Sheep farmers show the lead to dairy farmers on a genetic solution to FE

category Genetics

The facial eczema (FE) outbreak this season is a wake-up call.

Many farming in ‘safe’ areas have had a rude shock; even if they did implement prevention systems after FE became evident, they will have been too late as these systems must be in place before a facial eczema challenge.

Sheep farmers have utilised genetics as a tool to prevent FE for 30 years. In that time, AgResearch’s Ramguard service has been providing the sporidesmin toxin responsible for FE to ram breeders who annually challenge their ram hoggets for tolerance. Some of these breeders are now using dose rates 6 times higher than when they started and they experience very little clinical FE in their flocks today compared to what would have been the situation 30 years ago.

This season has also caught-out many dairy farmers who thought they had effective protection systems in place, using zinc in either the water supply or by drenching or by the application of boluses. This season was extreme in that the warm weather systems from late-January until mid-May have caused an almost continuous elevation of spore counts. Any delay in starting protection or a temporary breakdown in providing an adequate supply of zinc resulted in liver damage, and if this liver damage was severe enough, for a proportion of cows to exhibit skins lesions, the visible signs of clinical FE. However, it is the hidden disease, sub-clinical FE, which may come back to bite at calving when animals with damaged livers which have not healed substantially, will not be able to cope with the stresses of calving and lactation.

Unlike their sheep farming counterparts, dairy farmers have not utilised genetics as a tool to combat FE. At AgResearch, members of the genetics group have collected FE records on dairy cattle for 25 years plus. Analyses of this data shows the heritability of FE tolerance is at the same level as that for milk production traits and therefore genetic gain for tolerance is possible. But the dairy industry has shown little appetite to exploit this knowledge.

The exception is CRV Ambreed who have been working with AgResearch since 2002 in researching the application of genetics to FE in dairy cattle. In 2010, with funding from DairyNZ’s On-Farm Investment Fund, AgResearch ran a pilot trial where surplus bulls were given a measured dose of sporidesmin once and for some twice, to provoke liver damage in these animals and to investigate the variation in responses. Liver damage is measured by the levels in blood of an enzyme GGT which is routinely measured for indications of liver trauma.

After the success of this pilot trial, in 2011 AgResearch commenced the now ongoing work of directly challenging a proportion of each annual intake of young bulls for progeny-testing by challenging them with sporidesmin and analysing the results through its genetics software.

For the past 6 years, teams of bulls from those that showed no or very little response to the challenge have been marketed by CRV Ambreed and these sires are expected to leave progeny which will have GGT levels 25% lower than progeny of “average” sires – in other words sires unselected for FE tolerance. The genetics route is not an overnight fix as it takes time for the genes to spread through a population. But the effect of this year on year reduction of the level of susceptibility is that preventative treatments will be more effective and in time may not be required.

There may be a trade-off in terms of BW; currently bulls are chosen from the whole team of DNA-selected young sires and CRV Ambreed estimate that there would be a $20 BW drop in daughters of FE-tolerant sires compared to those born to top-ranking sires. However for a farmer who has a major issue with FE, this drop may be inconsequential compared to the reduction in milk production and animal losses caused by FE.

Dairy farmers clearly believe in the worth of genetics as evidenced by the majority of cows being sired by AB bulls. This season’s experiences may convince more farmers of the value of genetics for FE. Those who have any doubts should look to the sheep industry.

Photo: Glowing is one of CRV Ambreed’s Facial Eczema tolerant sires on market this year.

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