Research: Solid potential to select for parasite resistence

Jon Condon, 09/10/2012

Recently completed research has demonstrated that the tools are available to select for cattle with greater resistance to internal parasites, without compromising other commercially significant traits.

Over the past 12 months, a research project led by Dr Peter Honey from Charles Sturt University has focussed on demonstrating that parasite resistance in cattle herds can be established and maintained through genetic selection without compromising enterprise profitability.

Current methods of internal parasite control rely heavily on the strategic use of chemicals. However the useful life of many products is shortened by the development of resistance by the targeted parasites, and failure of the chemicals is common.

In addition, there is growing pressure on cattlemen to reduce costs while remaining open to increasing scrutiny and traceability regarding safe, residue-free food. There is also an increasing interest in ‘natural’ and ‘organic’ food production with greater emphasis on chemical-free or low chemical production methods.

The recently-completed project focussed on resistance to internal parasites in pasture-based breeding herds in southeastern Australia.

Using faecal egg counts (FEC) from groups of weaners by different sires as a phenotypic indicator of internal parasite resistance, the research showed it was possible to develop EBVs for parasite resistance for sires.

It is already known that only a relatively small number of calves account for a large proportion of the FEC pasture contamination that occurs. The likelihood of certain sires producing calves that cause high parasite transmission has been found to be up to 20 times more than for other sires.

The heritability of this trait was found to be 37 percent (meaning that 37pc of the total variation in faecal egg output within weaner groups was due to genetic factors alone) – providing ample opportunity for selection of more resistant cattle.


Selection does not compromise other traits

Mean Longfed/CAAB $Indexes for highest and lowest 10pc parasite resistance, showing negligible impactImportantly, through the use of Breedplan and link sires, provides genetic linkages and large half-sibling sire groups from herds over a wide range of environments and management situations, the Angus Long Fed/CAAB $ Index was very similar for animals with high or low parasite resistance EBVs.

This indicates that progress could be made in selection for parasite resistance without compromising progress with other important production traits.

The research study has developed preliminary Breedplan EBVs for internal parasite resistance for 77 Angus bulls across southern Australia. Breedplan also offers the ability to monitor developments in enhanced resistance to parasites alongside continuing genetic gains in other the production traits.

The benefits to industry from adopting the technology include:

  • Increased usage of genetic selection, via sire EBVs, for enhanced parasite resistance within breeds.
  • Decreased reliance on chemical control of internal parasites.
  • Improved productivity and profitability of beef enterprises.
  • Improvements in aspects of animal welfare and environmental stewardship.

Initial benefits are likely to be to progressive seedstock producers who adopt the technology to obtain a marketing advantage over their competitors, the report concluded.

There was currently no emphasis given to parasite resistance in the selection of commercial seedstock animals, and the fact that cattle can be bred for enhanced resistance to worms had not yet been widely promoted to the commercial seedstock sector.

The gathering of faecal egg counts is not easy or convenient, meaning future research on seedstock herds with wide commercial acceptance would provide the maximum industry benefit, researchers concluded. Benefits would be transferred to those clients using EBVs in their selection decisions.

Future research progress would preferably involve collecting data from Breedplan-measured herds using link sires selected by the Australian Genetics and Breeding Unit at New England University, the report suggested.

Prospect for marker-assisted EBVs

From these herds, sires could be identified for commercial industry and to be used in breeding trials to establish populations of cattle for genomic studies. Development of marker-assisted EBVs for enhanced parasite resistance would serve as a realistic objective of future research on this hard-to-measure trait, the project’s final report said.

Development of gene marker assisted selection would greatly speed up the genetic improvement for parasite resistance. Once genomic maps for beef cattle are more refined, identification of genes controlling resistance would offer a wider option for disease control.

The identification and removal of parasite susceptible strains of cattle from a cow/calf operation would not only include the benefit of greatly reducing disease transmission and costs involved in parasite control, but deliver environmental benefits stemming from reduced chemical use on-farm; reduced cattle handling; and potential to deliver consumer benefits associated with lower chemical use and better animal welfare outcomes.

  • • The final report, ‘A Genetic Approach to Internal Parasite Control in Australian Cattle,’ can be viewed here




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