Friday, March 29, 2024

An eye to the future

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I took part in a recent facial eczema forum that considered, among other topics, areas for more research. This disease continues to be a significant cause of production losses in New Zealand and also has the potential to be a big animal welfare issue. 
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Many years ago I was involved in an attempt to set-up a sustainable farming standard. Diseases such as flystrike and facial eczema (FE) were big negatives against that guideline because both had significant animal welfare tags attached to them and are largely preventable. 

My working experience confirms FE is an expensive disease. Lowered performance is probably the biggest cost with the greatest expense in animals that show no outward signs of the disease. Lowered weight gains, lower conception rates, lowered lamb survival and a lower carcase value can all occur because of FE with no outward signs. Losses that happen because of animals with clinical signs can also be huge.

There are many options for managing FE, the most powerful being sheep that are bred to be FE-tolerant. At the forum I was pleased to hear about progress being made in breeding FE-tolerant cattle. Supplementing animals with reasonably large doses of zinc gives good protection and is widely used for cattle. However, apart from the cost there is evidence of lowered animal performance when loaded up with such levels of zinc. There are also mounting concerns around soil contamination because of excess zinc. 

Spraying pastures with fungicides is an effective way to minimise FE but application timing is critical and rain can be disruptive. But, as with any such blanket treatment, what else is being taken out with that fungicide? There are a multitude of valuable fungi living in pastures and soils that will be just as susceptible to the spray as Pithomyces is. The magic spray that can remove all lurking L3 larvae in pastures will also take out the multitude of beneficial worms that keep soils healthy.  

I know farmers who manage FE effectively by having a grazing plan. This means setting up grazing areas that don’t carry high levels of spores which might be southern faces, windy areas or growing crops. Whatever it is, there are management options that will reduce the risk. 

Too often, however, I see outbreaks of FE that have received warnings but where no action was taken to minimise the risk. Furthermore, I see all too often sheep in high-risk areas bred from rams that have had no selection for FE-tolerance. To buy tolerant rams might cost more but the benefits massively outweigh the costs. In other words, high-performing FE-tolerant rams are cheap for the benefits they bring.

The new kid on the block for selecting FE-tolerant sheep is DNA selection. This technology has progressed to the point where it’s a real option. Cost is probably the biggest barrier, but as a selection tool it is far preferable to dosing sheep with sporidesmin to find those that don’t react. A paper presented at the forum by an evolutionary scientist working with biomarkers and epigenetics fascinated me.

Both terms are quite technical, but a basic definition of biomarker I’ve found states: “Any substance, structure or process that can be measured in the body or its products and influence or predict the incidence of outcome or disease.”

When this is applied to FE it exposes processes in the sheep that can be measured and that relate to susceptibility to the disease. However, in the process of exploring these biomarkers the role of epigenetics became evident. Epigenetics is a broad term but essentially it’s the study of biological mechanisms that will switch genes on and off. For example, it seems an animal’s earlier exposure to sporidesmin alters its subsequent response. This is because the early exposure affects the controller genes, which in turn determine the reactivity to subsequent exposure. 

My poor understanding notwithstanding, this research struck me as being novel, groundbreaking and potentially very valuable for selecting tolerant animals. In my opinion, it’s one of the best allocations of funding in recent times. 

However, because it’s not from an animal health research budget, this funding will soon run out.

It must be time for interested parties – farmers, meat companies, animal health companies and agricultural scientists – to take over funding because it offers so much. The biomarker approach has many applications to other diseases and could lead to revolutionary solutions. The return on investment could be massive.

  • Trevor Cook is a Manawatu veterinarian.
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