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Mastitis remains the most significant economic disease of dairy cows, with recent research indicating combined direct and indirect costs of $444 for a single case of mastitis in the first 30 days of lactation.

Although mastitis may occur any time within the life cycle of the cow, there are two periods of greatest risk occurring at either end of the dry period.

When the cow ceases milk secretion in preparing for the dry period, there is a loss of the milk “flushing” effect that minimizes bacteria entering the teat opening.

The second high-risk period is at the end of the dry period as the cow starts her lactation.

As with any disease process, the preferred approach is prevention. There are many options for managing mastitis, many of which will be addressed in future articles.

The topic for this article is opportunities for preventing fresh cow mastitis through proper dry cow nutrition.

The dairy cow faces many metabolic and immune challenges in the transition from nonlactating to lactating state.

The focus of recent transition cow research has been on how immune cells alter their function in the period just before and after calving that may lead to increased risk of infectious disease.

Although inflammation is a normal component of the immune response to any pathogen, it is believed that any stimulation of inflammatory mediators from environmental stressors may lead to an impaired immune response against a disease.

The immune response brings a high nutritional cost to body function that may reduce cow performance (more on this in another article).

Cells of the immune response are unusual in that they exclusively require glucose to meet their energy needs.

They also require amino acids to support synthesis of cell signal molecules (immune mediators), antibody production, and cell division.

Other nutrients such as trace minerals like copper, zinc and selenium are required for proper immune cell functionality.

Vitamins A and E have historically been associated with proper immune function, and now vitamin D is considered an important immune modulator as well.

Fatty acids may either promote or suppress immune cell function. Short-chain fatty acids such as ketone bodies associated with the disease ketosis have been shown to suppress immune cell responsiveness.

As can be seen, the immune system is critically dependent upon proper nutrition. Improving nutrition, then, offers potential for improving immune function at critical times.

The current nutrient recommendations for dairy cows do not always account for meeting additional immune cell nutritional needs, thus there is some latitude in modifying diets to improve transition cow immune function.

Research Into Nutrients

Research from Ohio State University in the 1990s showed that increasing vitamin E supplementation above National Research Council recommendations greatly decreased mastitis cases as well as severity.

This work was incorporated into the council’s 2001 recommendations increasing vitamin E intake from 350 to 1,500 international units per day during the dry period to reduce mastitis risk.

Further work by this group showed even higher vitamin E supplementation (4,000 units per day) had a greater preventive effect.

From this work it was determined that cows having blood vitamin E concentrations below 3 micrograms per milliliter were nearly nine times at greater risk for mastitis than other cows were.

Dry cows consuming traditional stored forage diets will only maintain a blood vitamin E concentration around 1.5 micrograms per milliliter without additional supplementation. Studies not finding protective effects of vitamin E supplementation often did not achieve the desired blood status.

Research from the University of Guelph showed beneficial effects of vitamin A supplementation on preventing mastitis cases in the first 30 days of lactation.

It was observed that cows having higher blood concentrations of vitamin A (retinol) were less likely to have mastitis in the first 30 days of lactation.

This research did not define a blood concentration threshold but showed that when blood concentration increased by 100 micrograms per milliliter, there was a 60% reduction in mastitis risk.

Research with trace minerals in dry cow diets has been less definitive in showing marked changes in mastitis risk.

A survey of cows involved in two Penn State feeding trials showed cows with elevated serum iron or low serum copper concentrations were at increased risk for mastitis.

Iron is an essential nutrient for gram-negative (coliform mastitis) bacteria. The cow’s udder produced compounds such as lactoferrin to bind and prevent bacteria from accessing iron.

Copper is important for immune cell function and antioxidant activity to suppress inflammation.

As much as I am emphasizing essential nutrients to support immune function, we need to remember that all nutrients are potentially toxic and when in excess may have negative effects on the immune response.

I am hoping the forthcoming dairy nutrient requirements publication will be addressing immune function as a component to defining nutrient requirements, but don’t hold your breath as there may not be sufficient data to support changes.

Properly Supplemented Diet is Key

So where does this leave us? It comes back to one of my earlier articles indicating the dry cow diet is the most important one on the farm.

We need to properly formulate the dry cow diet to prevent potential disease concerns post calving, including mastitis. Many dry cow diets are stripped of supplementation to prevent overfeeding, but the minerals and vitamins remain essential to supplement.

The best approach here is to work with your nutritionist to properly supplement your dry cow diet and use your veterinarian to evaluate the cows’ response to supplementation to ensure they are achieving desired concentrations associated with reduced mastitis risk.

Remember that having supplement in the diet does not ensure all cows will achieve the desired effects. There is potential variation in intake, especially in overcrowded feeding systems or during periods of heat stress.

Documented variation in mature cow close-up pen intakes is 5 to 8 pounds per day. Your nutritionist needs to account for this variation in intake within your dry cow pens to ensure a high percent of cows consume adequate nutrients.

Also remember there is the potential for antagonistic interactions between nutrients and other dietary compounds that may reduce availability.

For example, vitamin A is degraded in the rumen to an elevated extent with high levels of grain or starch in the diet.

Recently “precision feeding” has become a desired practice; however, I would advocate that we need precision feeding to achieve precise nutrient outcomes in the cow, not just the diet.

Robert Van Saun is a Penn State Extension veterinarian.

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