Avoid vitamin and mineral deficiencies, maintain your herd’s immune function when temperatures soar.
By D.L. O’Connor, Prince Agri Products
Dairy producers, veterinarians and dairy nutritionists understand the impact that heat stress can have in decreasing milk production and dry matter intake, the most common symptoms for cows experiencing moderate heat stress.
Nutrition can play an important role in supporting the dairy cow’s natural immune system to reduce the effects of heat stress, which are estimated to cost the dairy industry $897 million annually (St. Pierre et al., 2003). Primary losses are associated with, but not limited to, lowered milk production, increased metabolic disorders, poor reproduction and reduced immune function (Wheelock et al., 2010).
Temperature Humidity Index (THI)
Heat stress in dairy cows has been defined as the point at which rectal temperature exceeds 102.6 F with breaths exceeding 60 per minute. Temperature Humidity Index (THI) is calculated based on the relationship between environmental temperature and relative humidity.
Lactating dairy cows experience heat stress when THI rises above 72, with severe heat stress occurring when THI exceeds 88 (Thatcher et al., 2010). Higher-producing dairy cows show more profound symptoms of heat stress as they generate more heat while eating more feed to support higher production levels.
Table 1: Temperature and Humidity combinations yielding a THI of 72 (Zwald, A., 2007)
Table 1 illustrates various temperatures and humidity values that yield a THI of 72, the point at which signs of heat stress begin to develop.
For example, a temperature of 80 F, with a relatively low humidity value of 35%, will yield a THI of 72 and create conditions that could impact health and performance. Factors such as the level of milk production, air movement, sun exposure and duration of these conditions may impact THI values, such that animals may experience more severe heat stress at lower temperatures and relative humidity values (Thatcher et al., 2010).
Heat stress and immune dysfunction
Acute exposure to high environmental temperatures has been shown to cause significant increases in a stress hormone called cortisol in dairy cattle (Stott et al., 1970). It also is well documented that increases in circulating levels of cortisol in the blood have a negative impact on the cow’s immune system and leave the cow in a weakened state to respond to disease challenges and fight infections.
This immune-suppressed condition may lead to profit-stealing diseases such as mastitis, metritis, ketosis, displaced abomasum and, in extreme cases, even death. Additionally, heat and other sources of stress faced by dairy cattle throughout their life span may manifest themselves as elevated somatic cell counts, reduced milk production and increased culling rates of low-producing and sick cows.
Nutrition plays a pivotal role in a properly functioning immune system and providing 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 macro 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 to allow immune cells to recognize and kill pathogens associated with bacterial and viral challenges.
There also are other opportunities to help maintain immune function. For example, field research has demonstrated benefits of the nutritional supplement OmniGen-AF®* in helping to support immune function in dairy cattle which aids in the maintenance of good health and production.
Maintaining sustained, proper nutrition, combined with cow-comfort management practices, gives dairy producers the best line of defense against the negative health and economic impacts associated with dairy cattle heat stress.
*OmniGen-AF is a product from Prince Agri Products, Inc., that can be supplemented to all classes of dairy cattle as part of their regular diet.
D.L. O’Connor is a dairy technology manager for Prince Agri Products, Inc. She can be contacted at Deb.OConnor@princeagri.com. Learn more about Prince Agri Products here.
St. Pierre, N.R., B. Cobanov and G. Schnitkey. 2003. Economic losses from heat stress by U.S. livestock industries. J. Dairy Sci. 86 (E Suppl.):E52–E77.
Stott, G.H. and J.R. Robinson. 1970. Plasma corticosteroids as indicators of gonadotropin secretion and fertility in stressed bovine. Presented at: 65th Annual Meeting, Amer. Dairy Sci. Assoc., Gainesville, Fla.
Thatcher, W.W., I. Flamenbaum, J. Block and T.R. Bilby. 2010. Interrelationships of heat stress and reproduction in lactating dairy cows. High Plains Dairy Conference, Amarillo, Texas.
Wheelock, J.B., R.P. Rhoads, M.J. VanBaale, S.R. Sanders and L.H. Baumgard. 2010. Effects of heat stress on energetic metabolism in lactating Holstein cows. J. Dairy Sci. 93:644–655.
Zwald, A., 2007. Heifer Management Blueprints. Department of Dairy Science, University of Wisconsin.