff naturally occurs in our pastures, research in New Zealand and overseas has clearly shown that this is the case.
Dr. Towers has tried to develop a vaccine and has worked with other scientists to find an enzyme that would turn the fusarium toxins into something harmless. Without success so far.
So what can we do about it?
Fusarium like Pithomyces charterum (FE causing fungus) lives in the bottom of the pasture on dead plant material. The only option at the moment for reducing losses depend on managing pastures to reduce dead matter production and adopting grazing practices that maximise green leaf intake and minimise indigestion of contaminated dead material. Sheep, if given the opportunity will selectively eat the green portion, avoiding the contaminated dead material.
A fast rotation will prevent ewes from grazing too low. The higher pasture intake will promote weight gain and thus the ovulation rate. Avoid pastures that "got away" in spring or early summer e.g. with a high content of dead litter.
Some grasses such as tall fescue have generally lower Fusarium and zearalenone levels, as do crops, chocory, red clover (of the low phyto-oestogen variety ) or brassica's. Mating ewes on these crops can increase lambing percentages even in years when zearalenone lewvels are low.
Fusarium fungi are so common in our pastures and high zearalenone levels so widespread that resulting production losses may make this the most important mycotoxin disease, causing even greater losses than Facial Eczema.
Due to the lack of research funds no research is carried out at the moment (Society of Animal Production, Dr. N. Towers, Ruakura Research Centre).