WARDING OFF THE CHILL: Cold stress a factor in livestock production
December 5, 2014
I just flipped my office calendar to the month of December. Going from November to December didn't seem like a big deal this year. I'm guessing it had something to do with the fact that it has felt more like winter than fall for the past four weeks. In keeping with the cold theme, I'll discuss cold stress and the impact it has on livestock in this week's column.
All animals, including cattle, need to maintain body temperature. When air temperatures are within an optimum range known as the thermoneutral zone, they don't need to expend energy to stay warm or dissipate body heat to stay cool. At the upper end of this range is a temperature known as the upper critical temperature. Above this temperature, cattle pant to cool themselves as they don't sweat very effectively. At the lower end of the thermoneutral zone is the lower critical temperature. When air temperatures are below this temperature, cattle and other animals burn energy to maintain their core body temperature.
The challenging thing about upper and lower critical temperatures is that they are influenced by a number of factors. The upper critical temperature is impacted by things such as hair coat color, the amount of night cooling which occurs, and so on. The lower critical temperature is impacted by things such as hide thickness, hair coat thickness, body condition, whether or not cattle are dry or wet or damp, wind speed, and so on. It is nearly impossible to determine specific numbers for upper and lower critical temperature, since the various combinations of any or all of these factors have an effect on how much heat or cold stress the animal might be under.
Hide thickness and hair coat thickness have a significant impact on the animal's ability to endure cold temperatures. Animals that are adapted to colder temperatures through selection and adaptation, can withstand cold weather far better than animals which have not been selected for or adapted to colder temperatures. Animals with a thick hair coat can withstand lower temperatures much better than animals who have not had a chance to develop a winter hair coat. As winter progresses, and animals develop their winter hair coat, the lower critical temperature actually goes down.
Cattle with a good body condition score (>BCS 5) carry more fat and are better able to withstand colder temperatures than cattle in thin condition (BCS 4 or less). This is another good reason to actively manage cow condition through supplementation, weaning date, and pasture management. The best time to do this is in August and September since temperatures then allow you to manipulate body condition score easily and less expensively than later in the year.
A major factor influencing lower critical temperature is whether or not cattle are dry or wet. Wet or damp conditions, including muddy feedlots, in combination with cold temperatures can be deadly as animals lose the ability to insulate themselves. Beef cattle extension specialists routinely recommend maintaining good pen conditions and reducing mud in feedlot situations as a way to insure calories are not expended on maintenance of body temperature but rather on growth. It is also why rain and freezing temperatures are so deadly to newborn livestock as it becomes almost impossible for them to maintain their body temperatures when these conditions occur.
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Effective wind speed also impacts the amount of cold stress cattle experience. Once the air temperature is below the lower critical temperature, the stronger the wind, the more cold stress. It's important to remember that most anemometers (devices which measure wind speed at weather stations) are placed approximately 10 feet above the ground surface. This means that the wind speed you commonly hear reported on weather reports is not necessarily the wind speed you or your cattle are experiencing. Cattle are smart. When the wind is strong, they naturally look for any shelter or relief in the pasture to minimize its effects. This might be a manmade structure, a clump of trees, or a small hill or other depression. They naturally find ways to reduce the effective wind speed.
In summary, it's important to remember that cold stress has an impact on livestock production. It's also important to realize that there are a lot of things we can do to manage those effects. Making sure cattle are in good condition going into the fall, providing adequate shelter from the wind, and avoiding muddy and wet pen conditions are a few of the things you can do to reduce the impact, both on your animals and on your bottom line, of cold stress.
Lardy is the head of NDSU Animal Science Department.