Summary

The first molecular marker project in Canadian Holsteins is starting as a collaborative venture between the Saskatchewan Research Council's Bovine Blood Typing Laboratories and the University of Guelph. About 100 sons from three sire families will be genotyped for approximately 100 informative microsatellite markers. This information will be matched to the genetic evaluations of the sons for production and type traits in an attempt to locate and estimate the effects of genes contributing to genetic variation. If such genes are found the information can be put to immediate use in genetic improvement programs.

Introduction

Genetic improvement of dairy cattle has increasingly been based on sophisticated, statistical data analysis and information gathering systems to produce accurate genetic evaluations fora wide range of economically important traits. These techniques have been highly effective at promoting rapid rates of genetic improvement. They are, however, a "black box" approach which has no knowledge about the individual genes controlling genetic variation. Phenomenal development in molecular genetic technologies over the past decade has provided a series of techniques for exploring genetic variation inside this black box, at the gene level. With over 70,000 genes embedded in a genome of which 90% has no function, locating all the genes causing genetic variation and describing their function is still a very long way off. However, a partial look inside the black box can be achieved by using a class of molecular genetic markers known as microsatellites.

There are tens of thousands of microsatellites in the bovine genome and the location of nearly 1,000 of these is already known thanks to a worldwide effort in bovine gene mapping. Microsatellites generally do not cause genetic variation in their own right, but do act as markers for the region of the genome in which they sit. If the genome is thought of as a huge book of instructions, then microsatellites are the bookmarks that help us find our place. Microsatellites are particularly useful as bookmarks because each microsatellite typically has several different variants which can be used to trace the inheritance of a particular section of the genome from different parents. Microsatellites are also particularly useful as markers because they can be detected using the polymerase chain reaction (PCR). This is a relatively recent technique for copying minute quantities of DNA many millions of times so that standard laboratory techniques can be used when starting with the minutest sample. Several hundred tests are therefore possible starting from a very small blood sample or a single dose of semen. In anticipation of applications for these technologies, the Bovine DNA Bank was set up at the Saskatchewan Research Council's Bovine Blood Testing Laboratory in Saskatoon in 1994. Historical entries were made from samples currently held at the Bovine Blood Testing Laboratory and the intent is to store a DNA sample for every young bull tested in Canada. This resource is held in trust by the SRC for research in Canada to the benefit of the dairy cattle improvement industry. The first project utilizing this DNA bank is just beginning as a collaborative venture between the SRC Bovine Blood Testing Laboratory and the University of Guelph.

Materials and Methods

One hundred sons of each of three important Holstein sires will be genotyped for approximately 100 informative microsatellite markers. Including the unavoidable typing of uninformative markers, some 45,000 to 60,000 genotype assays will be performed. The families have been chosen so that sons will have their first proofs about the time the first microsatellite information becomes available in mid 1997. The microsatellite information will be matched to genetic evaluations for production and type traits, using a search method designed to locate and estimate the effects of genes that make a major contribution to genetic variation. Additional sons will be genotyped for those regions where significant effects are detected and for regions where a strong suggestion of an effect is found. This two-step approach gives essentially the same accuracy at much lower cost than genotyping all sons for all markers.

Implications

If useful effects are detected, the use of young bulls just receiving their first proof will allow the information to be used immediately in genetic improvement programs. An example is that the male progeny of those sons which are themselves candidates for progeny testing, could be pre-selected on marker information and only those carrying the most favourable marker combinations entered for progeny testing. This could simultaneously increase response to selection and reduce costs. If this first marker project is successful it will be recommended that the technique be applied much more widely and could become a regular part of genetic improvement programs in Canada.

Acknowledgements

Funding provided by the Dairy Breed Research Council, Natural Sciences and Engineering Research Council of Canada, Agriculture Canada and Bovacan.