21 January 2014

4 minute read

A cow's critical temperature is around 20-30 degrees F, explains Professor Jeremy Powell, Professor and Veterinarian at Arkansas University, although varies according to coat thickness, body condition score, moisture conditions and wind.

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, writes Professor Powell.

He continues, 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.

During the winter, because of poor pasture conditions and prolonged hay feeding, cows can also suffer with problems related to protein and energy malnutrition. As discussed, many cows deal with increased nutritional requirements due to colder temperatures, heavy gestation and heavy lactation for those that begin calving.

All of these factors may lead to a problem with the cow’s energy demand exceeding her daily intake. Even though a cow may appear to have a good appetite and exhibit rumen fill, she may be in negative energy balance.

This scenario generally occurs in cows exhibiting poor body condition, and heavy, pregnant heifers are particularly susceptible. Cows that have a negative energy balance may act weak and may eventually get down and become unable to get up. This situation would more likely occur in combination with a cold snap.

Preventing this issue with adequate nutrition is the best approach. To prevent potential problems, producers should take an inventory of body condition scores on the cows in their herd during late fall. Sort cows based on body condition, and supplement the animals that need of better nutrition.

When calculating and planning for winter supplementation, it is important to first have a nutritional analysis performed on your hay. Producers can utilize their county Extension agent to assist them with developing a winter supplementation plan. It is much easier to increase body condition in cows before rather than after they have a calf. High nutrition after calving is directed first toward milk production and feeding cows to gain condition after calving and has little effect on increasing body condition. An ideal body condition score for cows prior to calving is a 5 to 6.

If not dealt with, problems observed in the winter can frequently carry over into the spring of the year. Cows that will calve in below normal body condition could exhibit poor colostrum quality leading to decreased calf immunity and calf health problems. Also, thin cows could have fertility issues during the following breeding season, resulting in lower pregnancy rates. Winter is rarely easy, so plan early to minimize potential problems with cold stress through improved nutritional supplementation this winter.

For more information about good management practices for your cattle operation, contact your county Extension agent or visit our web site at www.uaex.edu.