Managing mastitis begins with controlling the factors that make infection more probable. Cleanliness in both the barn and the milking parlor, and proper maintenance and use of milking equipment, are all factors that make infection less likely to occur. Overall cow health also plays a major role in decreasing the likelihood, or the severity, of infection. “Mastitis is the result of a bacterial infection in the mammary gland when it is weakened or overwhelmed,” Robert J. Van Saun, Penn State Extension veterinarian, said, addressing participants in the recent Penn State Mastitis and Milk Quality Conference.

Nutrition is an underlying factor in maintaining optimal health. Healthy cows are less susceptible to infections and more able to launch an immune response to quickly eliminate pathogens that cause mastitis.

And healthy cows are less susceptible to periparturient metabolic diseases. These conditions, such as hypocalcemia, ketosis and retained placenta, can then cause an increase in susceptibility to mastitis.

Why nutrition matters
Nutritional status has both direct and indirect effects on immune functioning. Specific nutrients, including vitamins A and E, copper, zinc, calcium and selenium, play an important role.

If the proper availability of these nutrients, or the ability of the cow to use these nutrients, becomes compromised, the immune response is impacted first, with detrimental effects on growth rates and fertility following. Preventing nutritional deficits throughout the life cycle is a first step in increasing overall immunological health.

“Nutrition never comes through a needle,” Van Saun said. “It comes through a balanced diet.”

The immune system, whose role is to reduce or eliminate pathogens, is a nutrient-dependent system. Preventing any infectious agents that find their way into the teat sphincter from ultimately entering into the mammary gland tissue is crucial. Maintaining the proper level of available nutrients to power the immune system response depends upon a healthy diet.

Physical barriers – intact skin, the teat sphincter and the keratin plug – are all first lines of immunological defense that prevent infectious agents from gaining entry into the cow’s body. Changes in their physical properties – dilation, cracks, tears – can all allow pathogens access.

Without a balanced nutrient intake, the physical barriers to infection become compromised. Factors that cause the teat sphincter to remain open increase susceptibility to infection. Protein status influences the integrity of this smooth muscle, while calcium affects the ability of muscles to contract.

The keratin plug requires proper vitamin A, protein and zinc levels, which affect both the quality and the quantity of the plug and its ability to serve as a barrier to infection.

Should physical barriers not prevent an infection, the next line of defense is the body’s internal response to pathogens. Phagocytic (somatic) cells are some of the most important in mastitis infections.

Phagocytes such as neutrophils and macrophages are the primary ones at work against mastitis. Numerous studies have shown the impact of varying levels of specific nutrients on the ability of phagocytes to respond to infection. Additionally, antibody production is influenced by the availability of energy, protein, copper, zinc, selenium and vitamins A, E and D.

Metabolic disease
An unbalanced diet can lead to increased mastitis infections, not only because essential nutrients aren’t available for the immune system’s infection-combating cells but also by predisposing cows to metabolic diseases. Both a deficit and an excess of essential nutrients can cause disease issues.

Cows with hypocalcemia or ketosis are more likely to also develop mastitis. Hypocalcemia results in mastitis rates eight times greater than normal, Van Saun said. Hypocalcemia both slows the closer of the teat sphincter and alters intracellular activities requiring calcium, thus depressing the immune response.

Vitamin E has been shown to improve retained placenta problems. Vitamin E levels have been statistically connected with mastitis, with numerous studies performed over the past 30 years. Vitamin E levels can decrease the incidence of mastitis as well as its duration should it occur.

Other studies have shown that serum vitamin A levels during the last week prior to calving correspond to the likelihood of mastitis infections in the first 30 days of milking.

Nutrition at critical stages
Basing nutrient requirements primarily on milk production results may mean a compromise in immune function and a resulting increase in mastitis, particularly during dry-off and after calving.

Physical changes associated with the dry period and the initiation of lactation predispose cows to mastitis. At calving, the teat end can be slow to close following milking, due to decreased calcium, for example. Maintaining a higher level of nutrition during these phases may be a key to decreasing mastitis rates.

“Why do we see an increase (in mastitis) right after calving and then a major increase right after dry-off?” Van Saun asked. “Is the mother lacking these critical nutrients when calving, increasing her risk of disease?”

Pathogens in the dry cow environment undoubtedly play a role in the increased infection rates, he said. However, a decrease in lymphocyte and neutrophil activity is seen as well for a period of about two months.

Researchers are looking at this to find out why the immune response is compromised during this time frame. It is believed that nutritional compromises during this period exacerbate naturally occurring hormonal and metabolic factors.

Daily nutritional needs for early lactation cows have been shown to be much greater than during pregnancy, with rapid changes occurring over just a few weeks. The metabolic changes associated with transition period coincide with changes in dry matter intake.

Maintaining DMI during this period, or otherwise increasing nutrient availability, will cause less disruption of the metabolic functioning and help the cow to maintain optimal nutrient levels, thus supporting immunological functioning.

Minimizing the DMI decrease in dry cow diets, maintaining at least 12 to 15 percent crude protein in the diet, providing essential minerals and increasing vitamin A and E levels can all help to reduce the incidence of disease and infection.

Beyond nutrition alone
Cow stress can further cause a decline in dry matter intake, which will exacerbate existing physical and nutritional issues. Stress also causes increased fat mobilization and muscle tissue wasting, which in turn make the cow more susceptible to infection.

Because a cow in transition is undergoing rapid metabolic and physiological changes, any impact from additional stress due to environmental factors, such as overcrowding or changes in the social situation, will be multiplied.

In addition, physical factors during the dry period and initiation of lactation create a hospitable environment for pathogens. The immune system becomes suppressed due to a multitude of factors, all of which are impacted by nutritional status.

The quandary of transition cow management has been a thorn in the side of researchers and farmers, with no absolute answers. Maintaining better nutrition during these stages can both decrease physical problems and promote immunological functioning.

“Feed to energy needs, but not to exceed,” Van Saun said. “It’s all maintaining an appropriate balance for bodily function.” PD

Tamara Scully, a freelance writer based in northwestern New Jersey, specializes in agricultural and food systems topics.

Photo by PD staff.