Ovita AgResearch CARLA Saliva testing

Summary

The primary objective of this project was to assess the applicability of the CARLA Saliva test as an alternative to faecal worm egg counts for making young sire selections in Australian sheep breeds across different climatic zones. Parasitism with gastro-intestinal nematodes is a significant limitation on animal productivity. Unfortunately, the regular and sustained widespread use of a limited number of drench families to control parasites has led to the development of anthelmintic resistance.  In Australia especially, failure of anthelmintics is widespread.  The challenge for researchers is to develop new technologies for parasite control that are effective, sustainable, have little if any impact on productivity and are farmer friendly.
The CARLA Saliva test measures levels of IgA antibody in saliva to the nematode L3-specific surface molecule known as CarLA (carbohydrate larval antigen). IgA levels in saliva were measured on a regular basis in 8 Information Nucleus Flocks (INF) located across Australia. Using the information obtained, we were able to follow the development of this protective immune response to nematode parasite challenge in young lambs after weaning and could also assess seasonal changes in parasite larval challenge faced by the flocks at each of the different sites.
​The CARLA responses between and within flocks varied widely.  Based on the responses in young lambs and Sentinels, some flocks appeared to have good larval challenge present all year round, e.g. Kirby, Cowra, Rutherglen and probably Katanning.  Other sites had low CARLA responses for most of the year e.g. Trangie, Straun and Turretfield.  At these sites CARLA responses and thus larval challenge appeared to be at their highest levels in June and September.   In young lambs post weaning it took 3-4 months of exposure to larval challenge before CARLA responses matched that of co-grazing Sentinel animals. This is similar to the length of time it takes for the CARLA response to develop in lambs in New Zealand sheep breeds.   Potentially the CARLA saliva test may be of benefit in place of WEC (worm egg counts) testing in Australia as it would allow testing for a parasite resistance trait while also applying drench treatments for controlling parasites, breech soiling etc.   All CARLA data has been provided to the Sheep CRC for detailed analysis. The results from this will be reported by the Sheep CRC. WEC data was provided to us from Kirby.  The WEC CARLA correlation was very encouraging at this site.