August 3, 2005
Happy and Passive Means More Productive Animals
WEST LAFAYETTE, Ind. -- Breaking up families can be sad, but in a new method for selecting passive livestock animals, that's a main ingredient for better long-term productivity, according to a Purdue University geneticist.
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 together. The unfortunate side effect is that such inbreeding can have dangerous genetic consequences, meaning the program could only be used for only a few generations. Muir's new breeding plan avoids the problems of inbreeding.
Because animal well-being is an important factor in livestock breeding and because animals need to be housed in groups, not only can selecting for less aggressive animals increase productivity of individual animals, but also that of the group as a whole, Muir said. Muir calls this the associative effects of genetics.
"It's important in a group setting that the animals' genes not have a negative effect on others," Muir said. "If one pig is aggressive, his genes are negatively impacting 16 pigs. So, if we select pigs or other animals that get along together, then we can have animals that grow well."
In groups with aggressive animals that overeat, productivity of all the animals tends to decrease because the animals that eat more than required use the food less efficiently, meaning they waste food and energy.
"In terms of energy, you can waste energy by maintaining a pecking order," Muir said. "But if animals don't care about a pecking order and they get along, that energy is transferred to production. So, it's a winning situation."
Muir has worked with pig breeders to establish this type of selective program but used Japanese quail in the current study to validate the practice. He chose the birds because they tend to be very aggressive, even cannibalistic. In addition, they were a good study model because they reach maturity in about six weeks, are easily tagged and bred so pedigrees can be maintained, and it takes little room and feed to breed and raise them.
While beak trimming is used in some poultry breeding programs to minimize birds injuring each other, Muir's birds weren't beak trimmed so that their natural behavior could be observed.
"In my quail experiment, we have definite data and facts showing how the birds react in different size groups," Muir said. "We could assess how much negative impact aggressive birds were having on other birds.
"Aggressive birds were causing a weight decrease in the other birds by 25 percent compared with birds housed in non-aggressive groups."
Muir found that in just two generations of picking more passive quail, the flocks had a dramatic decrease in aggressive behavior and injuries. The study also showed that when classical breeding approaches were used, competition became worse and productivity declined, he said. The only way to solve this problem is through accounting for competition in the breeding program, as the new method does.
This breeding program is easy to implement, requiring only that computer programs be used to define competitors and set up breeding and growth groups, Muir said.
"This will enhance production traits that are influenced by associative effects while also improving animal well-being, which leads to a successful situation for producers, consumers and animals," he said.
The old adage that athletes are born and not made may be even truer of animals.
"If you're born with really, really passive genes, it will be hard for you to become nasty and aggressive," Muir said. "Animals don't have the ability to see into the future and decide that 'if I'm really aggressive, I can get ahead.'"
Muir's study also examines genetic benefits that can be obtained by using the theory to track productivity in plants. This is evident when documenting the performance of trees where larger trees and certain types of trees have competitive advantage for nutrients and sunlight.
"Researchers recognized this in tree breeding even before plant breeding," Muir said. "They have often seen it when they thinned a stand of trees, it had much better yields. The key to making this system work for increased productivity is tracking the pedigree of plants and animals to know which ones are most likely to be passive."
Muir also is director of the Molecular Evolutionary Genetics Graduate Training Program.
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