Stress, the release of cortisol and negative energy balance are other suspected culprits for problems during this critical lactation time.
Cows are more susceptible to infectious diseases and metabolic disorders around the time of calving because the immune system is at its weakest during this time. Mastitis, metritis and other infections respond to treatment much less at calving than at any other point in the cow’s lactation.
We don’t know the whole story about why cows have poorly functioning immune systems around the time of calving, but there are several theories, according to Matt Waldron at the University of Missouri. We know that stress and the release of cortisol at calving suppress the immune system.
Negative energy balance caused by the high demands for milk production and lower prepartum dry matter intake seems like an obvious culprit. Mastectomized cows have been shown to have better immune function than cows with intact mammary glands immediately following calving, indicating that the metabolic demands of the mammary gland stress the immune system. But experimentally induced feed restrictions during lactation have not resulted in the same immunosuppression as at parturition, so negative energy balance by itself doesn’t seem to be the cause.
Over-conditioned cows have a greater risk for inflammation and infection after calving, and the cause-and-effect puzzle is slowly being assembled, according to Waldron. Fat cows are more likely to have higher levels of circulating nonesterified fatty acids (NEFA) and ketones and also accumulate more fat in the liver. Elevated NEFA, ketones and liver triglycerides have all been associated with impaired immune function. Fat cows also tend to have higher levels of unstable oxidizing molecules that react with tissue fat, protein and DNA and contribute to inflammation.
Calcium is involved with proper immune system function. Cows with subclinical or clinical milk fever are more susceptible to mastitis.
So, how do we help immune function during this critical time in a cow’s lactation? Minimizing stress by providing a clean, comfortable environment for transition cows is number one. Avoid calving over-conditioned cows. The high price of cull cows lately should help this situation. Prepartum diets designed to minimize subclinical milk fever may also reduce the risk of mastitis and metritis. Providing adequate bioavailable antioxidant nutrients such as vitamin E, A, and zinc and selenium can help reduce inflammation and duration of infections, according to Waldron.