Glenn Selk, Oklahoma State University extension animal reproduction specialist, reminds producers of the impact of cold weather on cow energy needs.
“To determine magnitude of cold, lower critical temperature for beef cows must first be estimated. For cows with a dry winter hair coat, the lower critical temperature is considered to be 32 degrees Fahrenheit. Researchers use the rule of thumb that cows’ energy requirements increase 1 percent for each degree the wind chill is below the 32 degree lower critical temperature,” he says.
Step 1: Cow’s lower critical temperature is 32 F.
Step 2: Expected wind chill from weather reports (use 4 degrees wind chill in this example)
Step 3: Calculate the magnitude of the cold: 32 degrees – 4 degrees = 28 degrees
Step 4: Energy adjustment is 1 percent for each degree magnitude of cold, or 28 percent.
Step 5: Feed cows 128 percent of daily energy amount. (If 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. The lower critical temperature for a wet hair coat is 59 F. In addition, the requirements change twice as much for each degree change in wind-chill factor, so the energy requirement actually increases 2 percent for each degree below 59 F.
“This amount of energy change in the diet of cows accustomed to a high roughage diet must be made very gradually to avoid severe digestive disorders,” Dr. Selk says. “Therefore, the more common-sense approach is a smaller increase in energy requirements during wet, cold weather and extending the increase into more pleasant weather.”