Is Holstein genetic diversity at risk?

World Holstein Conference | Large gene pool lowers risk, genomic selection increases it

TORONTO — Holsteins trace back to a small number of key ancestors, which has some within the dairy industry concerned about inbreeding and loss of genetic diversity.

This risk was discussed at the World Holstein Conference held in Toronto Nov. 6-7.

Bulls with names like Starbuck and Blackstar were pivotal breed influencers in North America and Australia.

As the science of genomics advances, there is a chance breeders will select only the elite animals and create future problems. However, studying the genetics of thousands of bulls shows there is a large gene pool.

“One of the astonishing things when you do that is how much genetic variation still exists in our cattle,” said Ben Hayes, head of the Dairy Futures Co-operative Research Centre in Australia.

The organization is working with other countries on the “1,000 bulls genome project,” which is sequencing the DNA of key ancestors within purebred cattle breeds.

Eight groups are involved in the project, which has sequenced 236 bulls and two cows, including 130 Holstein, 48 Angus, 15 Jersey and 42 Fleckvieh.

Genomic information has allowed dairy cattle to achieve greater rates of genetic improvement in a shorter period of time, but it could also be associated with higher rates of inbreeding, said researcher Flavio Schenkel of the University of Guelph.

Studies at Guelph showed a clear reduction in genetic variance among Holsteins from 1950 to 2006.

Genomic selection started in 2009 following the release of the bovine genome in 2007.

“Genomic selection is expected to increase the loss of genetic variation due to inbreeding,” Schenkel said.

Inbreeding, in which close relatives are mated, can cause a decrease in performance, lower milk production and reduced fitness of the animals as well as possible genetic defects.

Breeders need to blend pedigree and genomic information to study the effects of inbreeding and find ways to control it, said Schenkel.

Artificial insemination companies also see a risk of inbreeding, said Marjorie Faust, senior research director of the genetics company ABS Global.

Fewer sire families are appearing in pedigrees, which happened more often in the early stages of genomic adoption. However, it appears that more outcrosses are now being made rather than overusing the genetics of popular cattle.

“It remains to be seen if this is a true trend or whether it is just a reflection of the sire candidate population because we tend to see a lot of cyclicity, depending who the elite sires are,” she said.

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