June 20, 2000
Keep Feedlot Cattle Cool Even in Drought
CONCORD, Neb. — Better understanding the physiology of feedlot cattle could save thousands of head from dying in the summer heat. And much of that understanding is coming about through a National Research Initiative led by a University of Nebraska beef scientist.
 The NRI effort, coordinated by Terry Mader at NU's Haskell Ag Lab here, is helping scientists and ultimately producers, determine what works and what doesn't in keeping fat cattle cool. Last year in Nebraska, 5,000 head of feedlot cattle perished in a very humid late July heat wave. The loss had an economic impact of more than $20 million, Mader said.
Feedlot cattle are fed a high-energy diet before slaughter to fortify the meat with flavor and nutrition. Feedlot steers and heifers can weigh 1,200–1,300 pounds. Generally finished cattle are in the lot for about four months and are at greatest heat risk from July 1–Aug. 15.
Typically, Mader said, two major heat events have occurred each decade since the 1940s—until the 1990s. In 1992, 1995, 1997 and 1999 individual Nebraska producers lost 50 or more head from heat stress.
Heat stress often is preceded by rain or wet weather, followed by a sudden rise in temperatures. The result is hot, humid, uncomfortable conditions. Although this year's drought makes humidity an unlikely factor in heat stress, producers still should plan for ways to keep cattle cool and comfortable to avoid weight loss and death. Also during drought, high temperatures tend to occur early enough in the spring so nights are still cool. Cattle thus are able to adjust to extreme temperatures before summer begins, at which time days are longer and there is less opportunity for night cooling.
Cattle can't perspire much, so they need plenty of water and airflow to help keep themselves cool, but the NRI research is finding other ways to help reduce heat stress.
"Begin imposing these strategies before the heat episodes arise," Mader said, because reacting when the heat occurs is too late.
In cases of extreme temperatures of above 90 F and humidity above 50 percent, cattle need three inches of linear water space per head. That is, if there are 200 head of cattle, there needs to be 600 linear inches of water space. Any additional waterers need to be installed ahead of time, Mader said, so cattle have time to find the water and establish a social order around using it.
At-risk cattle also need to be away from windbreaks and buildings, as they need a breeze of 3 to 5 mph to remove moisture and heat, Mader said.
The NRI work thus far has confirmed three additional facts: that black-hided cattle get hotter; cooling cattle with sprinklers or shade must be done throughout the hot period, if at all; and feeding management can help keep animals cooler.
Seventy percent of feedlot deaths occur in black-hided cattle, Mader said. Their hides get up to 20 degrees hotter than do light-colored cattle and their actual body temperatures increase up to 2 degrees more. That means a black-hided animal's body temperature can reach 104–104.5, compared to a normal 101.5-102.5.
Fat cattle body temperatures usually get hottest about two hours after outdoor temperatures peak, Mader said. Thus, if the outdoor temperature peaks at 4 p.m., cattle body temperature peaks around 6 p.m., although the lag can run as much as four hours behind.
On cooling body temperature, the NRI research found that cattle stay cooler if they don't get overly heated to begin with. Hot cattle suddenly cooled off can die, Mader noted. Their body heat tries to escape through the surface and extremities but cold water on the hide most likely causes blood vessels to constrict so the heat can't escape.
"The brain is telling the animal one thing, but the body is doing something different," the Institute of Agriculture and Natural Resources scientist said. "The key is once you start cooling the animal, you've got to continue until a cooling period arrives," whether it takes a week or a month.
And finally, a managed feeding program can make a difference, Mader said. The main idea is to feed about 80 percent of full feed around mid-afternoon. Eating at that time means metabolic heat will peak 4 to 6 hours later, when the day has started to cool off. If animals already are hot, they'll likely not eat anyway. When cattle are fed in the morning, their metabolic rate peaks during the hottest part of the day.
By eating less later, cattle continue to gain weight at a lower rate but without losing efficiency, Mader said. However, cattle can become dissatisfied and exhibit behavior problems such as riding.
Management feeding programs aren't for everyone, but do provide a means to reduce body temperatures 1 to 2 degrees on a hot day.
Other heat stress tips include:
–Keep current on marketing finished cattle. Ship cattle immediately upon reaching market weight in July and August. Ship so cattle arrive at processing plants before 6 a.m. to allow them a chance to cool down before temperatures rise.
–Avoid working cattle after mid-morning. Processing cattle can raise body heat 1 degree or more.
–If wetting the pen or mounds, wet 20 square feet of pen space per animal. Avoid wetting pens already muddy or after a rain if the ground is already wet.
–If sprinkling, do so in the morning before cattle heat up. Spray large water drops at 5- to 10-minute intervals once or twice per hour. This may require up to 15 additional gallons of water per day.
–Control insects. Large fly hatches occur along with warmer weather. Cattle irritated from biting flies group together to shelter themselves, which could suffocate those in the center.
For more information about heat stress in cattle, see the World Wide Web at http://www.liru.asft.ttu.edu/collab/heat_stress/heatstress.html.
This research is conducted in conjunction with IANR's Agricultural Research Division. Other entities involved in the NRI effort are the U.S. Department of Agriculture Meat Animal Research Center at Clay Center, University of Missouri at Columbia and Purdue University in Indiana. The project began in November 1998 and concludes November 2001, focusing on multi-disciplinary efforts of nutrition, behavior, biometry, bimeterology and environmental physiology. Next year applications of the research will begin in selected commercial feedlots.
06/19/00-CA
Terry Mader - Ph.D.
Animal Science
Professor
(402) 584-2812
Cheryl Alberts IANR News and Publications (402) 472-3030
Department: Animal Science
|
