Gorden notes that researchers at the USDA’s National Animal Disease Center in Ames, Iowa did a study several years ago in which they mastectomized cows and compared the immune function of the mastectomized cows vs. intact cows. In both groups, there was an immune suppression associated with calving and in that trial there was a sudden increase in cortisol the day before calving in both groups. “There is substantial immunosuppression associated with calving and it is probably presumptive to think that cortisol may be the only element causing this immunosuppression,” Gorden explains.
A 2003 Bovine Veterinarian article described research done by Mark Kehrli, DVM, PhD at the National Animal Disease Center-USDA-ARS that showed that cows with severe metritis or retained placentas mobilized virtually all of their circulating immune cells (e.g., neutrophils) to fight uterine infections. This mobilization left very few neutrophils in the blood stream to fight an infection that might start elsewhere in the body, such as the mammary gland. Kehrli said these cows might develop an infection in the mammary gland that goes unchecked for a few hours until the circulating blood neutrophil numbers are restored from the bone marrow. By that time, it is too late for the cow and the infection in the udder may have grown so much that the disease now overwhelms her with a severe peracute case of mastitis.
Calcium is also involved with immune suppression. There are factors associated with intracellular signaling of mononuclear cells that occur two to three weeks prior to calving. “This has a negative impact on immune function by causing slower movement of these cells into infected areas in addition to the effects of calcium in the periparturient period,” Gorden explains. Research has shown that intracellular calcium plays a vital role in peripheral blood mononuclear cell (PBMC) activation. Calcium deficiency will result in less complete closure of the teat sphincter and will result in increased lying time, thus exposing the cow to more pathogens and result in increased mastitis.
Gorden adds that as cows age, there appears to be a decrease in immune function as evidenced by older animals being more severely affected by infectious agents. This reduced function is related to impaired function of neutrophils along with a reduced production of reactive oxygen species in older animals.
Other factors such as poor nutrition, inadequate vaccination, parasite load, poor environment/high pathogen load, high production, stress and others contribute to immune suppression. “Mastitis, like other diseases, is multi-factorial, so often there is more than one negative factor occurring,” Gorden says. “Immune suppression is more severe with other problems such as retained placenta, twinning, lameness and dystocia.”Increased severity of mastitis.
Deficiency:Decreased neutrophil killing capability. Increased susceptibility to bactericidal infection.
Function: Linked to proper immune function. Essential for integrity of skin, physiologic barriers.
Deficiency: Decreased leukocyte function. Increased susceptibility to bacterial infection. High calcium diets can exacerbate zinc deficiency problems.
Source: Lorraine Sordillo, PhD, The Pennsylvania State University, “Mastitis and Immunology,” Bovine Veterinarian, July–August 1998.