Since the U.S. dairy industry intensified selective breeding efforts in the 1960s, average milk yield in Holsteins has doubled, but the cattle are less fertile. A comparison of DNA from cattle selectively bred for milk production versus cattle isolated from such practices shows a genetic link between increased yields and reduced fertility.
Researchers at the Agriculture Research Service's Animal and Natural Resources Institute in Beltsville, Maryland teamed up with colleagues at the University of Minnesota to compare the genomes of modern Holsteins with those of UM cattle never exposed to the modern selective breeding practices. The lack of exposure meant that DNA from the UM cattle were genetic time capsules of an era before the selection efforts intensified.
By analyzing 50,000 genetic markers, the researchers found that many of the chromosomal regions associated with increased milk yield were also associated with reduced fertility rates. The results also showed that up to 30% of the Holstein genome may be influenced by standard breeding practices.
The researchers say the results will help Holstein breeders and milk producers better understand tradeoffs between high yield and low fertility when selecting for more profitable dairy cattle.
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