In 1986 Kikitangeo entered a programme to breed sheep that could withstand a FE challenge. The word tolerance is used to describe sheep that have some resistance to this disease. By 1986 it had been known for many years that steady progress into developing tolerance can be made by testing potential sires and using the most tolerant. This testing practice involves inserting a tube into the sheep’s stomach and giving a measured dose of a highly toxic substance know as synthetic sporidesmin. This is the equivalent of giving sheep a field challenge on pasture where FE spores are present, however the measured dose is much more accurate. Three weeks later a blood test is taken to measure the GGT level which indicates the level of liver damage. Many ram breeders start with a dose rate of 0.8 and gradually increasing this dose over a number of years. The most tolerant flocks in NZ are testing to 6.0 or a little over. In our latest test (2010) a dose of 4.0 was given to 10 rams. Six had a nil reaction and two were marginal and slight. (The two other categories are moderate and severe; sheep with a severe reaction are likely to die as a result of the dose)
Given the 2010 results, we are confident that this does rate can be significantly increased over the next few years. Kititangeo has over the years, used sires testing between 4.5 and 6.0, from other ram breeders, notably, Keith Abbott and John Reeves. The cost of testing rams, including veterinary costs is around $200 per sheep. It is very difficult for a ram breeder to test a top sheep knowing he may be unusable or worse.
Sadly, some ram breeders claim that their rams are totally tolerant to FE, which has led their clients to believe their flocks would be immune to this disease, even in years of high challenge. The result has been that a number of these farmers, several years ago, especially in East Coast regions, had considerable losses because precautions were not taken. In most years of moderate challenge, flocks using tolerant sires over a number of generations will have a fair degree of immunity. However, in years of high challenge – especially over a prolonged period – even the most tolerant flocks will suffer losses and liver damage unless precautions are taken.