Faster breeding from using markers in bull selection

For her doctoral dissertation, Research Scientist Nina Schulman from MTT Agrifood Research Finland has identified quantitative trait loci (QTL) affecting milk production, fertility and health traits in Finnish Ayrshire cattle, and evaluated the extent to which the use of QTL information, or marker-assisted selection (MAS), might improve dairy cattle breeding.

GENES STILL IN HIDING

Traditional dairy cattle breeding is founded on production information and other phenotype information collected from animals. The greater the volume of genealogical information available, the more accurate the evaluation that can be made of an animal’s breeding value. Evaluation based on offspring, the progeny test, is an efficient, if slow method of acquiring reliable information on the bull genome. Progeny test information for a young bull is only obtained five years after the onset of semination.

The breeder’s dream is to be able to study animal genes and decide from them directly which individuals are worth selecting as parents of the future generation. Variations in the genomic loci present in the DNA of chromosomes, known as markers, can be employed in the monitoring of gene inheritance.

From the available material on 12 parent bulls and their 493 sons, Nina Schulman’s research identified which QTL are connected with particular economically important traits. Twelve different traits were studied: milk yield, protein yield, protein content, fat yield, fat content, somatic cell score (SCS), mastitis treatments, other veterinary treatments, days open, fertility treatments, non-return rate, and calf mortality. Approximately 150 different markers from 29 chromosomes were typed in the whole genome scans performed on Finnish Ayrshire bulls.

MARKERS ACCELERATE BREEDING

A total of fourteen QTL affecting milk production were detected. Research results included interesting QTL affecting protein and fat yield, and mastitis and fertility.

The second part of the dissertation centred on investigation of the use of genetic markers in the breeding scheme. Research simulated how the selection of animals on the basis of genetic markers would have succeeded in comparison to selection based on the traditional evaluation.

In simulating marker-assisted selection Schulman observed that genetic response was faster with MAS than with traditional selection.

The results of the simulation study demonstrate that marker-assisted selection, combined with embryo transfer, offers a viable alternative to conventional selection by increasing genetic response. In this way young bulls can be preselected within families on the basis of marker information, employing evaluation using offspring information only for the best animals.