Calving is a stressful time for cows, and the weeks immediately after calving are the lactation period in which they are most likely to get sick. In fact, nearly 25% of all clinical mastitis occurs in the first two weeks after calving.
The physical stress of calving is significant. Cows experience a spike in the stress-related hormone cortisol from about 36 hours before to 36 hours after calving.
But Mark Kehrli Jr., DVM, Ph.D., director USDA’s National Animal Disease Center, says the disease window is much wider than that. He says numerous factors related to the transition from pregnancy to lactation contribute to a weakened immune status and high disease susceptibility in fresh cows.
“A large body of research has taught us that the cow’s immune system ‘bottoms out’ in the week or two after calving,” Kehrli says. “The mammary system, along with the gastrointestinal, respiratory and reproductive tract all are at risk of disease incidence as a result.”
He explains that many of the hormonal and metabolic changes that prepare the mammary gland for lactation take place during the two to three weeks before calving. “During this critical period, the dairy cow’s metabolism shifts from the demands of pregnancy to those of lactation, with increased demand for nutrients,” Kehrli says. “Negative energy balances that exist during early lactation may also contribute to impaired white blood cell function and, thus, weakened immunity.”
Kehrli says fresh cows often are harboring subclinical infections that may have been present in the dry period, then these infections begin to win the battle when immunity is compromised around calving time. In other cases, cows are exposed to pathogens through the calving process and are less able to ward them off because of low immunity. That’s why fresh cows also are highly susceptible to metritis, pneumonia and salmonellosis.
With this knowledge, researchers have been investigating new ways to help support transition cows through the critical period of immunosuppression around calving. Included in this work is the development of “immunomodulators” that use elements from the cow’s normal immune system to boost immune function.
“Our research has shown no adverse effects from such treatment, and a significant reduction in the incidence and severity of clinical coliform mastitis in the first week of lactation after an experimental challenge,” Kehrli notes. “We’ve learned that immunomodulators work best in immunocompromised hosts, so the transition period is an excellent time for such compounds to be given to cows, as they should work to restore the immune system.”
He notes commercial products using this technology are now becoming available to the U.S. dairy industry. Still, he advises the continued importance of the other fundamentals for supporting transition cows—excellent nutrition management and a clean environment to reduce disease exposure.