Domestic animals: new El Dorado for geneticists
6/3/08

Bulls with bad genes…

Danish RedFollowing this same approach to genomics, the laboratory of animal genetics at the University of Liège has taken an interest in recent years in the genome of certain breeds of cattle that breeders prize. Genetic selection among stock animals is without doubt as old as agriculture. Human beings understood very early on that their immediate interest, in seeking to reproduce stock animals, was served by selecting animals that had the most desirable qualities: docility, strength, endurance, quantity of meat produced, quantity of milk, etc. The equation that our ancestors knew runs like this: a good male plus a good female equals the best chance for a good line of stock. During thousands of years, this empirical approach to genetic selection established in every corner of the globe various specialized and divergent breeds. Breeders living in mountain areas, for example, preferred hardy animals that were smaller in size and better adapted to mountain grazing, while breeders living on plains attempted to breed larger cattle.

Then the revolution of artificial insemination occurred. In order to reproduce, and thus to affect the gene pool, a bull no longer had to be physically present in order for insemination to occur. His sperm plus a syringe was enough… And thanks to techniques for freezing semen, a single male can reproduce not 10, not 100, not 1000 times, but millions of times! There are, for example, tens of millions of cattle of the Holstein breed in the world, but almost all of them are the descendents of “founding fathers”, a handful of famous bulls whose sperm made fortunes for their owners. The problem is that one of these founding fathers, who was called Ivanhoe, had at least two genetic weaknesses that are widely shared among all his posterity. The first causes a fatal immune deficiency at birth that affects 1 out of 500 calves. American breeders estimated that this defect is responsible for $5 million a year in economic losses. The second mutation, which affects 25% of the breed, can cause malformation of the vertebrae.

Holstein“It is therefore urgent,” explains Carole Charlier, senior researcher for the FNRS, “that we monitor the appearance of these congenital diseases in the bovine population, identify as quickly as possible the gene that is responsible, develop diagnostic tests, and get this capability to breeders, so they will stop using animals that carry these genes for reproduction.” Precisely the task that Carole Charlier began working on several years ago in the animal genomics laboratory directed by Michel Georges. Five diseases on the rise were selected because of their economic impact: two forms of congenital muscular dystony (CMD 1 and 2), crooked tail syndrome (CTS), renal lipofuscinosis (RL), and fetal ichthyosis.

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