Cows need more nutritional energy in colder weather. The rule of thumb is that a cow's energy requirements increase 1% for each degree the wind chill is below the 32° F lower critical temperature (LCT) for cows with a dry winter hair coat.
Research indicates energy requirements for maintenance of beef cows with a wet hair coat is much greater. Cows exposed to falling precipitation and having wet hair coats are considered to have reached the LCT at 59° F. In addition, the requirements change twice as much for each 1° change in wind-chill factor — with the energy requirement actually increasing 2% for each degree below 59° F.
This amount of energy change is often impossible to accomplish with feedstuffs available on ranches. And, this amount of energy change in diets of cows accustomed to high roughage must be made gradually to avoid severe digestive disorders.
Glenn Selk, Oklahoma State University Extension cattle specialist, says the more common-sense approach is to make a smaller increase in energy requirements during wet, cold weather and extend the increase into improving weather to help regain energy lost during the storm.
He says cows consuming 16 lbs. of grass hay/day and 5 lbs. of 20% range cubes can be increased to 20 lbs. of grass hay/day plus 6-7 lbs. of range cubes during the severe weather event. Extending this amount for a day or two after the storm may help overcome the energy loss during the storm and do it in a manner that doesn't cause digestive disorders.