A few years ago, I sat in on a dairy conference where farmers talked about their experiences after adopting new technologies. One farmer had fairly recently assumed responsibility for the family farm. His family had focused on breeding cows for the show ring but he had decided that he wanted to focus on production instead. He considered that the best way to do that was to concentrate on selecting sires based on genomics.
He was cautious about not decreasing the genetics of his herd by increasing inbreeding. He hoped to avoid that by purchasing only a limited amount of semen from each set of new genomic bulls but admitted that he had a challenge in figuring out how closely related individual bulls actually were. He relied on the inbreeding co-efficient provided by the genetics companies. These are largely (if not exclusively) based on pedigree information.
Pedigree analysis provides a useful indication of the genetic diversity but it will likely be possible to use genomic information to estimate the true genetic relatedness of cattle. This would be a valuable tool to reduce the risk of losing genetic diversity.
Using genomic information to assess inbreeding could be complex. Genomic information may need to be collected over the entire genome but detailed genomic data over small areas of the genome will also be needed. This is to avoid inadvertent loss of genetic diversity of small but important sections of the genome. Even when there is enough information to estimate the impact of election of bulls on larger populations, it may still be difficult to assemble data to make appropriate selections within individual herds.
The search for new ways to limit the impact of inbreeding will continue because inbreeding has a significant impact on dairy production. Like with other technologies, we will learn to manage both the benefits and downsides.
As more phenotype information is accumulated, it has become increasingly likely that bulls can be selected to consider an even wider range of traits. One area that many veterinarians look at with expectation is the consideration of health traits. A drawback has been that health traits such as disease occurrence in calves have not shown very high values for heritability — that would mean that making progress through sire selection might not be easy.
With genomic evaluation, it looks as if it might be possible to make better progress. One way to make progress easier, no matter what the selection process, would be to have a better set of health data for calves. The reliability of any association between genomic traits and health would be improved if it were likely that the data on calf health was more uniform and reliable. A recent research report from the U.S. tried to do just that.
In the study, they collected data on pneumonia and scours, the two most common diseases in dairy calves. They also collected data on death rates, no matter what the cause of death of a calf. They related those health events to the genomic information from cattle within those herds. Using this large data set, they concluded that advancements would likely be possible but would be similar to other traits that have low heritability.
Sire selection may become another tool to help maintain calf health. The low heritability means that any benefit will still depend on the implementation of good infectious disease control practices too.
Dr. Robert Tremblay is a veterinarian for Boehringer-Ingelheim and lives near Guelph.
