Friday, July 1, 2022

Link to false positives no fluke

The West Coast of the South Island gets more false positives in bovine tuberculosis (Tb) testing than the drier east coast and it prompted a high-school teenager to investigate the link with liver fluke.

Coast and he has long been concerned about the number of two-year-old heifers that showed no sign of Tb at slaughter after previously testing positive.

His Year 11 daughter, Heather, took the issue up as a science project and investigated whether the parasite Fasciola hepatica, more commonly known as “liver fluke”, could be a possible cause of the false reactions. She analysed data she collected from West Coast dairy farms, as well as examining liver fluke samples under the microscope, searching for bacteria that might contribute to false reactions.

"The general consensus from the farmer survey was that liver fluke was a major issue for the majority of West Coast farmers, presumably because the wet climate is ideal to support the parasite's life cycle,” she said. “Only one or two of the farms had never had liver fluke and they were on higher ground with better drainage.

"And on the West Coast a disproportionate number of young heifers that react to Tb skin tests are found to have no Tb lesions at slaughter."

Heather made a request to dairy farmers for information through Westland Milk Products and although there was insufficient feedback to make definitive conclusions, she said there was potential for a correlation between liver fluke in a herd and false Tb reactors.

Mark said it was a concern that a considerable number of young heifers never made it into the milking herd because they were slaughtered as test positive reactors.

"They react to the skin tests and blood tests, but still a significant number go through to slaughter and don't have lesions.

"Animals are occasionally required to be killed on farm and a high proportion of those without lesions have liver fluke infestations."

Many farmers conducted bulk milk tests for liver fluke and were treating their young animals after Tb testing had been completed, which meant the animals would be tested with a fluke burden, he said.

“If some of the causes for non-specific reactions can be identified through further investigation, this could reduce the amount of animal wastage of young stock from the industry. There's also potential to save in terms of compensation payments for reactors.”

If liver fluke infestation was found to be an important cause,  Neal said it might be a simple matter of changing the timing of treatment in relation to the Tb skin tests to reduce the number of false reactors. However, more research was required to reach a more solid conclusion.

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