Beef Cattle

Watch out for heat stress on fescue pastures


Adaption and Use of Tall Fescue in the United States. Shaded areas represent areas of major and minor use.

Adaption and Use of Tall Fescue in the United States. Shaded areas represent areas of major and minor use.

Tall fescue dominates the transition zone between the temperate and subtropical zones of the United States and accounts for over 40 million acres of forage land. Roughly 20% of the total U.S. beef cattle herd is raised in this region. The majority of tall fescue grown is infected with an endophytic fungus. This endophyte is known to produce toxic ergot alkaloids that negatively affect cattle performance. Cattle consuming endophyte-infected fescue experience production losses exceeding $600 million per year. One of the specific negative effects is increased body temperature in cattle grazing infected fescue. 

Fescue-induced heat stress is believed to be caused by several factors. The ergot alkaloids are known to interfere with blood flow from the core to the peripheral tissues. Additionally, the ergot alkaloids have been shown to interfere with copper utilization in the animal, resulting in delayed shedding of winter coats.

Ergot alkaloids constrict blood flow in the peripheral tissues. This directly impedes the animal’s ability to dissipate heat through evaporative cooling. One study showed a 50% reduction in blood flow to the skin over the ribs of steers fed a high-endophyte diet. 

Research has also shown that ergot alkaloids interfere with copper nutrition in the animal. The ergot alkaloids make the plant less able to uptake copper from the soil and make the animal less able to absorb copper during digestion. One of the most noticeable symptoms of copper deficiency (and also fescue toxicosis) is a rough hair coat and significant delays in shedding winter coats. 

Delayed shedding of winter coats contributes to heat stress in cattle on fescue pastures.

Delayed shedding of winter coats contributes to heat stress in cattle on fescue pastures.

This extra hair coupled with decreased peripheral blood flow results in increased body temperatures. During the heat and humidity of the summer (particularly in more southern regions), the animals’ inability to dissipate its body heat results in significant heat stress. Heat stress is very hard on cattle and results in decreased feed intake, reduced weight gain and milk production and poor breeding efficiency.

Many management techniques can be employed to help deal with heat stress, particularly that caused by fescue. These include:

Providing adequate access to cool, clean drinking water: Access to cool water is essential to helping the animal cool its body temperature. Locate waterers in shady locations and keep above-ground water lines shaded. Managers should check water temperature at the trough. An increase in water temperature from 70–95° F will more than double cattle water requirements!

Providing shade: During very hot periods, make sure cattle have shade during the hottest parts of the day. Avoid using pastures that don’t deliver this relief.

Rotating cattle to non-fescue pastures: Research has shown that cattle body temperatures will recover somewhat within 3–12 days when cattle are removed from infected fescue pastures. However, complete recovery from the effects of fescue toxicosis is not likely in the short term.

Keeping fescue seed heads clipped: If pasture rotation is not an option, manage pastures to minimize the amount of seed heads consumed by cattle. The endophyte concentrates in the seed head, making it a very potent source of ergot alkaloids. You can avoid seed heads by grazing pastures close or by regularly mowing if cattle aren’t able to keep up with forage growth.

Providing access to high-quality mineral supplementation: The reasons for this are two-fold. First, we know that cattle have a higher water requirement during periods of heat stress, and thus they will have higher urine output. Cattle will quickly lose essential electrolytes such as sodium and magnesium under these conditions. Additionally, we know that the fescue endophyte interferes with copper nutrition. Given that copper interacts with several other minerals in the body, the fescue endophyte ends up throwing many minerals off balance. Supplementation with a high-quality mineral and vitamin supplement with adequate levels of potassium, magnesium, salt, copper, zinc and other trace minerals and vitamins will go a long way toward balancing out the nutritional shortfalls caused by fescue-induced heat stress.

We can nutritionally fortify our cattle to be better equipped to deal with the adverse effects of heat stress caused by the fescue endophyte. One of the easiest ways to do this is with the ULTRALYX® Fescue + Tasco® Low Moisture Block. This highly palatable supplement is specially formulated for cattle on fescue forages and contains essential electrolytes in addition to a high-quality trace mineral and vitamin package and Tasco. ULTRALYX Fescue + Tasco contains enhanced levels of copper and zinc, in addition to balanced levels of other essential trace minerals. Studies have shown that the addition of Tasco to cattle diets had a positive effect in lowering body temperatures.

In summary, heat stress is a genuine concern for cattle owners utilizing fescue pastures during the summer months. You can help cattle regulate their body temperature by providing cool water and shade. You can also limit the amount of ergot alkaloids ingested by limiting grazing of fescue seed heads. Finally, you can nutritionally fortify cattle to handle heat stress better. One such nutritional option is ULTRALYX Fescue + Tasco Low Moisture Block.

Visit your local ULTRALYX dealer for more information on available ULTRALYX products or call 1-888-718-3493 to speak to an ULTRALYX representative.