More Milk Means Reduced Fertility for Dairy Cows

The discovery of a gene mutation in dairy cows which raises milk production at the cost of fertility highlights the perils of modern selective breeding. A collaborative investigation conducted by Danish, Belgian and Finnish scientists suggests that many farmers may inadvertently have bred for a trait which increases embryonic death, and casts doubt on a commonly accepted hypothesis linking poor fertility in dairy cows with the diversion of energy away from developing embryos and toward milk production.

This study was prompted in part by the puzzle of Scandinavia, where milk yield has soared thanks to targeted breeding programmes, but attempts to improve fertility in dairy cows have proved almost entirely unsuccessful.  The researchers collected samples from over 10,000 bulls and performed a genome wide association study. After genotyping these animals, researchers found that breeding for milk production had allowed a recessive allele promoting embryo mortality to flourish – a process termed “hitch-hiking”. Many farmers hope that this finding could lead to practical changes, including screening bulls for the recessive allele and removing mutants from the breeding pool altogether.

This finding is made all the more opportune by the fact that EU quotas for milk production are set to expire in 2015, creating a more open market for milk and other dairy products. Since 2009 national quotas have been increasing by 1% each year, theoretically eroding the value of milk and preparing the market for a ‘soft landing’ in 2015. The demand for milk remains very high in Europe, particularly in the Nordic countries of Norway, Sweden, and Finland, with Finland alone producing between 2,200 and 2,400 million liters per year, and increased fertility could help farmers to take advantage of the new market’s opportunities.

To access the original article, please follow this link: http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1004049