Thursday, March 28, 2024

Waging war against infectious disease

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Infectious disease costs the rural economy more than $500 million a year, Otago University scientist Professor Frank Griffin says.
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Losses of $300m in the dairy sector alone were running at $50 a cow a year, Griffin said.

Johne’s disease was draining at least $100m from the cattle, sheep and deer sectors through lost production, reduced fertility, and deaths. Dairy farmers were dealing with capital losses of more than $100,000 a year each from Johne’s.

The annual cost of bovine viral diarrhoea was sucking out more than $50m in losses and disease surveillance, while a 2005 Dairy Insight study estimated mastitis was draining $180m from the dairy sector.

Annual losses in the sheep industry attributed to salmonella were put at $10m.

Modern breeding programmes for domestic livestock had selected a restricted gene pool of animals with superior production traits which, combined with increasing intensive farming practices, could result in increasing levels of susceptibility to infectious diseases, Griffin said.

“Animal health and infectious disease remains the single-most-important arbiter of farm profit in New Zealand’s future.” 

Optimal health control strategies had a positive impact on all facets of a farming business, its efficiency, productivity, sustainability, and the wellbeing of animals, he said.

“In addition, accreditation of food products derived from healthy livestock is being increasingly sought by consumers. It mitigates against non-tariff trade barriers and adds intangible value to the NZ brand. 

NZ’s future economic prosperity continued to be heavily reliant on the productive capacity of its farming sector, reinforcing the need for selecting animals with superior resistance to disease, Griffin, who is working on Johne’s disease, said.

Johne’s could have a devastating impact on dairy herd profitability through direct costs of culling affected animals, reduced production rates, poor reproductive performance, and increased susceptibility to other disease, he said.

Vetlife Temuka veterinarian Andrew Bates said some herds were so heavily infected with Johne’s the number of cows being culled ran into double digits each season. 

Control had traditionally been challenging, he said. Though diagnosis was straightforward once clinical signs were evident, early detection of animals in the pre-clinical stage had been unreliable.

Detection before animals passed millions of infective bacteria in their dung but were not showing obvious signs of infection was the key, Bates said.

“In this way Johne’s disease is an iceberg phenomenon, where often the clinical cases seen represent just a small fraction of the infectious load on the dairy farm.” 

Griffin and colleague Simon Liggett have been working for many years on solutions to control Johne’s in the deer industry and are beginning to transfer some of their knowledge and experience to the dairy sector.

In a collaborative effort with Vetlife, a comprehensive Johne’s control programme was being used on individual dairy herds, aiming to accredit milk products as being free from Johne’s, Griffin said. 

Griffin and his research team have developed a platform for cost-effective Johne’s diagnosis in high-producing dairy herds.

It involved coupling several new-found diagnostic markers with the cow’s body condition score and milk yield to identify diseased animals for culling.

Bates and his colleagues are working with a number of dairy farmers who have high endemic levels of Johne’s disease in their herds.  

The process began with blood testing the entire dairy herd to identify cows most likely to pass Johne’s bacteria in their dung, Bates said.

Those animals were then dung sampled to confirm their status as shedders, so they could be removed from the herd as quickly as possible.

Griffin said frequently the list of shedders contained animals that looked normal, because the testing identified problem cows before they had developed obvious signs of clinical disease.

By removing those high shedders the infectious pressure in the dairy farm was reduced, resulting in the number of newly infected animals dropping year on year.

Suspect animals, though not shedding, could also be identified, he said. 

Body condition score, dung consistency, and milk production were monitored, to maintain the cows as productive members of the herd for as long as possible but to remove them before they became shedders.

The suspect animals were also marked, so their colostrum was not fed to the next generation of dairy heifer replacements. 

MORE: Read more in the October editions of Country-Wide and NZ Dairy Exporter.

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