Bigger is usually better where litter size is concerned. Scientists with USDA’s Agricultural Research Service’s U.S. Meat Animal Research Center in Clay Center, Neb., have identified a genetic marker that could help swine breeders select animals for increased uterine capacity and litter size. This genetic discovery could give swine breeding an efficiency boost.

How does it work? Research leader Jeffrey Vallet and his colleagues discovered a single nucleotide polymorphism, or SNP, in the erythropoietin receptor gene. The hormone erythropoietin binds to this gene and stimulates production of red blood cells.

SNPs are genetic variations that provide information about an animal’s genetic value and can be used in breeding programs. In studies on two unrelated swine populations, the scientists showed that this newly discovered SNP is associated with increased litter size.

The SNP creates either a T or a C allele — an alternative form of a gene that controls traits such as hair or eye color in humans.  In swine, sows with the T allele have an average litter size that is one or two piglets greater than for sows with the C allele, the study found.

The T allele occurred at low frequency in the population that was studied, but it’s still a beneficial genetic difference. So how can it be used?

Vallet and geneticist Bradley Freking have developed an assay to detect the SNP in individual sows. It will provide the ability to quickly identify the beneficial SNP allele, which eventually will let breeders select sows with improved uterine capacity and litter size, thus increasing production efficiency.