Reduce The Cost Of Heat Stress – for Jul. 23, 2010

Given the relatively cool summers we’ve experienced on the Prairies in the last few years, it hard to believe that parts of Western Canada can easily have weeks of very hot weather until the beginning of September.

Unlike most of us, cattle raised on a drylot do not have the luxury to move out from under a relentless sun or move off black dirt that literary could melt the bottom of your boots. Such heat stress conditions cause not only the suffering of animals, but their feedlot performance, which can invariably lead to long-term financial pain. Fortunately, there are number of things that producers can do to alleviate some of this heat stress for cattle raised over the summer, and therefore reduce its adverse effects upon otherwise profitable feedlot performance.

While there are many ways to anticipate heat stress in cattle, many producers should take a close look at the Temperature- Humidity Index (THI); a gradient humidex scale based on 72 F (22.2 C) and 100 per cent humidity is exceeded.

Without any intervention, a THI of about 80 is considered to be life-threatening to most beef cattle because they start to lose their ability to maintain a normal but life-giving body temperature of 101.5 F (38.6 C). Therefore during very hot weather, it’s entirely possible for people to find an unfortunate victim of heat stress in their feedyards that died from either a fatal heartattack or a heatstroke, when its core body temperature exceeded 107 F.

Surveys in Midwest United States report about a five per cent death loss for drylot cattle being fed in days of the extreme summer heat stress compared to an expected 0.2 percent death loss during more comfortable temperatures. Any such cattle deaths associated with this magnitude of heat stress are rarely seen on the Canadian Prairies because our regular summer weather doesn’t usually lend itself to several months of extreme heat.

Heat stressed cattle tend to be lethargic, breath hard or pant rapidly, while standing around all bunched together under any given shade or if no shade is available, they will often lie in each others’ shadows. Heat-stressed drylot cattle also tend to hang around the waterers (double or triple their normal water consumption), and at the same time have little interest in coming up to their feed bunk to eat.

Poor feed intake during such survival behaviour causes a general reduction of important nutrients necessary for good body growth, results in poor average daily gains, and may force many cattle producers to keep their cattle longer than intended. This adds to overall costs of raising these cattle and therefore may reduce profitability, when these particular animals are sold.

Let’s consider how a modest bout of western Canadian heat stress might adversely impact the balance sheet of a virtual cattle operation, caused by one month of heat stress upon their virtual 1,000 backgrounding 600-lb. steers to be marketed at 900 lbs.

This example is based on three assumptions: (1) feed inventory is somewhat limited, so we want to keep these cattle for 120 days; thereby our target gain needs to be an average 2.5 lb. per head daily, (2) the outside temperatures soars above 30 C every day for one month, which causes cattle feed intake to decrease and in turn causes their daily gain to drop 30 per cent or to 1.75 lb. per head daily, and (3) our contract specifies that no cattle will be bought that are lighter than 900 lbs.

As a result of heat stress, these growing cattle were 22.5 lbs. shy of agreed market weight (re: 30 days x 0.75 lb. loss in average daily gain) and needed to be kept nine days longer (re: 22.5 lb./2.5 lb. average daily gain) than originally planned in order to reach a contractual 900 lb. marketing weight. Since these cattle did back off the bunk ration at the same rate (30 per cent) that caused the same rate of growth loss (30 per cent), it is assumed that once they returned to the same feed intake after the heat stress was over that this “unused feed” would be used to feed these cattle during the extra nine days and thus no loss or increase in overall feed costs would be reported.

In contrast, fixed costs such as yardage (re: labour, fuel and other non-feed costs) would have to be spent for these cattle for an extra nine days. Based upon a conservative yardage rate of 50 cents per head per day, this operation must spend an extra $4,500 or nearly $5 per head to background these cattle. We should always keep in mind that under a more severe period of heat stress than illustrated that there could be more substantial reductions in average daily gain, often a more costly loss of feed efficiency, more time and mediations spent on treating higher rates of sickness and as mentioned any costs due to an increase in mortality rates among heat-stressed cattle.

More producers might be forced to keep heat-stressed cattle longer than we realize because many of our Canadian dry lots or feed lots are designed with winter in mind and not two months of possible heat-stress. Most of our yards offer no shade that typically keeps cattle in direct sunlight for much of the summer days and therefore at times may flip them quicker into a heat stress condition (re: direct sunlight adds 3–4 C to their THI). Furthermore, our feedlots are lined with rows of windbreaks that are designed to reduce arctic windchills despite the obstruction of summer breezes that might easily cool down heat stressed cattle. Last, a built-up manure pack in each a pen might pack a significant amount of heat to warm cattle during the winter, but they also can continue to absorb energy from the sun and generate this heat throughout the summer as well.

A modest investment alone would not warrant to redesign the layout of a Prairie feedyard in order to deal with a couple of months of true western Canadian heat stress. However, we could focus our attention upon making the cattle more comfortable when it does occur.

Of all the technique we might use to combat heat stress in summer-fed cattle, we should always make sure that cattle receive as much clean water as they want to drink. For example, an 800 lb. steer requires normally about nine gallons of water per day, but when under heatstress will drink about 15 gallons of water, which initiates the recommendation that about two gallons of water should be provided per 100 lbs. of body-weight for most classes of beef cattle.

Some field studies show that the temperature of the drinking water is equally important and that the temperatures of a water source of over 25 C can actually increase the water requirement of heat stressed cattle. It should also be recognized that the water surface area accessible to cattle should be sufficient for a large number of cattle to drink at the same time, and the water flow within the waterers or tanks be able to replenished water, quickly.

Despite widespread research that dictates cattle significantly reduce feed intake on the days that they would rather spend in front of a waterer, it probably isn’t a good idea to make significant changes to their grower diets in order to compensate for a loss of nutrient intake. Some nutritionists recommend that such beef total mixed rations (TMR) be subtly formulated with higher levels of potassium (1.5 percent), sodium (0.45 per cent) and magnesium (0.35 per cent). These electrolytes are excreted in greater quantities in the cattle’ urine and sweat during heat stress. In addition, add buffers such as sodium bicarbonate to the diet have been considered to be beneficial to combat subclinical acidosis often brought on by heat stress.

One might also consider changing the time that the cattle are fed. Feed their mixed growing beef ration during the early evening and early morning, when the outside temperatures might be cooler. Ensure adequate bunk space is provided so all the growing cattle can eat without crowding. Clean feed bunks of any leftover feed from the previous day.

After the cattle’s primary water and feed demands are met, it probably is a good idea to avoid handling cattle until cooler temperatures prevail. If cattle must be worked, it is best to work cattle in the late hours of night or during the early hours of the morning (before 7 a. m.). If any animals are put into holding pens, they should not be held for more than an hour. It becomes a matter of not adding to the trauma of heat stressed cattle and leaving them alone.

PeterVittiisanindependentlivestocknutritionist andconsultantbasedinWinnipeg.To reachhimcall204-254-7497orbyemailat [email protected]

About the author


Peter Vitti is an independent livestock nutritionist and consultant based in Winnipeg. To reach him call 204-254-7497 or by email at [email protected]



Stories from our other publications