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Separating stature from major Holstein traits

A new composite index should help maintain desirable traits, while de-emphasizing stature

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Canada’s dairy breeding sector is attempting to slow a gradual increase in the average size of the nation’s Holstein.

At Lactanet Canada’s recent Open Industry Session held in Guelph, geneticist Dr. Allison Fleming provided information about the development of a composite index of four well-established dairy genetic traits.

Why it matters: As the average height and overall size of animals increases, producers can find themselves faced with limitations related to housing, equipment, maintenance and animal health.

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The aim is to weed out the increase in stature in Holsteins that has occurred inadvertently over the years, while producers targeted improvements in other traits.

This work, which Fleming hopes will be reflected on published Holstein bull proofs beginning in April, 2021, follows on the heels of the Holstein Canada breed association’s implementation, a little more than a year ago, of a “too-tall” defect in its scoring system for cow classification — among other changes aimed at slowing the gradual growth.

According to an article in the May-June 2019 edition of the breed association’s Info Holstein magazine, the average height of a Canadian Holstein increased by more than 2.5 centimetres over the past decade.

“Stature has become a growing concern in the industry,” the article stated, adding that the current average height of 150 to 154 cm sees Canadian producers experiencing such challenges as “animals not fitting into equipment, more prone to injury (due to not fitting properly in stalls or equipment), increased calving difficulties due to larger calf size, and ‘clumsy cow syndrome (cattle lacking a balance of parts, tall with a narrow chest)’.”

In an interview with Farmtario, Fleming said Holstein Canada’s classification changes will eventually lead to a lesser likelihood that the next generation of calves will mature to be larger than their dams.

But because breeding decisions showing the influence of the too-tall defect won’t come into effect until the current round of bulls’ daughters eventually get classified, this could take a while. It’s her hope that Lactanet’s work on a composite genetic index — taking into account the established major traits of mammary system, feet and legs, dairy strength, and rump — will translate more quickly, and more systematically, into stopping or at least slowing the growth.

The key to the work, the Lactanet geneticist says, is eliminating what has been an inadvertent selection for increased stature when farmers have aimed to enhance their offspring in terms of mammary system, feet and legs, or rump. She notes the inadvertent effect is understandable, given that stature is among the most heritable traits from generation to generation in cattle. But science indicates it doesn’t necessarily have to be so. The genes for what are seen by the dairy industry as ideal mammary system, feet and legs, and rump are separate from the genes for stature.

A composite index including these three traits has been implemented in the United States that separates out the effects of stature so bulls could score worse if they produced larger heifers that were larger than their dams, Fleming told Open Industry Session.

In Canada, the composite index being created by Fleming and her team should eventually promote genetics for ideal mammary system, feet and legs, and rump, while remaining neutral on stature.

For the fourth major trait in the Canadian classification system, dairy strength, stature is actually part of the genetic determinant for what’s seen as the ideal Holstein. So it will be impossible in the composite index to select for smaller stature while maintaining dairy strength. Fleming says the index is still in the research stage but will hopefully be implemented when Lactanet updates its Lifetime Profit Index and Pro$ rankings in April, 2021.

She reported Lactanet’s work is being done in keeping with feedback from the industry that stature is a concern. That same feedback, though, also made it clear that dairy strength is still important to Canadian Holstein breeders, and that they wanted that trait’s prominence in the classification system maintained despite its correlation with stature.

“So it’s possible that the index will still lead to very slight increase in the breed stature,” she said. But with farmers making decisions based on neutrality towards stature in the other three major traits, she believes the new composite index will help achieve what the country’s Holstein breeders are looking for.

About the author

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Stew Slater

Stew Slater operates a small dairy farm on 150 acres near St. Marys, Ont., and has been writing about rural and agricultural issues since 1999.

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