Hidden assets

by Jenny Tye

he discovery of genes that play a major role in immune function will soon allow farmers to select for "unseen" health performance traits in improved breeding strategies.

University of Guelph doctoral student Surinder S. Saini, along with pathobiology professor Azad Kaushik, is learning more about the construction of the bovine immune system and how to enhance immune competence in dairy cattle.

The researchers have isolated genes that will provide them with markers to reliably distinguish between different dairy breeds and accurately pinpoint animals with the genetic capacity for good health. This and similar technology from Kaushik's laboratory will also open doors to genetic engineering possibilities, as well as to new disease prevention strategies in dairy cattle.

"Animals are currently selected for visible traits and productivity," says Kaushik. "The advent of antibody gene markers will allow farmers to select for the presence or absence of specific unseen gene patterns that are associated with immune competence."

Kaushik and his team are targeting the gene expression of a certain region of the antibody molecule.

An antibody is a protein molecule circulating in blood that protects an animal against invading pathogens. The functional part of the antibody molecule -- called the variable region -- is the part that binds and neutralizes the foreign agent, called the antigen. Rearranging the genes that lead to the expression of -- or "code" for -- this region results in antibody diversity. This is essential for host-disease defence.

For his study, Saini identified up to 15 genes that code for a specific part of this antibody region in four breeds of cattle -- Holstein, Jersey, Hereford and Charolais. He characterized and cloned the genes and developed DNA probes that can be used to quickly target these genetic sites.

Using these probes, Saini mapped the gene patterns of the different cattle breeds, which he's now using as accurate predictors of each breed's genetic ability to resist disease.

The isolation of antibody genes now makes it possible to develop transgenic cattle that produce specific desired antibodies. Transgenic animals would be created by inserting a specific antibody gene that confers resistance to a certain disease into the embryonic DNA of another animal.

In addition, the researchers hope to develop specific genetically engineered antibodies to add to colostrum ("first milk") supplements for newborn calves. This could be used to prevent diseases such as calf scours, which is newborn-calf diarrhea.

"As the productivity of animals increases, their disease susceptibility also increases," says Kaushik. "Farmers are seeing a rise in many economically damaging diseases. Part of the problem is that as farmers are breeding for high productivity, they are inadvertently breeding for low disease resistance. We hope our work will provide ways for farmers to find a balance between herd productivity and health."

This research is sponsored by the Ontario Ministry of Agriculture, Food and Rural Affairs and the Natural Sciences and Engineering Council of Canada.