While not at present a practical strategy, research indicates that there may be the potential to utilise the variation in natural worm resistance between individual cattle to assist in the management of worms.
Cattle that are resistant to roundworms will shed less eggs in their faeces and will have lower faecal worm egg counts (WEC). In breeds where this is a heritable trait this resistance can be passed on to their offspring.
Heritability of worm resistance within breeds in Australian cattle has been reported to range from 12-57%, which is similar to figures cited elsewhere in the world. Variation in heritability has also been observed in different environments and across different roundworm species.
Brahman cattle have been shown to have significantly lower WEC compared to Tropical Composite cattle. Worm heritability ranges from 40-57% have been reported with Brahman-sired calves showing a tendency for lower WEC across all roundworm species.
The measure of an individual’s genetic contribution to the inheritance of a particular trait is called its estimated breeding value (EBV).
A number of EBVs have been developed for important production traits in Australian cattle relating to weight, carcase, fertility, birth, etc., and these are recorded in the BREEDPLAN genetic database. However, WEC EBVs are not currently available on BREEDPLAN because measuring worm resistance in cattle is challenging.
Preliminary WEC EBVs were developed for 99 sires from eight Angus herds in NSW and the heritability of worm resistance was reported to be 41%. Genetic studies have found evidence to suggest that resistance trait markers are present in some cattle breeds. Research is ongoing to identify these.