You might think a cow’s immune system functions at a near-constant level throughout the year, but it doesn't. These strategies will help you manage those fluctuations.
By Troy Wistuba, Prince Agri Products
Dairy cow health issues, such as mastitis, metritis and elevated somatic cell counts, often result from the stress that dairy cattle experience. To best manage the health of your dairy herds, it’s important to understand the physiological factors of stress and the detrimental impact it has on the health, performance and profitability.
There are numerous sources of stress throughout the lactation cycle of the cow. In most cases, these stressful events are associated with the release of cortisol, an adrenal hormone, known to have negative effects on the immune system’s activity. Oftentimes, dairy producers and nutritionists assume that the cow’s immune system is functioning at a near constant level throughout the year. However, in reality the immune system has numerous fluctuations in functionality depending on exposure to stressful events such as calving, weather changes, feed quality, overcrowding and pathogens. Three stressors in particular known to cause immune system dysfunction are calving, excessive heat and mycotoxin ingestion.
Stressor #1 – Calving
Parturition, or calving, although a one-time-a-year event, can generate immunological stress on multiple levels ranging from pen movements and ration changes to the influence of hormones at calving and the nutrient demands of lactation. Strategies that reduce stress around the time of calving should optimize the chance for success. The goal for a successful calving program should be to reduce the number of metabolic, psychological and pathogenic stresses during the transition period. Our focus should be to reduce the amount of stress through adaptive nutrition (close-up diets) and behavioral management (protected calving pens) prior to calving.
Hypothetically, the immune status of dairy cows is constant during the lactation cycle. But because of many sources of stress – such as calving, feed quality and heat stress – there is actually a lot of variance of the dairy cow immune system. (Source: James D. Chapman, Ph.D., PAS, 2013)
Stressor #2 – Heat Stress
It’s well understood that heat-stressed cows have lower feed intakes and, as a result, lower milk production. In addition, heat-stressed cows also suffer from lower immune function, which can lead to increased mastitis, higher somatic cell counts, lower fertility, etc. The effects of heat stress can be minimized through alternative management practices and nutritional strategies. If cows reduce their intake during heat stress, more nutrients need to be packed into a smaller volume of feed.
Consider these heat stress management tips:
1) Work with your nutritionist to adjust dairy cow rations, considering decreased feed intake.
2) Increase the amount of available water.
3) Increase air flow (be certain air moves freely in all sections of the barn).
4) Use misters in targeted areas.
Stressor #3 – Molds and mycotoxins
Molds and mycotoxins are typically found in dairy cattle feed and disrupt normal rumen digestion. This reduces feed intakes and milk production, but, more importantly, stresses the immune system, increasing the likelihood for disease, culling and, in certain cases, death. Stress, physiological state, nutritional standing and disease status will independently and collectively determine the response of a given animal to a specific mycotoxin level or complex of mycotoxins.
To reduce the effects of mycotoxins on dairy cattle health, consider the following:
• Replace the ration and/or remove moldy feeds from the ration.
• Use inorganic binders to bind mycotoxins and prevent them from being absorbed by the animal.
• Increase nutrients such as protein, energy (fats and carbohydrates) and vitamins in the diet.
• Add a nutritional supplement to the ration to help support the cow’s natural immune system.
Cows experience immunosuppression throughout the year, and the solution is complex and multifaceted. The best strategy to avoid metabolic insults to the immune system is to provide a highly nutritional diet to maximize dairy cow health and help support the immune system. In addition to sound nutritional management, best management practices to maximize hygiene and minimize stressors throughout the year are crucial to helping prevent immunosuppression.
Troy Wistuba, Ph.D., PAS, is a dairy technology manager for Prince Agri Products, Inc. He’s a former animal science professor and specializes in working with producers, nutritionists and veterinarians to meet the nutritional needs of dairy cattle. He can be contacted at Troy.Wistuba@princeagri.com.