Nutritional and management practices can have a major impact on a dairy cow’s immune system during the transition period. Minimizing stress in close-up and fresh cows is therefore important in supporting their health, milk production and reproductive efficiency, according to Robert Corbett, veterinarian at Dairy Health Consultation in Spring City, Utah.

Corbett noted that dairy cows experience a suppressed immune system at parturition, caused by the release of the stress hormone, cortisol, which makes them more susceptible to mastitis and a host of other health disorders. Elevated blood cortisol, he explained, causes white blood cells, known as neutrophils, to lose their ability to fight infections.

“Any effort that can be made to reduce stress on the dairy cow will result in an improvement in their immune function, which is their first line of defense against the common infectious diseases that occur around the time of calving,” he said. His remarks came at a Preconference Symposium sponsored by Prince Agri Products at the 2013 Penn State Dairy Cattle Nutrition Workshop in Grantville, Pa.

Corbett outlined cow comfort and other management practices to reduce stress and enhance transition cow health, including avoiding overcrowding and providing environmental cleanliness and milking hygiene. He encouraged producers to maximize dry matter intake, ensure adequate energy and protein in transition cow rations, and provide nutritional supplements to help improve energy and support the immune system.

“Immune-suppressed livestock are more susceptible to infections and may experience challenges to other productive functions,” he said.

Role of blood calcium
To minimize the drop in blood calcium levels at parturition, Corbett recommended feeding transition cows a negative dietary cation-anion difference (DCAD) diet with the goal of reducing potassium (K+) and sodium (Na+) levels and increasing chloride (Cl-) and sulfur (S-) levels. Noting that clinical and subclinical hypocalcemia are major underlying causes of problems in transition and early lactating cows, he said that a high percentage of metabolic disease problems, as well as impaired immune function, are directly correlated to low calcium levels.

Corbett said subclinical hypocalcemia – a drop in blood calcium, but not low enough to be classified as milk fever – can affect 25 percent of first-calf heifers and 50 percent or more of second lactation and older cows if they are not on a negative DCAD ration. “Hypocalcemia is like an iceberg – most of the problem may be below the surface and hard to detect,” he said.  “Laboratory analysis of blood samples from fresh cows within 24 hours of calving is the only way to diagnose subclinical hypocalcemia.”

He said that calcium is often described as the second messenger of the immune system, and important in all muscle contraction including the gastrointestinal tract. “Dairy producers must minimize the drop in blood calcium at parturition to maximize dry matter intake and prevent immunosuppression,” he emphasized.