BY: LYNDA GRAY

GENETIC SELECTION FOR PARASITE resistant sheep need not be at the expense of production traits.

That’s one of the key messages from Kathryn McRae, an AgResearch scientist.

The best way farmers could incorporate the benefit of this trait while pursuing chosen production goals was to select rams using the NZ maternal worth index and the additional trait of WormFEC (NZMW+F).

However, McRae, who has a special interest in the genetics underpinning disease resistance, says genetic selection is not a quick fix for the increasing problem of anthelmintic resistance in sheep parasites.

“The breeding of sheep with an increased ability to resist infection is one tool. It’s a permanent tool, but it takes generations of breeding for the benefits to accrue.”

Presenting at the New Zealand Veterinary Association conference in June she summarised the key findings of research over the last 25 years about breeding for internal parasite resistance in sheep.

One of the projects had dispelled the popular view that parasite-resistant sheep had more dags than non-resistant sheep.

The 2012 project by a PhD student involving a comparative analysis of 45,000 dag records and 130,000 FEC records showed a very low correlation between parasite resistance and dagginess. That meant selection according to a low dag score was not at the expense of parasite resistance, McRae said.

“Dags, or lack of them is a heritable trait and something that ram breeders could be recording to make genetic progress. They’re easy and free to measure.”

Research had also proved that resistance to internal parasites was geographically transferable.

“While some may believe it’s better to select and use rams within a specific environment or geographical region, that’s not the case with parasite resistance.”

The next 25 years of research would likely include DNA identification of larvae species from faecal samples.

“If we can look at the breakdown of species within faecal egg counts, it may provide additional information that could help in the breeding of more resistant sheep.”

Another likely project was to identify the typical behaviours of sheep whose health is compromised through parasite infection. The measurement of the time a sheep spent moving, resting, or ruminating with devices such as GPS collars and accelerometers would help with gathering this information.

“That type of research is already happening in the dairy industry and we’re hoping that as the technology advances and gets cheaper we’ll be able to adapt it for the sheep industry.”

The microbiome – DNA markers of microorganisms – within a faecal or rumen sample was another new and future arm of research that could provide more insight about the interaction between sheep and the parasites responsible for infection.