Mating decisions made in commercial cow-calf operations determine if (and how much) Gene Combination Value (GCV) we create in the next generation.
In the genetic model: Phenotype = Genotype + Environment. Genotype represents the genetic potential of an animal to reach a level of performance and can be split into two components. The component of Breeding Value (additive genetic merit) was covered last week. The focus of this article is GCV which can also be thought of as the non-additive part. GCV is based on the effect of gene pairs at loci across the genome. It is part of the animal’s genotypic value and impacts the animal’s performance potential; however, since it is based on gene pairs, it can’t be transmitted from parent to offspring. In commercial cow-calf operations we can create GCV through mating decisions. The decision to crossbreed is a mating decision.
Crossbreeding provides commercial cattlemen the opportunity to combine desirable characteristics of two or more breeds (breed complementarity) and increase performance due to hybrid vigor (heterosis). Hybrid vigor is the result of GCV.
For example, if we make the mating decision to use a Charolais bull on our Angus cows, we are creating F1 black-nosed smoke calves with 100% level of individual heterosis. Why? Because the F1 generation will have a Charolais gene paired with an Angus gene across all loci.
Hybrid vigor is the superiority in the level of crossbred offspring’s performance over the average level of the purebred parents involved in the cross. In scientific literature, levels of heterosis are typically expressed as a percentage as shown in the example below:
A Charolais bull with the additive genetic potential for 660 pounds of weaning weight is crossed with a herd of Angus cows with the additive genetic potential for 640 pounds of weaning weight. The resulting F1 crossbred calves weigh 683 pounds at weaning.
– Average of the purebred parents is 650
– The 683 pound weaning weight of calves is 33 pounds more than average of the parents
– (33/650) x 100 = 5% level of heterosis from this cross.
The 5% level of heterosis is not additive, it is the result of the biological phenomenon of hybrid vigor created by crossbreeding resulting in a GCV that is non-additive.
It is noteworthy that if the F1 heifers and bulls resulting from this cross were mated, or if we began a two breed rotation involving an Angus bull mated to the F1 females from this cross, we would lose hybrid vigor (GCV) in the resulting F2 calf crop. Why? Because not all loci would have a Charolais gene paired with an Angus gene. Hence, GCV (based on gene pairs) is NOT transmittable from parents to offspring. It must be created through mating decisions. Thereby, purebred animals are an essential component for effective crossbreeding programs.
Final Thoughts for Building GCV
Each selection and mating decision should be intentional, deliberate and made for a purpose. Selection decisions impact BV. Mating decisions impact GCV. Choose breeds (and breeding stock within those breeds) with high breeding value for traits of economic importance to your operation. Crossbreeding (to increase GCV/hybrid vigor) does not replace additive genetic merit, it builds off of it. Finally, more breeds introduced into a crossbreeding program will result in more heterosis but also increase variation. Performance levels of some traits are influenced more by additive genetic merit, other traits benefit more GCV. More on that topic next week.
