Temperatures, Humidity a Worrisome

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2:53 PM - Jun 26, 2013 #1

Temperatures, Humidity a Worrisome Combination for Heat Stress in Cattle
on June 26th, 2013 at 6:49 am




STILLWATER, Okla. – Cattle producers would do well to remember a certain well-proven cliché: “If it’s too hot for you then it’s too hot for your livestock.”


Dr. Dave Sparks, Oklahoma State University Cooperative Extension veterinarian and food animal quality and health specialist, said while proficient livestock operators are aware heat stress can be a problem in livestock as summer temperatures increase, they all may not be aware that other factors can enter the equation besides the thermometer reading.

“These same factors can be dangerous to people who handle livestock as well, but they can do things to compensate for the danger,” he said. “When our bodies cannot dissipate heat adequately to maintain a normal body temperature we retreat to the air conditioner, drink more water or get in the shade. Options available to livestock may be more limited.”

One factor that can significantly affect the incidence of heat stress is humidity. Temperature levels that may not pose a threat at lower humidity levels can become dangerous as humidity increases.

For example, consider a 90-degree Fahrenheit day. At just 15 percent humidity, the potential adverse effects on livestock bear watching; livestock drift into the “danger” level at 35 percent humidity, and are considered to be in an “emergency” situation at 65 percent humidity.

Worse, summertime temperatures in the Southern Plains states will exceed 90 degrees most days. At 100 degrees Fahrenheit, just 10 percent humidity is enough to push livestock into the “danger” zone, with 30 percent humidity being considered an “emergency” situation.

“Cattle producers can’t do much to change the humidity, but they can mitigate other problems that may have an additive effect,” Sparks said.

Lack of shade can make a big difference with heat stress. As ruminants, it is normal for cattle to ingest large quantities of forage and then rest and digest.

“The heat of fermentation produced in the rumen must be eliminated and a shady place to rest can aid this process,” Sparks said. “As an experiment, place a thermometer in a shady place and another nearby but just outside the shade on a hot day; note the dramatic difference. Cattle cannot dissipate heat and their body temperature will rise when ambient temperature exceeds body temperature.”

An adequate supply of clean drinking water is important to helping livestock maintain a safe body temperature.

“When cattle are allowed to stand, defecate and urinate in water sources, the palatability of the water can decline until the animals choose to limit their intake,” Sparks said. “Research has shown when animals are fenced out and vegetation is allowed to grow to the water’s edge, the water stays cooler as well as cleaner.”

Endotoxins associated with tall fescue pastures can cause a rise in body temperature of several degrees. This can make the difference between safe and critical conditions even when other factors are marginal.

“That is a prime reason why cattle on fescue pastures can often be seen seeking refuge in ponds or shade when cattle grazing adjoining non-fescue pastures are still actively consuming forage,” Sparks said.

Perhaps the greatest heat stress danger – for humans and livestock – is activity level.

“Avoid working and processing animals when environmental factors approach the ‘danger’ zone,” Sparks said. “If that isn’t possible, perform the activities early in the morning, before the day’s heat buildup begins and after the previous day’s heat buildup has dissipated.”

Sparks warns against processing cattle in the evening, and good reason: It can take several hours for the animals’ body temperatures to return to normal, even though ambient air temperatures might have declined into a more comfortable range.

“Cattle are lost to heat stress every summer, but a little planning and awareness can go a long way towards minimizing these losses,” he said.

Cattle and calves represent the number one agricultural commodity produced in Oklahoma, accounting for 46 percent of total agricultural cash receipts, according to National Agricultural Statistics Service data.

Source: Donald Stotts, Oklahoma State University
Marcia Bennett
Big Spring,TX
214/606/2452

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