Minimizing Heat Stress In Feedlots

By : Ki Fanning, Ph.D. and Jana Gramkow, Ph.D

With one of the coldest winters in years past us, it is hard to believe it is the time of year to think about heat stress. Cattle have an ideal temperature range, their thermoneutral zone, where they have their lowest maintenance energy requirement. Research reported this range to be 23 to 77° F for cattle. Factors such as humidity, hair coat length, plane of nutrition and body condition can all have an impact on these temperature ranges. During summer months, high humidity will lower the temperature in which cattle will experience heat stress because it makes it more difficult
for them to lose heat through panting and sweating.

There are many management practices that can reduce heat  stress. The first one, and most critical, is water supply. Animals consume water and urinate to dissipate heat from the body; therefore, it is imperative that your waterers are cleaned weekly and that the recharge rate and water space is adequate to prevent dehydration and maximize water intake. In the summer, the water space should be at least 2 inches per head. The ration should contain salt to encourage water intake. If you are adding onto a lot, or building a new lot, be sure to size the waterers according to the 2-inch rule instead of the waterer manufacture recommendation, which is usually only 1/2 inch.

Shades reduce cattle’s exposure to solar radiation, as well as reduces ground temperature, but has little to no effect on ambient temperature. Research from 1966 reported that shades could reduce heat load of cattle by as much as 30%. A recent study by University of Nebraska researchers found that cattle provided shade had greater intakes (23.4 vs. 22.9 lbs/day) and average daily gains (4.02 vs. 3.90 lbs/day)  compared to cattle with no shade. Additionally, panting scores were less for cattle in shaded pens, and pen surface temperatures were less than surface temperatures of unshaded pens. When installing shades in your feedlot, the shaded area should be 15 to 20 ft2 per animal. The framed structure should be tall enough to drive a loader underneath, keeping in mind that the taller the shade, the better the air flow. An 80% shade cloth seems to work the best, especially if it is running the length of the mound. Shades should be placed north and south so that the shaded ground is not in the same place all day, preventing the cattle from making a mud hole. It is important to remember that the efficacy of shades is highly dependent on location and the severity of heat in the summer.

Mounds 4 to 6 feet high in the lot provide good drainage, windbreaks in the winter, and elevation into better air flow in the summer. Mounds should be run perpendicular to the prevailing wind and ideally run down the middle of the pen starting at the feed bunk and heading towards the back of the pen.

Sprinklers can also be added to the pens. They should put out drops that are large enough to wet the cattle to the hide. If droplets only coat the hair, it will act as an insulator and actually conserve body heat. Cattle cool by evaporative cooling so as the animal dries the water pulls heat from the body. Sprinklers should be started around 85° F and can run 15 minutes on and 5 minutes off or constantly, making sure that you are not putting out so much water that you are creating a mud hole. Creating a mud hole that covers part of the cattle’s hide in mud acts as an insulator and is counter-productive.

Cattle handling elevates cattle’s body temperature and should be avoided on hot days. If cattle must be handled during hot days, handling times should be scheduled for early mornings, prior to 10 a.m. If you are going to work cattle in the evening, you should wait at least 6 hours after sundown so that the cattle have adequate time to cool down.

Essential Oils can be added to the ration to help alleviate the effects of heat stress on the animal. Research has shown that some essential oils contain compounds, such as capsicum, that are natural vasodilators. Vasodilatation of blood vessels improves blood and nutrient flow, as well as potentially helps the animal release body heat.

Fly Control strategies should be implemented during the spring time to help reduce fly populations during the summer. Flies are an additional stressor that can cause cattle to gather, which reduces airflow. We recommend a combination of at least two fly control strategies from the time of the last hard freeze
of spring to the first killing frost in the fall in your local area.

Evening feedings can be done as 100% of the daily allowance at 4:00 to 6:00 p.m., or 30% in the morning and 70% in the evening, or somewhere in between. This will move the heat of fermentation created by the digestion of feed to the night resulting in cattle staying on feed longer when a heat wave occurs. Cattle do not eat much feed in the afternoon, so the feed ends up setting in the bunk, heating, and going out of condition. The cattle eat their biggest meal prior to the sun coming up in the summer, so if the bunks are slicked late at night then they do not have feed in front of them when they want to eat the biggest meal.

This year has been a challenge and there is no reason to believe that summer will be any different, so in order to maintain good performance through the summer months one or two preventative steps should be taken. If you have questions, please contact one of our consultants. For more information related to heat stress or feedlot nutrition, visit Great Plains Livestock Consulting at gplc-inc.com

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