The risk that a cow will develop mastitis is a function of pathogen load at the teat end and the cow’s ability to prevent a bacterial infection from becoming established in the mammary gland.
Practicing good cow hygiene (keeping stalls clean, frequent scrapping of allies and following good milking procedures) will reduce teat end exposure, and good nutrition can improve immune function, thereby reducing infection rates and severity of mastitis.
The highest rates of mastitis generally occur during early lactation, and early lactation is the time when most cows experience negative energy balance, says Bill Weiss, Ohio State University dairy nutrition specialist.
During early lactation, dry matter intake (DMI) by dairy cows is low, whereas nutrient demand is high, which leads to cows being in negative energy balance. Body fat is mobilized to provide the energy needed for maintenance functions and to produce milk.
The energy deficient experienced by most cows usually starts a few days before calving and continues for several weeks after parturition. Normal, healthy cows lose 0.25 to 0.5 body condition score (BCS) units in early lactation and reach their BCS nadir by four to seven weeks of lactation.
Some cows start losing body condition several days or even a few weeks before calving, continue losing condition after calving, and lose more than one BCS unit in early lactation.
The concentrations of nonesterified fatty acids (NEFA) and beta-hydroxybutyrate (BHBA) in plasma increase as cows mobilize greater amounts of body fat, and experiments have shown that both high concentrations of NEFA and BHBA have direct negative effects on the functionality of certain immune cells in cattle, according to Weiss.
Other experiments have found that a statistical link exists between energy balance and the prevalence of mastitis; cows with more severe negative energy loss are at a higher risk for mastitis than cows that lose less body condition. However, during the peripartum period, negative energy balance and elevated concentrations of NEFA and BHBA coincides with numerous other events, including hormonal changes, hypocalcemia, and changes in vitamin status; therefore, it is not possible to determine unequivocally that energy balance has a direct effect on immune function.
But, enough data are available to strongly suggest that excessive mobilization of body fat and the associated increase in NEFA and BHBA during the peripartum period contributes to immunosuppression.