Heterosis is defined as the performance superiority of crossbred progeny over the average of its parents
North American beef herds lack hybrid vigour and that directly affects every calf crop.
“Looking around the country there is a very high proportion of straight breeding going on,” said Alison Van Eenennaam, extension genomics specialist of the University of California, Davis.
“From a genetics perspective, when I look at the competing protein industries like poultry or swine there is a very good understanding of the value of heterosis, or crossbreeding. It should always be a consideration for commercial cow-calf production,” she said in a recent webinar on using genomic selection tools.
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Heterosis is defined as the performance superiority of the crossbred progeny over the average of its parents. Heterosis improves general health and resilience as well as milk yield, cow longevity and weaning weights.
These are the main profit drivers for a commercial operation. The general rule of thumb is not to have females with more than 75 percent of one breed, she said.
Beef magazine conducted a recent producer survey and found more than 70 percent of herds in the United States are mostly British based with a high percentage being Angus.
The trend toward black cattle among commercial herds is common but producers need to think about crossbreeding for overall improvement, Van Eenennaam said.
Breed associations have or are working to develop expected progeny differences for fertility. It is important to have this information for reproductive longevity because it is a profit driver for self-replacing herds.
“If you keep replacement females there is no single trait that is going to be more economically relevant than reproductive longevity of females. You can think about cow depreciation costs as a reason why,” said Matt Spangler of the University of Nebraska.
Canada faces a similar situation, said John Basarab of the University of Alberta and Alberta Agriculture.
Audits going back 30 years show a decline in crossbreeding programs where two or three breeds were used.
“More recently there is a real predominance of red and black within the western Canadian population,” he said.
Cow-calf producers need to look after herd fertility, then growth followed by carcass traits.
“For the cow-calf producer we follow a two to one rule of thumb. Fertility traits from a sustainability-profit point of view are 10 times more important than carcass traits and two times more important than growth traits,” he said.
“That principle has stood the test of time,” he said.
The greater the hybrid vigour in a cowherd, the longer each female stays in the herd. That also affects profit, sustainability and the carbon footprint of a herd.
Crossbreeding studies done in Canada and the United States also show a general influence on health. Feedlot calves with a good level of heterosis are healthier.
Tools like genomics contribute to this knowledge.
Basarab was part of a partnership with the federal and provincial governments and University of Alberta that developed a genomic tool to measure hybrid vigour. Marketed through Neogen Canada, it is sold as EnVigour HX and in recent months it has been sold in Canada, U.S., Brazil, China, Scotland and Australia.
Producers take a sample of DNA from blood or hair and it is analyzed in a laboratory. The results provide a hybrid vigour score based on a large reference database of genotypes and full sequences to characterize the different alleles that different breeds carry.
Comparing the DNA sample against that database produces a breed composition. A formula is then used to calculate heterosis and produce a score.
“Heterosis works really well when you deal with low heritabilities. It is less effective when you are dealing with high to moderate heritabilities like growth rate and carcass traits,”Basarab said.
Hybrid vigour needs to be established each year with crossbreeding.
Commercial cattle producers have been enlisted to monitor the amount of hybrid vigour within their herds over time.
Some herds were good with above 50 percent hybrid vigour but others had a wide range of scores from 10 percent, meaning it is almost purebred, to 70 percent indicating it is highly crossbred. Results like that within a single herd create too much variability.
“Within the same mating group you had everywhere from low hybrid vigour to high hybrid vigour, which means from a breeding point of view that would have been very difficult to manage,” he said.
Producers should document the breed composition of their cows and manage them as a breeding group to help decide which breed of bull to use with them.
For those using crossbred bulls, it is also important to know their composition so mating decisions with breeding groups of cows can promote hybrid vigour.
DNA testing comes with a cost, so Basarab recommends testing replacement heifers so more strategic breeding decisions can be made.
“That would give you an idea which of those heifers you would want to keep for maternal heifers,” he said.
