By ROBERT J. VAN SAUN
Mastitis remains the most significant economic draining 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 anytime within the life cycle of the cow there are two critical 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 to minimize bacteria from 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 one of prevention. There are many options to managing mastitis many of which will be addressed in future articles. The topic for this article will focus on potential opportunities of 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 greater risk of infectious disease. Although inflammation is a normal component of the immune response to any pathogen, it is believed any stimulation of inflammatory mediators from environmental stressors may promote a negative response leading to an impaired immune response against a disease process.
The immune response is a high nutritional cost physiologic body function that may negatively impact cow performance (more on this in another article). Cells of the immune response are somewhat unique 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. Fatty acids may modulate immune cell function either promoting or suppressing activity. Short chain fatty acids such as ketone bodies associated with the disease ketosis have been shown to suppress immune cell responsiveness.
As it can be seen the immune system is critically dependent upon proper nutrition suggesting the potential for improving immune function at critical times to prevent infectious disease like mastitis. The current nutrient requirement recommendations for dairy cows do not always account for meeting additional immune cell nutritional needs, thus there is some latitude in modifying diets to potentially improve transition cow immune function. Research from Ohio State University in the 1990s showed increasing vitamin E supplementation above National Research Council (NRC) recommendations greatly decreased mastitis cases as well as severity. This work was incorporated into the 2001 NRC recommendations increasing vitamin E intake from 350 to 1500 International Units/day (IU/d) during the dry period to reduce mastitis risk. Further work by this group showed even higher vitamin E supplementation (4,000 IU/day) had a greater preventive effect. From this work it was determined that cows having blood vitamin E concentrations below 3 micrograms/milliliter (µg/ml) were nearly 9-times at greater risk for mastitis. Dry cows consuming traditional stored forage diets will only maintain a blood vitamin E concentration around 1.5 µg/ml 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 as blood concentration increases by 100 µg/ml 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 higher serum iron or lower serum copper concentrations were at greater 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 too much inflammation. As much as I am emphasizing more essential nutrients to support immune function, we need to remember 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.
So where does this leave us? It comes back to my suggestion that 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 postcalving, including mastitis. Many dry cow diets are stripped down of supplementation to prevent overfeeding, but the minerals and vitamins remain essential to supplement.
The best approach here is to work collectively 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 lowered mastitis risk. Remember that just because the supplement is in the diet this 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 5-8 lb/day. Your nutritionist needs to account for this variation in intake within your dry cow pens to ensure a greater 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 and too a greater extent with more 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.
Source : psu.edu