Science - January 19, 2011

DNA revolution in animal breeding

Animal breeders have recently been able to speed up the process of establishing the breeding value of a bull by using DNA know-how. This opens up new possibilities, such as breeding dairy cows with a small ecological footprint and a lot of unsaturated fats.

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Sunny Boy the bull is considered by Dutch animal breeders as the ideal bull. He had a gene combination which resulted in female offsprings capable of very high milk production. Sunny Boy (1985-1997) had impregnated countless cows, shown by the 1.8 million straws filled with sperms which had gone over the counter. He had contributed to the increase in the number of dairy cows producing 100,000 litres of milk each in their lifetime.
Five years
However, it took some time before the value of Sunny Boy became clear. In the past, while animal breeders knew how good the father and mother of a newly born calf were, they did not know whether the newborn had inherited its parents' traits. Much variation can also be found among siblings. A young bull has to be one and a half years old before he can produce enough sperms to impregnate a cow. After that, the daughter of the bull has to give birth to a calf and produce milk before the breeder can calculate the breeding value based on the milk production. It therefore took about five years altogether to determine the breeding value of Sunny Boy.
DNA markers
Today, the breeding value of a bull can be determined one day after its birth. This is a revolution with major consequences for the breeding industry, says Sander de Roos. He heads the Breeding & Support department of CRV, a cattle breeding company. He will get his PhD in genomic selection on 21 January under breeding professor Johan van Arendonk. 'We estimate the breeding value of bulls and cows based on DNA markers: pieces of DNA which predict the characteristics of the bull or the cow.' Breeders are now able to use DNA information not only to determine the breeding value much more quickly, but also more accurately.
Milk composition
CRV now works on this aspect together with dairy farmers. When a bull calf is born, the farmers send to CRV a packet containing some of the calf's hairs. 'We then send this to a lab in Luik to be analyzed. The DNA of the bull calf will be analyzed based on 50,000 markers or positions on the DNA. The lab does this DNA analysis, and we have the formula to estimate the breeding value using the DNA markers.' CRV appraises about forty characteristics. These include not just the amount of milk, but also its composition: the amount of fats and proteins. The outward characteristics of the cow - including the quality of its limbs and the udder - are also used to determine the breeding value. A third aspect CRV appraises is the genetic predisposition concerning health, fecundity and life expectation of the cow. CRV can now select these aspects more effectively than in the past. The new technique can double genetic improvement every year, according to De Roos.
Cattle genome
He began his PhD research in 2006. 'Genomic selection was only a theory then.' Since scientists mapped the cattle genome and found many DNA markers, the technique can now be applied by companies such as CRV. De Roos solved a number of statistical problems in his thesis, including the reliability of the breeding value based on DNA markers. He also established how to apply genomic selection in breeding programmes.
Inbreeding
A major issue in each breeding programme is inbreeding. 'I conclude that genomic selection will result in less inbreeding per generation. This is good news to the geneticist. But be aware that as we use young bulls as father animals, we are bringing out more generations in the same period. As such, inbreeding per year can increase. This is what the industry is concerned with.' To limit inbreeding, there must be enough variation in the offsprings.
Ecological footprint
De Roos thinks that genomic selection can be used in the future to improve several new characteristics. For example, he wants to find out if the ecological footprint can be reduced via breeding, by selecting better feed efficiency. Milk composition could also be made more easily adjustable. 'The relation between unsaturated and saturated fats is passed down genetically. Since we know the DNA markers for milk composition, we would be able to predict the milk composition. That will create chances for specific dairy products.'
Sander de Roos will defend his thesis on 21 January under Johan van Arendonk, professor of Animal Breeding and Genetics.

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