By Greg Highfill
Enid News and Eagle
— The recent snow storm has been stressful on livestock and ranchers alike. Resources were stretched just to provide feed and water during this critical time.
Fortunately, producers did have a few days warning they utilized to feed and organize hay supplies, plus arrange needed equipment. Chopping ice to supply water has been an arduous but vital task. In addition to hydration, water is needed to maintain proper feed intake.
The metabolic response of cattle to cold temperatures includes striated muscle shiver, heart beating faster, breathing becomes deeper, urine flow increases and pituitary controlled systems are activated, elevating the biological function of all tissues. The result is an increase in the cow’s requirement for energy.
As snow covers standing forage, providing good quality hay is the most practical way for producers to increase the energy intake of their cow herd. An additional benefit to cattle consuming more hay is the increased heat production from the rumen microorganisms as they digest the forage. In general, hay digestion produces more heat during digestion than concentrate feeds. However, concentrate feeds may become needed for energy intake as requirements spike during wet weather events.
How much to feed
When determining the amount of additional feed needed due to cold weather, the first step is to identify the cow’s lower critical temperature (LCT), which is based on hair-coat, ambient temperature and precipitation. For cows in dry conditions with a normal winter hair coat, the LTC is considered to be 32 degrees. In general, researchers have used the rule of thumb that a cow’s energy requirements increase 1 percent for each degree the effective temperature (wind chill) is below the LTC.
The calculation example for a cow with a dry winter hair coat would be: Determine the cow’s LTC (example: 32 degrees; estimate wind-chilled temperature (example: 20 degrees temperature with 12 mph wind equals 7 degrees wind-chilled temperature); subtract wind-chilled temperature from LCT to calculate amount of difference (32 degrees minus 7 degrees equals 25 degrees below LTC: energy adjustment is 1 percent for each degree magnitude of cold below LTC, or 25 percent; feed cows an additional 25 percent above the normal daily energy amount. If normal is feeding 12 pounds per day of good hay, increase it to 15 pounds.
Wet hair is the enemy
A good winter hair coat can insulate a cow from a lot of cold weather, unless it is wet. Water is an excellent conductor of heat and unfortunately cold as well. Rain results in a greater loss of insulation ability than snow. Energy requirements for maintenance of beef cows with a wet hair coat are significantly greater. Cows exposed to falling precipitation and that have wet hair coats are considered to have reached the LTC at 59 degrees. In addition, the requirements change twice as much for each degree change in wind-chill factor. In other words, the energy requirement actually increases 2 percent for each degree below 59 degrees. To calculate the magnitude of the cold when the cow has a wet hair coat in our earlier example would be the difference between 59 degrees minus 7 degrees or 52 degrees. True energy requirements to maintain a wet cow in this weather would be 2 percent times 52 degrees, or 104 percent increase in energy or double the previous energy intake. This amount of energy change is virtually impossible to accomplish with increased hay intake alone. Feeding high-energy feed grains would be the only practical way to add that much energy to the diet.
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. This is not a doubling of the energy intake, but by extending this amount for a day or two after the storm may help overcome the energy loss during the storm and done in a manner that does not cause digestive disorders.
Positive results
Kansas State University conducted a trial adjusting energy feeding levels during cold weather. The researchers used 60 commercial cows fed in dry lot and fed one-half of the cows a steady diet based upon the thermal neutral requirements for body weight maintenance; the other 30 cows were fed a ration adjusted for 1 percent more feed for each degree of coldness plus the adjustment needed for wet hair coat when appropriate.
Cows on the diet adjusted for weather conditions gained 89 pounds more during last half of gestation, had 17 percent more cows cycling 60 days post calving and were 103 pounds heavier the next fall after the calves were weaned. The amount of additional feed to account for the cold weather events in this trial would be equivalent to 125 pounds of corn per cow. Effective cold weather feeding adjustments can result in better cow body condition and more efficient cow maintenance.
In summary, the cold rain in the weather forecast could be as stressful as the past snowstorm. Producers should: Adjust winter supplement feeding amounts based on wind-chill temperature and hair coat condition; provide wind breaks or shelters, man-made or natural, to reduce exposure to wind, moisture or mud; remember brief exposure to cold stress is less severe than 24-hour continuous cold; and provide water daily.
Highfill is Oklahoma Cooperative Extension Service area livestock specialist.
