By Blake Jackson
Cattle rely on three key methods to cool down: radiation, convection, and evaporation. “If your cattle can’t use all three methods, they’ll overheat fast,” warns Eric Bailey, state beef nutrition specialist with the University of Missouri Extension.
High summer temperatures can result in weight loss for calves and reduced milk production. Bailey explains, “Heat stress costs real money.” It leads to slower growth, fertility problems, and general health declines. To combat this, producers should ensure cattle have shade, fly control, sufficient water, and appropriate forage.
Why Tall Fescue Increases Heat Risk
Tall fescue grass, common in the Fescue Belt, can worsen heat stress due to toxic endophytes that release ergot alkaloids. These compounds increase internal body heat by restricting blood flow to the skin, hindering the animal’s ability to release heat. Additionally, these toxins interfere with normal shedding by reducing prolactin, leaving cattle with thick coats during hot months.
Cattle can typically manage temperatures up to 88°F (31°C), but Bailey notes that by late May, cows have likely consumed enough ergovaline to intensify heat stress effects during peak summer.
Even small amounts of ergot alkaloids can harm productivity. “Even ingesting small amounts of ergot alkaloids can result in reduced weight gain and smaller calves, less milk, lower fertility and lighter wallets,” says Bailey.
To protect cattle, Bailey recommends:
- Rotating fescue pastures with clover or interseeding with non-toxic fescue.
- Renovating highly toxic pastures completely.
- Feeding supplements equal to 0.5-1.0% of body weight daily to dilute ergovaline intake.
Controlling Flies to Prevent Bunching
Fly pressure worsens heat stress, especially in cattle on tall fescue. “If your cattle are on toxic tall fescue and they are crowding together to dodge flies, the deck is stacked against them,” Bailey says. Bunching raises heat and humidity levels while reducing cooling.
To reduce flies:
- Drag pastures to disrupt manure-based breeding sites.
- Use fly tags, traps, or parasitic wasps.
- Rotate pastures to interrupt fly life cycles.
- Provide Ample Shade and Space
To prevent bunching, Bailey advises:
- 20-30 square feet of shade per cow.
- Portable shade structures with good airflow.
- Water troughs spaced 50-100 feet apart.
“They fail when it’s hot and crowded,” says Bailey. “Evaporation is the last line of defense in a heat wave, but humidity and fescue toxins can cripple it.”
Photo Credit: gettyimages-jacqueline-nix
Categories: Missouri, Livestock, Beef Cattle, Dairy Cattle