30 April 2011

3 minute read

There is a potential benefit that can be achieved from including genomic information in selection programmes in beef cattle. And this benefit is highest when selecting younger sires compared to older sires.

Just one of the findings of Carol-Anne Duthie and her team at the Scottish Agricultural College. Their work outlined the importance of the training population size and the effective population size as these constrain the potential benefit that can be achieved.

“Genomic selection is expected to be of particular benefit for traits that have low heritability and are difficult to measure or are only available late in the animals life or are sex limited,” she told delegates at the 2010 British Society of Animal Science’s annual conference, held at Queen’s University, Belfast.

“Therefore, genomic selection may facilitate the inclusion of further traits, such as residual feed intake, in breeding programmes which are important to the efficiency of beef cattle.”

Genomic selection (GS) utilises information about the association of large numbers of single nucleotide polymorphism (SNP) markers located throughout the genome with phenotypic information such as growth rate. This has become feasible due to the availability of large numbers of SNP markers and the development of the bovine SNP chip.

“And the aim of our study was to investigate the benefits of applying genomic selection to the terminal sire index of beef cattle considering training population size and different breeding structures,” explained Dr Duthie.

Selection index theory was applied to investigate the response of the beef terminal sire index under conventional selection or GS given the structure of the UK beef industry. Breeding objectives of the terminal sire index incorporate carcass weight, carcass fat score, carcass conformation score, gestation length and calving difficulty.

Currently recorded traits include birth weight, weight at 200 and 400 days, muscle score, muscle and fat depth, gestation length and calving difficulty. Parameters were obtained from UK beef genetic evaluations and information for the breeding goal traits were obtained from Amer et al. (1998). Selection strategies were derived from the structure of the beef industry, which was calculated from UK beef genetic evaluations data.

The effect of different breeding structures was investigated. This included selection based on young sires, where no progeny information is available, and selection based on older sires. Genomic information was included in the selection index model and accuracies of genomic estimated breeding values (GEBVs) are predicted based on trait heritability, number of phenotyped animals in the training population, the number of quantitative trait loci (QTL) underlying the trait and the effective population size (Ne).

“We found that, under conventional selection, the economic response is similar between the two breeding structures, however the slightly higher response (5 per cent) when selecting older sires is due to higher accuracy of breeding values due to the availability of phenotypic records on more relatives,” said Dr Duthie.

“Including genomic information increases the economic response to selection in both breeding structures, however the magnitude of the response in comparison to no GS is higher when selecting younger sires (up to 33 per cent increase) in comparison to the industry average (up to 21 per cent increase) where selection is based on approximately 40 per cent young sires, with a generation interval of less than three, and 60 per cent of older sires.”

She added that the size of the training population influences the economic response that can be achieved when including genomic information, where the highest response is achieved with a training population of 5,000. “However, this is constrained by the breeding programme structure and Ne. Larger training population sizes had more impact when younger sires were selected. Furthermore, the rate of economic response was higher for Ne of 100 than 500.”

Presented to the British Society of Animal Science Annual Conference, April 12 to 14, 2010, Queen’s University, Belfast. Full details: Duthie C, Sawalha R, Navajas E, Roehe R and Roughsedge T: “Economic response that can be achieved from including genomic information to the terminal sire index of beef cattle.”