Natural immunity is best defence against parasites

More than 8,000 CARLA saliva tests have been carried out for sheep breeders since the CARLA Saliva Test was introduced in October 2010.

The test identifies sheep which have protective immunity to intestinal parasites so that stud breeders can breed for improved host resistance in their animals.

Beef+Lamb New Zealand and the Ministry of Business, Innovation and Employment have jointly funded the research programme via the Ovita consortium.

AgResearch Senior Scientist Dr Richard Shaw says that the CARLA response to parasites is closely related with animal productivity.

“The better the CARLA response the more productive they are.”

“Parasitic worms in sheep are estimated to cost farmers around $300 million in lost production and treatment costs and are the number one stock health concern for farmers,” he says.

“One of the big issues for sheep farmers is parasites because of their impact on animal production and the increasing issue of anthelmintic resistance,” he says.  “With the CARLA saliva test breeders can select for improved parasite immunity and breed it into their stud animals.”

The test identifies the level of a particular antibody (IgA) in sheep which binds to the CARLA molecule present on the L3 stage of intestinal parasites before they mature in the sheep gut.  This antibody binding prevents L3 larvae from establishing and thus being able to mature into adult parasites. This breaks the parasite’s life cycle at the infective stage and means that energy that would otherwise be used to fight adult parasites can be used by the animals for growth.

The heritability of the antibody response is moderately high at around 30%.

Scientists say that because sheep farmers have tended to rely on drenching to control parasites and have not previously selected for resistant animals, resistance levels to parasites are low.

The CARLA Saliva test is also being trialled in Australia and Scotland to validate its use for breeding selection in different environments.

In New Zealand further research has been continuing to determine the effectiveness of the test on the saliva of other ruminants.