Parasitology

All livestock grazing pastures in New Zealand have parasitic worms (nematodes) living in their intestinal tract. If unmanaged, these build up in numbers causing reduced growth, ill health and potentially even death. For decades farmers have relied heavily on chemical drenches to control parasites, but this focus on a single strategy has led to the emergence of worm populations resistant to these chemicals. Today, drench resistance is a major issue for many farmers, causing significant losses, and in some cases, necessitating changes to the whole farming operation.

Identifying parasites is often difficult: to see the adults, the host animal has to be killed, and the gut examined, while identification of eggs or larvae microscopically is often difficult, imprecise, and time consuming.  

Advancing parasite identification with DNA technology

AgResearch scientist Dr. Alex Chambers implemented and validated a DNA-based method to New Zealand, improving the identification of nematode larvae to the species level.

Traditional microscope-based methods usually only analyse up to 100 larvae at a time, whereas this advanced DNA approach can process thousands of larvae from hundreds of samples simultaneously: delivering faster, accurate, more cost-effective results.

We’ve integrated this method into our research, enhancing existing tools like the faecal egg count reduction test (FECRT), improving the accuracy of drench resistance estimates on farms. Additionally, this technology expands our understanding of parasite seasonality across farms and different livestock classes, helping to drive better parasite management strategies.

While chemicals can be applied to animals for parasite control, resistance has become a major issue. Even with chemical use, parasites can still be a problem. Breeding animals with the capacity to suppress worms in their gut is one way to deal with the problem. Breeding resistant sheep has been possible for many years and has been shown to result in fewer chemical treatments being necessary.  

AgResearch's development of the CARLA® saliva test is a powerful breeding tool. The CARLA® saliva test is a commercial service that assists in breeding for better parasite resistance in sheep, deer, and goat herds.   

Carbohydrate larval parasite antigen (CarLa) can be found on the surface of all infective nematode larvae and is released after the larvae have begun to grow after being eaten by a grazing animal. The animal's immune system can produce antibodies against CarLa that prevent the larval stage from establishing in the host, this can be measured in saliva. 

AgResearch’s CARLA® saliva test provides an accurate and simple way to select animals that suffer less from the effects of parasitic worms, and which pass fewer worm eggs onto pasture. The test measures antibodies against worm larvae in saliva; animals with high levels of antibodies are better at preventing worms from establishing in the gut. This means animals can put more of their energy into growing – without any increase in dags. 

CARLA® saliva test can be purchased and delivered to your farm gate, whereby farmers undertake swab tests themselves, sending all samples back with a short turnaround time to be provided with comprehensive results.

Worm resistance to drenches has become a serious issue for many farmers across the country – mostly in sheep and goats but increasingly in cattle. For many farmers today, and certain to be more so in the future, previous reliance on drench to manage worms simply won’t work – new approaches to managing parasites are needed. Already we have been able to tell farmers exactly what species of worms are resistant to drenches on their farm which can help with planning their future parasite management.