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Selecting for Parasite Resistance - A New Tool

09 August 2012
Meat & Livestock Australia

AUSTRALIA - Research, funded by Meat and Livestock Australia (MLA) and led by veterinarian and Angus breeder Dr Peter Honey, has developed a new weapon against growing internal parasite resistance – genetics.

“A colleague who I worked with in the US alerted me to the excellent research being done in the famous Wye Angus herd. I’ve been following their progress for the past 10 years,” Dr Honey said.

“In this herd it was shown faecal egg count (FEC) is a phenotypic indicator of parasite resistance and this resistance is moderately heritable. Predicted differences – the equivalent to Estimated Breeding Values (EBVs) – were derived even in this relatively small herd.”

And even better, Dr Honey’s Australian research found no indications of negative impact on production traits by selecting for parasite resistance.

“The Angus Long Fed/CAAB Dollar index was very similar for animals with high or low parasite resistance EBVs which gives an early indication you can select for parasite resistance without compromising progress with production traits,” he said.

The two-year trial involved about 2,400 Angus cattle from eight herds, all with strong genetic links to Te Mania Stud at Mortlake in western Victoria.

“Genetic linkage was achieved through the use of common sires across the participating herds through artificial insemination with frozen semen,” Dr Honey said.

“All sires were recorded with BREEDPLAN and the genetic linkage provided half-sibling sire lines across a range of climatic and management situations.”

Lots of worms from few calves

FECs were recorded from weaners aged from 6–17 months, when they are most susceptible to parasites. All animals had either never been drenched or not drenched for at least six weeks prior to sampling so there was no effect from any residual chemical. The sires of each weaner were recorded and, although the dam’s details were known for each individual, their maternal contribution was ignored.

“The data showed the offspring of different sires contributed unevenly to the total pasture contamination load. For example, in a sampling from one of the herds one bull had sired 22 per cent of the calves but those calves only produced 4% of the pasture contamination,” Dr Honey said.

“In practical terms, there may only be a small number of calves in a herd that are creating the worm problem.”

Gender worm link

Another interesting outcome of Dr Honey’s work was the clear relationship between sex and worm burden. He found that bulls had significantly higher worm counts than steers, which in turn had significantly higher counts than heifers.

“It is likely that hormonal effects are expressed on the immune system but clearly there is a relationship that warrants further investigation. The finding has implications in how seedstock herds manage their unmarked calves,” he said. With Dr Honey’s research now complete, he said the challenge now lies with industry to adopt and refine the science.

“Following the project, the Angus breed now has 77 sires with a parasite resistance EBV so it is possible to select resistant lines of cattle within commercially acceptable timeframes,” he said.

“It will really depend on the seedstock industry deciding whether or not there is a demand for this EBV and whether they are satisfied it’s useful.”

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