The new breeding program, designed to get the best out of the animals, is the first major advance in classical breeding in 20 years, said William Muir of the Purdue Department of Animal Sciences. By picking less aggressive individual animals from a broad range of families, the same breeding program can be used for hundreds of generations.
The new program enables breeders to have optimal improvement in productivity while minimizing the health risks associated with inbreeding, he said. At the same time, the program overcomes competition among animals for resources that often means less aggressive animals suffer from lack of nutrition and increased injury. In a group composed of both aggressive and passive animals, even those at the top of the pecking order are harmed from overeating, which wastes food because their bodies can't properly utilize the nutrition.
"Genes not only control your own behavior but also impact others," Muir said. "For instance, if my genes make me more competitive and aggressive, it almost always comes at the expense of someone else. If a pig or chicken rises to the top of the ladder by stepping on the shoulders, or heads, of others, then a breeding program doesn't make progress."
Muir, who previously researched and advocated a group-selection theory to obtain a kinder, gentler bird, refines this breeding approach in a study published in the current issue of the journal Genetics. In Muir's new plan, individuals are chosen for their passiveness based on equations that identify whether an animal is so aggressive that it will negatively affect its penmates' health and productivity.
In the original group-selection program, families of animals that produced less aggressive animals were kept to
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