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Mixing it up can yield breeding advantages

The science behind hybrid vigour has been known for a long time, but producers are encouraged to tap into its potential.
Crossbreeding can help overcome inbreeding depression that occurs in purebred or straightbred populations.

WESTERN PRODUCER — Crossbred cattle have known advantages over purebreds due to hybrid vigour.

Dr. Reynold Bergen, science director at the Beef Cattle Research Council, says hybrid vigour, also called heterosis, is the degree to which progeny outperform the average of the two parents.

“If breed A averages 100 and breed 2 averages 110 for a certain trait, the calf’s expected performance would be the average between the two (105). But if the calf’s performance is 112, it outperformed the parental average. That is hybrid vigour.”

A calf from that cross might average 108, which is still greater than 105, but breed 2 would be the better choice for that trait. That means hybrid vigour isn’t as helpful for a certain trait when one breed vastly exceeds the other in that trait.

“That’s why dairy cattle are usually straightbred Holstein. Their milk production is so phenomenal that crossing with an Ayrshire will never exceed the parental average, and most dairy producers are willing to sacrifice longevity or fertility for production,” says Bergen.

“But if producers want to improve longevity or fertility and are willing to accept lower milk production, crossing with a dairy type Simmental (as an example) is a good way to go.”

One of the first crossbreeding studies in Canada took place in the 1930s. In 1938, Grant McEwan, an animal science professor at the University of Saskatchewan, and A.M. Shaw published An Experiment in Beef Production in Western Canada, which summarized their four-year crossbreeding project with Angus, Shorthorn, Galloway and Hereford. Each calf crop had 25 percent straightbred and 75 percent F1 crossbred calves. The crossbreds averaged three percent higher weaning weights, average daily gain and finished weights than the straightbreds, and 18 percent more crossbred calves had top carcass grades.

Crossbreeding overcomes inbreeding depression that occurs in purebred or straightbred populations.

“Cattle of the same breed all belong to the same family tree. Cattle from distant branches of the pedigree are less related than those from nearby branches, but are still related to some extent,” says Bergen.

Every animal in its species has the same genes, but with variations. Some genes mask other genes. The polled gene can hide the horned gene. Some genes are dominant and some are recessive.

For instance, black is dominant and red is recessive. A cow is red if it inherits a red gene from each parent. Two black animals that carry a red gene can produce a red calf, but two red animals cannot produce a black calf since neither has the dominant gene for black.

Sometimes a hidden gene can be detrimental. Two animals might carry a recessive gene for dwarfism or other genetic defect, and it shows up in offspring if that recessive gene is doubled up.

“Genes get passed from one generation to the next, and if individuals are closely related there is more chance for doubling up recessive genes,” Bergen says. “A breed is one big extended family. Purebred cattle are related to each other.”

All breeds were originally created with some degree of inbreeding/linebreeding to standardize desired traits in foundation animals. A breed is a closed group to maximize uniformity and exclude unwanted traits.

Keeping a breed “pure” limits genetic potential and tends to accumulate inbreeding over time. This leads to less hardiness, immune response and vigour.

Crossbreeding is the opposite of inbreeding and opens the door for wider genetic variation. Heterosis is essentially the recovery of lost potential; a reversal of accumulated inbreeding depression of traits. In just one generation, crossbred offspring exhibit the greatest degree of what was lost through many generations of pure breeding within a closed gene pool.

Calving ease, growth rate, weight, carcass yield and quality are highly heritable.

“It’s like piling bricks; you can keep stacking more good genes and building those traits higher and stronger,” says Bergen.

“When you select for big growthy, well-muscled calves, however, you get those traits but the fertility and longevity of those cattle go down. It’s like they are on opposite sides of a teeter-totter.

“Traits like fertility, longevity and strong immune systems are very hard to select for, partly because they depend on combinations of genes. They are not so much a stack of genes as a web of genes,” he explains.

“The way you improve those traits and strengthen that web is to shake up the genes and add more variation, by crossbreeding, to get the best of both worlds. The highly heritable stacked traits from one breed work just fine with the tall stack of bricks from the other breed, but the different combinations add back the fertility, longevity, immunity, etc. The genes from one breed combined with the genes from the second breed produce a much stronger set of genes for those traits.”

Hybrid vigour is often seen in calves showing better disease resistance, growth and performance. Crossbred females tend to be more fertile and last longer in the herd, weaning more pounds of calf in a lifetime.

“You might get three or four percent hybrid vigour for calf performance with a crossbred calf, but you’ll get 15 percent hybrid vigour for longevity with a crossbred cow and all the extra calves she’ll produce,” says Bergen.

“The difference between eight years in the herd compared to 12 years or more, since many crossbred cows produce well into their teens, adds up.

“The more genetically different the breeds are, the more hybrid vigour you get. If you cross a Red Angus to a Black Angus, you won’t get much because those breeds are closely related.

“When you cross Hereford with Angus you get much more, and even more if you cross a British breed with a European breed, since they are even less related,” he says.

“In 1950, Agriculture Canada researchers mated Brahman bulls to Hereford cows at the Onefour research station in Alberta, then compared lifetime productivity of 22 Brahman x Hereford F1 females to 26 straight bred Hereford females. Sixteen years later, all but five of the 26 straight breds had been culled for failing to wean a calf in two consecutive years, for cancer eye, or udder structure. In contrast, 13 of the original 22 crossbreds were still in the herd,” says Bergen.

“Many herds in Canada and the U.S. were crossbred in the 1980s but most folks have been using Angus bulls and now many herds are almost straight Angus. Angus are good cattle but there are some big benefits in shaking up the genetics.”

A project led by Dr. John Basarab of Alberta Agriculture used DNA tests for breed composition.

“Among other findings, this study found that cows with higher genetic diversity averaged $161 greater net annual returns than less genetically diverse cows due to $74 higher income per weaned calf and $88 per head lower replacement costs.

“Hybrid vigour is an opportunity for commercial producers to improve cow fertility, longevity, lifetime productivity and production economics,” Bergen says. “Crossbreeding is how you get that, and it’s free.”

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