Breeding wireworm-resistant Meatmasters

Through rigorous selection, Meatmaster stud breeder Nico Grobler from North West has succeeded in significantly reducing wireworm infestation in his Kern Meatmaster flock. This has enabled him to run the stud successfully in an area highly susceptible to the parasite. Annelie Coleman reports.

Annelie Coleman

The most dominant roundworm in South Africa’s summer rainfall areas is Haemonchus contortus. Known as wireworm (haarwurm) in South Africa and barber’s pole worm elsewhere, it is a blood-sucking parasite that targets sheep and goats, and can cause substantial blood loss in affected animals. It is particularly rife from February to May.

According to Nico Grobler, who keeps a 300- head Meatmaster flock near Ventersdorp in North West, wireworm can seriously threaten the long-term sustainability of a sheep flock and is the greatest hazard to sheep farming in his area.

“My objective is eventually to eradicate all animals in the flock that need treatment for wireworm. To that effect, I only use rams that have never been dosed for wireworm,” he says.

Grobler and his team use the FAMACHA system to evaluate the animal’s anaemia level and thereby the extent of wireworm infestation and whether or not treatment is required. This is done by comparing the colour of the mucus membrane on the sheep’s lower inner eyelid with the colours on a standardised ‘eye score’ card.

TO CULL OR NOT TO CULL?

Very few of the ewes that need to be treated for the parasite are allowed to remain in Grobler’s flock, while rams needing treatment are culled without exception. The ewes are weighed and monitored monthly according to the FAMACHA system. The decision of whether or not to cull is based on the infected animal’s genetic merit and the value of the contribution she makes to the stud.

A variety of products are used to treat infected animals to prevent the development of resistance.

Grobler says he simply cannot afford any animal that threatens the health status of the flock.

“I replace 20% of the ewes annually. By continually replacing them with wireworm-resistant animals, I’m well on the way to having a flock that’s entirely unaffected by the parasite. So far this year, I’ve had to treat only about 20% of the adult ewes, despite the extremely high rainfall of 800mm.”

To illustrate the value of rigorous selection for resistance, Grobler says that 80% of the progeny of a particular ram that was dosed once contracted wireworm in 2019, although the ram fared exceptionally well in veld tests. However, only 20% of the progeny of a ram that was never dosed were affected by the parasite in 2019.

RESISTANT INDIGENOUS BREED