Most beef producers understand that when the weather gets colder their cows need more energy to maintain their body condition. The questions are when do cows start experiencing cold stress and then how much more energy do they need?
When we’re considering cold stress, we need to factor in both the actual temperature and the wind speed to determine the effective temperature. In Table 1 you can see wind speed can dramatically lower the effective temperature the cattle experience. Any kind of available protection, whether natural or man-made, can be very valuable in reducing the amount of wind chill.
The second consideration is just exactly when does a cow begin to feel cold stress? The point of cold stress, or lower critical temperature, depends in large part on the amount of insulation provided by the hair coat. As shown in Table 2, that insulation value changes depending on the thickness of the haircoat and whether it is dry or wet.
As a general rule, for every degree that the effective temperature is below the lower critical temperature, the cow’s energy needs increase by 1 percent. For instance if the effective temperature is 17 degrees F., the energy needs of a cow with a dry winter coat are about 15% higher than they would be under more moderate conditions. That energy requirement jumps up to about 40% higher under those conditions if the hair coat is completely wet or matted down with mud.
One of the ways that the cow responds to cold stress is by increasing voluntary feed intake. The animal’s entire metabolism system increases in activity. Also, the passage rate of roughages through the rumen and digestive tract increases. These changes trigger an increase in the cow’s appetite and voluntary intake. Some observed changes in intake based on temperature are shown in the Table 3.
There are some management considerations that we need to keep in mind regarding changes in feed intake in response to cold stress and the cow’s need for more energy.
- Make sure that water is available. If water available is restricted, feed intake will be reduced.
- If the feed availability is limited either by snow cover or access to hay feeders, the cattle may not have the opportunity to eat as much as their appetite would dictate.
- Be careful providing larger amounts of high concentrate feeds. Rapid diet changes could cause significant digestive upsets.
It’s important to remember that cattle can adapt to short term weather changes relatively well without a significant impact on performance. A cow can deal with a few cold, miserable days without suffering long-term effects. However, ignoring the energy costs of long-term cold stress greatly increases the risk of problems down the road during calving and subsequent re-breeding performance. Any steps that we can take to lower the cold stress the cows have to contend with, such as providing wind and weather protection, help reduce her maintenance requirements.