Winter is here, and with it can come issues with cold stress in cattle. Wintertime conditions that can lead to cold stress include freezing temperatures, snow, ice, wind and a muddy environment. With a dry winter hair coat, a cow’s critical temperature for cold stress will be around 20° to 30° F. However, a cow’s low critical temperature will vary based on her hair coat thickness, moisture conditions, wind conditions and her body condition score. During periods of precipitation, when the hair coat is wet, the critical temperature is around 59° F because wet hair will lose its insulating quality, and the cow will chill quicker.
When cold stress occurs due to frigid temperatures, cows may exhibit muscle shivering, an increased heart rate, deeper breathing and an increased metabolism rate, resulting in an increase in the cow’s requirement for nutrient and energy intake. In periods of cold weather, cows may also tend to stand around in a wind break or huddle in a group to stay warm instead of grazing, which exacerberates their nutrient needs. Appropriate nutritional supplementation is key to managing cold stress during this time.
A good rule of thumb for supplementation during cold weather is that for every one degree drop below the cow’s critical temperature, a cow’s energy requirement (TDN) increases 1 percent. An example of this would be for a non-lactating 1,200 pound pregnant beef cow, normal intake is around 12.2 pounds of TDN per day. If the temperature drops 20 degrees below her critical temperature, she needs 20 percent more energy, equaling nearly 2.5 more pounds of TDN each day. To supply that increased need, you can feed her an extra 5 pounds of hay (containing 50 percent TDN) each day. This means that when the temperature drops below their critical temperature, the cattle need to be fed better. It is also ideal to use your higher-quality hay at these critical times to provide for the increased needs.
Some spring-calving herds will begin having a few calves in late winter when weather conditions can still be extreme. These newborns can be especially at risk for hypothermia in cold weather conditions. Studies have shown that adjusting the time of day you feed the pregnant cow will affect the time of day when she will have her calf. Evening feeding (5 p.m. or later) has proven to increase the percent of cows that give birth during daylight hours compared to nighttime hours, lessening the risk of hypothermia since daylight hours are generally warmer.