One of the key effects of cold temperatures on cows is the need for increased energy for maintenance. Oklahoma State University Extension reports note that 32 degrees F. is generally considered the lower critical limit for cows with dry, winter hair coats, meaning that energy needs increase below that temperature.
Researchers use a rule of thumb that cows' energy requirements increase 1 percent for each degree the wind chill drops below freezing.
OSU provides the following sample calculation for a cow with a winter dry hair coat:
- Cow's lower critical temperature is 32 degrees F.
- Expected wind-chill from weather reports is 4 degrees in this example.
- Calculate the magnitude of the cold: 32 degrees - 4 degrees = 28 degrees.
- Energy adjustment is 1 percent for each degree magnitude of cold or 28 percent.
- Feed cows 128 percent of daily energy amount. If a cow was to receive 16 pounds of high quality grass/legume hay; then feed 20.5 pounds of hay during cold weather event.
Research indicates that energy requirements for maintenance of beef cows with a wet hair coat is much greater and begin to take effect at 59 degrees F. These requirements change twice as much for each degree change in wind-chill factor.
To calculate the magnitude of the cold when the cow is wet would be the difference between 59 degrees minus 4 degrees = 55 degrees. True energy requirements to maintain a wet cow in this weather would be 2 percent times 55 degrees or 110 percent increase in energy. Increasing energy intake to that degree is virtually impossible in a ranch environment without creating severe digestive problems.
Rather than try to meet extreme increases in energy needs during bad weather, OSU specialists suggest using smaller increases in energy requirements during a weather event, then extending the increase into more pleasant weather to help regain energy lost during the storm.