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Popsci_2014 01542.txt

#Breeding For High Milk Production Created Less-Fertile Cowsafter generations of careful breeding dairy cows around the world produce more milk than ever. At the same time they've actually become less fertile a phenomenon farmers and researchers have worried about for years.**Now a team of European biologists has uncovered one reason behind the decline at least for several types of Danish cattle. The same genes that make cows produce more milk also kill off cow embryos they found. The European researchers found that up to a third of Nordic Red Cattle are missing one copy of each of the same four genes. Like humans cows are supposed to have two copies of all of their genes one from their moms and one from their dads. Having no copies of those four genes is deadly but at the same time having one copy of each makes a cow produce more milk than normal cows that have two copies. Those missing genes are a gift with a dangerous catch. Of course before this study farmers didn't know how all of this worked. They simply chose high-producing cows to breed thus passing on their shortened genes. That's why the genetic flaw is so common in Nordic cows. Inbreeding makes the situation worse but with artificial insemination it's common on farms. Farmers could improve things by checking whether the bulls they use in breeding are missing copies of these four genes Goutam Sahana a Danish geneticist who worked on the study said in a statement. Those that are shouldn't mate with high-milk-producing cows which may be missing those genes too. By preventing animals that are both missing genes from mating with each other a quantum jump in fertility could be achieved in Nordic Red breeds Sahana said. What about cattle in the U s.?This study looked only at Nordic herds so it can't say whether American cows have the same genetic flaws. But American researchers are also looking into genetics for an explanation of fertility declines in cows at home. Last year Texas A&m announced it received a $3 million grant to study the genetics of dairy cattle fertility. After all it's those cute baby calves that keep the farm going. Check out the entire study in the journal PLOS Genetics.**Some hard numbers for the curious: In 1960 the average American Holstein cow gave about 6300 kilograms (13900 pounds) of milk a year. In 2000 the average cow gave 11800 kilograms. In 1970 the average cow needed 1. 8 rounds of artificial insemination to get pregnant. In 2000 cows needed on average three rounds. Cows now also take longer to become fertile again after giving birth to a calf a

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