Cold stress discussed as winter persists
Despite a big winter storm that blew through Wyoming late in the week, University of Wyoming Extension specialists braved the weather to gather with local producers in the southwest corner of the state for annual educational programming.
Previously known as Wyoming Utah Ag Days, the event was rebranded as Southwest Wyoming Ag Day this year, held on Feb. 20 at the Roundhouse and Railyards in Evanston.
The one-day conference featured discussions on current livestock markets, multispecies grazing and, to address the area’s recent cold snap and snowy winter conditions, Johnson County Extension Educator Micah Most outlined ways to mitigate cold stress in livestock.
Homeostasis and body temperature
To begin, Most explained the concept of homeostasis, which he defines as “stability while adjusting to ever-changing conditions.”
“Our body systems all operate in homeostasis, whether it is our body temperature or the amount of salt in our blood, our body is always regulating these things around a certain set point,” he stated.
Most noted there are numerous external forces in play which pull body systems in and out of homeostasis and several which influence body temperature specifically, as the bulk of cold stress is related to body temperature.
“There are a lot of things in our environment that try to disrupt the internal body temperature of our livestock,” he said. “Air temperature is the most obvious, and wind speed is a pretty obvious one as well. Humidity also plays a role. Then there is clear versus cloudy skies, as the amount of solar radiation actually making contact with the hide is a factor as well.”
Most said there are also a lot of non-environmental factors influencing the ability of an animal to maintain its body temperature. These include nutritional status, body condition score, available forage, coat or fleece status, genetic influence, developmental stage and production status.
“We have some animals we really have to work to protect, like newborns for instance. When they come into the world, they are wet and they do not have the ability to maintain their core body temperature until they have dried off,” he explained.
“Growing yearling and gestating or lactating females all have additional energy requirements relative to a mature female that is not milking, so being cognizant of production status is also important when temperatures take a dip,” he continued. “Certain groups will need to receive higher priority than others.”
Environmental factors
Additionally, Most reminded producers to be aware of specific environmental factors at play on their operations, as different areas across the state – and even from operation to operation in the same region – experience from different environmental conditions.
For southwest Wyoming specifically, he cited data from the Evanston-Uinta County Airport which shows, on average, a low ambient air temperature of 15 degrees Fahrenheit and a high of 32 degrees Fahrenheit for late February and early March.
While humidity discomfort isn’t generally a factor in the southwest part of the state, wind speed is. According to the same set of data, the area sees an average eight miles per hour (mph) this time of year.
“This doesn’t show any specific spikes in the wind, it’s just an average. But it was plenty windy here earlier this month with 60 to 70 mph gusts recorded at the airport,” said Most. “Cold temperatures and wind speed combined create some really dangerous conditions for our livestock.”
Increasing nutrient intake
According to Most, livestock have a regular body temperature of around 102 degrees Fahrenheit and, in winter months when cattle have a thick hair coat and sheep are in full fleece, they have a lower critical temperature of 32 degrees Fahrenheit and 18 degrees Fahrenheit, respectively.
“Below this temperature, animals have to start expending energy from fat reserves to maintain their body temperature,” Most explained.
“Once they hit this lower critical temperature, they start to shiver. They find ways to mobilize energy reserves in their bodies to increase heat production, but eventually they will hit a point where it can’t be sustained and they lose their ability to regulate their internal temperature,” he added.
As livestock pass this lower critical temperature threshold and begin burning energy to stay warm, nutritional energy requirements increase.
“But livestock can only eat so much. Eventually they will max out, and they won’t be able to keep up with their energy demands,” he noted. “This is when we might start thinking about supplementing protein to improve intake and continue to meet energy requirements.”
Most reiterated, “Feed is a big tool we can use to combat cold stress in our livestock species. Energy demand does increase in the cold, and capacity for intake will become limiting. Any animals in a production state like gestating or lactating are going to have elevated demand.”
He further noted supplementation may include things like high-quality alfalfa or extra grass hay, since roughage generates up to 34 percent of an animal’s body heat as it moves through the rumen, or a source of high-quality protein like distillers’ grains or cake, which improves digestibility of the roughage.
Although there isn’t specific literature implying feeding in late afternoon increases body temperature overnight, Most said it’s likely true since rumination peaks about six hours after feeding.
“We can infer feeding in late afternoon will line up peak heat generation with the coldest overnight temperatures,” he said.
Providing shelter
In addition to increasing nutrient intake, Most said providing windbreaks or other structural relief from Wyoming’s unrelenting wind and harsh temps is a good way to mitigate the impacts of cold stress.
This will also help keep animals dry, since a wet coat enhances cold stress exponentially.
Most explained cattle’s hides collapse when they get wet, causing them to lose their insulating power.
At just 59 degrees Fahrenheit, a mature cow has to start burning energy to maintain body temperature if her hide is wet.
“This is typically of large concern when there is liquid precipitation coming out of the sky,” he clarified. “Snow does not tend to collapse the insulating capacity of the coat in the same way.”
In fact, he noted snow on backs is a good sign, as it indicates there is enough insulation to keep body heat from escaping.
“Sheep tend to be a little more resilient, but they are susceptible at a certain period, especially right after shearing,” he added. “If there is any kind of storm event coming through at this time, shelter needs to be prioritized to keep them dry as best as you can, at least for five to seven days until they get reacclimated to being shorn.”
In conclusion, Most explained windbreaks can include everything from stacked bales, tree lines and snow fence, etc. and reminded producers to be aware of where they erect their windbreaks since they tend to catch snow and cause drifting.
Hannah Bugas is the managing editor of the Wyoming Livestock Roundup. Send comments on this article to roundup@wylr.net.
