Dairy cows face year-round stress that can make them more susceptible to disease, resulting in reduced production and significant economic costs to a dairy. Recent research continues to demonstrate the important role nutrition can play in promoting herd health by helping to manage stress by supporting a cow’s natural immune system.

Dairy animals experience stressful events routinely throughout their life spans. Shortly after birth, cows and calves are separated and moved either into calf hutches or the lactation string.

Both the cow and the calf are extremely susceptible to disease at this point. The immune system of the cow is responding to the surge in a stress hormone called cortisol that occurs at calving and is necessary to induce the calving process and milk letdown.

This rise in cortisol can take place several days before calving and can last for 3 to 7 days post-calving.

Circulating levels of cortisol in the blood have a negative impact on the dairy cow’s immune system and leave the cow in a weakened state to fight infection, which may last for several weeks as she is transitioning into lactation.

In fact, most of the metabolic diseases of dairy cows (ketosis, milk fever, displaced abomasum and retained placenta) take place during the first two weeks postpartum, while the cow is experiencing this immune-suppressed condition.

Newborn calves receive colostrum, which provides some protection against disease, but in general, they have a very naïve and poorly developed immune system during the first few weeks of life.

This makes calves susceptible to respiratory and intestinal bacterial and viral challenges that can limit their growth and require the dairy producer to make a significant investment in treatment costs.

Early onset disease challenges may ultimately impact milk production and reproductive efficiency as these replacement heifers join the milking herd.

Calving is not the only time dairy animals experience stress. Other sources of stress may include negative energy balance initiated by the onset of lactation or sudden or extreme changes in feed or weather, which may alter feed intake patterns.

Overcrowding, rough handling, poor cow comfort or exposure to molds, mycotoxins and pathogens are other stress factors.

These conditions, either individually or in combinations, result in an immunological stress, which may lead to profit-stealing diseases such as mastitis, metritis, ketosis, displaced abomasum and even death.

Additionally, these environmental or management-imposed stresses may manifest themselves as elevated somatic cell counts, reduced milk production and increased culling rates of low-producing and sick cows.

Costs of an improperly functioning immune system
According to Dr. Chuck Guard, a professor of veterinary medicine at Cornell University, the financial impact of fresh cow health disorders can mount quickly, as shown in Table 1 .

For example, milk fever costs the dairy producer about $234 per occurrence, taking into consideration milk price, cull-cow price, replacement heifer and labor costs.

Retained placentas cost $259 and ketosis $181 per incident, considering the same criteria as those for milk fever.

Diseased cows also produce less milk and may experience delayed conception, which can lead to being culled prematurely, further contributing to economic loss.

Dr. Stephen LeBlanc, a professor of veterinary medicine at the University of Guelph, indicates that as a result of metabolic events in the period two weeks before calving, reproductive health can be affected anywhere from one to nine weeks post-calving, which can have a negative impact on reproductive performance for weeks to months to follow.

Nutritional intervention to support immune function
Nutrition influences every physiological process in the body and thus plays a pivotal role in a properly functioning immune system and resistance to disease.

Vitamins and minerals are essential for hormone production, tissue synthesis, oxygen transport, energy production and many other metabolic activities that contribute to growth, reproduction, milk production and overall health.

Deficiencies in vitamins A or E, for example, or the macrominerals and trace minerals – calcium, zinc, copper or selenium – can impair the function of immune cells and may result in a decrease in resistance to disease in the dairy cow.

The correct amounts of energy and protein also are critical. Energy is necessary to provide glucose as fuel to allow immune cells to operate, while specific amino acids are required in many key pathways involved in the process of recognizing, containing and killing pathogens associated with bacterial and viral challenges.

Disease challenges of all types have a negative effect on productivity and profitability either from lost milk production, increased veterinary costs or culled cows.

Maintaining optimal immune function can produce healthy cows that are more productive, more resistant to disease and more profitable. PD

References omitted due to space but are available upon request. Click here to email an editor.

D.L. O’Connor
Dairy Technology Manager
Prince Agri Products