For years, dairy producers have bred cows that make more milk, perhaps at the expense of reproductive health. In a recent Journal of Animal Science paper, scientists from the University College Dublin urged researchers to take a closer look at the effects of stress and infections on dairy cow fertility. The review of cow genetics, nutrition, and hygiene could help dairy producers keep their herds healthy and help cows produce more calves.
In an interview, paper coauthor Dr. Mark Crowe explained that cows producing more milk do not necessarily have to have lower fertility. Reproductive health and overall herd health often depends on good animal management.
Monitoring uterine infections is one way producers can improve dairy cow fertility. After a cow gives birth, her uterus can become contaminated with bacteria, like E. coli, that cause long-term inflammation. This inflammation can decrease the cow’s ability to get pregnant a second time. The researchers cited several studies showing that uterine infections suppress the production of the hormones necessary for ovulation.
In their paper, the researchers pointed out that uterine infections often occur at the same time that a cow’s milk yield peaks. They cited a study where 73 percent of high-yielding cows contracted uterine disease, compared with 45 percent of low-yielding cows. This indicates that cows may be using more of their energy for milk production while sacrificing immune system strength. Ceasarian sections, hoof lameness, udder infections and low body weight can also hurt future fertility.
But there are ways to keep high-yielding cows healthy. Crowe said better nutritional management and hygiene during calving can help cows fight infections. He said that better cow breeding could also help producers.
“They need to make a concerted effort to select cows that are genetically good for fertility traits as well as for yield,” said Crowe in an interview.
In the future, Crowe hopes studies of immunity in the uterus and post-partum nutrition could help dairy producers keep their herds healthy.
The paper by Crowe and Williams was based on a presentation to honor the late Dr. H. Allen Tucker at Joint Annual Meeting in New Orleans in July, 2011. The study is titled “Stress effects on postpartum reproduction in dairy cows.” It was published online in November and can be read in full at jas.fass.org.
Dr. Mark Crowe, University College Dublin
Madeline McCurry-Schmidt, American Society of Animal Science
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