Despite warm temperatures early in the new year, winter weather has begun to set in, meaning cows will need more energy to maintain body condition, according to a news release from Oklahoma State University Extension.
To determine the effect of cold on beef cows, first estimate the lower critical temperature — 32 degrees for cows with a dry winter hair coat, said Glenn Selk, Oklahoma Extension specialist.
In general, researchers have used 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.
In the following example, the forecast calls for wind chills that will average about 4 degrees. Therefore the calculation for a cow with a winter dry hair coat would be:
- Step 1: Cow’s lower critical temperature is 32 degrees F.
- Step 2: Figure out expected wind-chill from weather reports (4 degrees wind chill in this example)
- Step 3: Calculate the magnitude of the cold as the difference between the lower critical temperature and the wind chill: 32 degrees minus 4 degrees equals 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 the cold weather event).
However, research has indicated that the energy requirement for the maintenance of beef cows with a wet hair coat is much greater, Selk said.
Cows that are exposed to falling precipitation are considered to have reached the lower critical temperature at 59 degrees. In addition, the energy requirement increases 2 percent for each degree below 59 degrees.
To calculate the magnitude of the cold when the cow is wet would be the difference between 59 degrees minus 4 degrees, or 55 degrees. True energy requirements to maintain a wet cow in this weather would be 2 percent times 55 degrees or a 110 percent increase in energy, which would mean that more than twice the normal energy intake is needed, Selk said.
This amount of energy change is virtually impossible to accomplish with feedstuffs available on ranches, he said. Additionally, for cows accustomed to a high roughage diet, the increased energy intake must be made gradually to avoid severe digestive disorders.
Therefore, a more common- sense approach is a smaller increase in energy requirements during wet, cold weather and extending the increase into more pleasant weather to help regain energy lost during the storm.
Cows that were consuming 16 pounds of grass hay per day and 5 pounds of 20-percent range cubes could be increased to 20 pounds of grass hay offered per day plus 6 to 7 pounds of range cubes during the severe weather event, Selk said.
While this is not a doubling of the energy intake, extending this amount for a couple of days after the storm may help overcome some of the energy loss during the storm and done in a manner that does not cause digestive disorders, he said.
The fact that it is not feasible to feed a wet, very cold cow enough to maintain her current body condition underscores the need for cows to be in “good” body condition at the start of winter.