Good Horsemanship

Hybrid Vigor

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We've talked about hybrid vigor before, and the importance in bringing in some diversity.

This could be beneficial in helping to breed spavin out of the breed; put better bone on the horses, or even strengthen gaitedness.

"Hybrid vigor or increase in size, yield, and performance found in hybrids, especially if the parents have previously been inbred. The application of heterosis has been one of the most important contributions of genetics to scientific agriculture in providing hybrid corn, and vigorous, high-yielding hybrids in other plants and in livestock."


[] Heterosis occurs when unrelated strains or breeds are crossed.

[] Heterosis is the recovery of performance depressed by inbreeding in the parent populations.

[] The degree of heterosis for the same trait varies between strains, breeds and environments.

[] A hybrid dam improves her offsprings' chance of conception and survival through maternal heterosis. This individual's own hybrid status improves its growth through offspring heterosis.

[] Heterosis is highest for low heritability traits of reproduction and survival but lowest for high heritability traits of post-weaning growth and carcass fatness.

[] The performance of a crossbred can be predicted knowing the average performance and degree of heterosis of the breeds crossed.

The members of the same population (eg. breed or strain) are usually related and therefore somewhat inbred. When two different populations are crossed, the level of inbreeding in the offspring falls to zero and there is an improvement in those traits which suffered from inbreeding depression in the parent populations. This improvement is heterosis.

As with inbreeding depression, heterosis is most often seen in low heritability traits, eg. those connected with reproduction, early growth and survival. It occurs least often in high heritability traits, eg. carcase characters. Heterosis is usually greater if the genetic difference between the crossed populations is wide. Thus the crossing of breeds should give more hybrid vigour than the crossing of strains within the same breed.

By Elaine Reynolds:

Inbreeding increases homozygosity. Breeders commonly use inbreeding to set type"; this means that they will mate animals that are related and share desirable characteristics, so that those characteristics will become homozygous, and all offspring of the inbred animal will inherit the genes for those characteristics.



There are two theories of hybrid vigor, or heterosis. These theories are not mutually exclusive and both contribute to the incresed health of individuals that have a high degree of heterozygosity.


From this theory we have developed ways to inbreed, discover the genes that are undesirable in the line and eliminate them from the genepool, theoretically ending up with a purged genepool and healthier dog. As long as the undesirable traits that we are removing are easily identified in the pups and we can cull them before they are placed, this works fairly well, too, for a time.



The genes that control the immune system pass down through generations as "haplotypes" These are groups of alleles that lie closely together on a chromosome and are seldom separated by crossing over during the formation of gametes.




Reducing the diversity in the genepool proportionatly increases the chances for an individual to inherit identical haplotypes from each parent. The result is tremendous suffering.

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