February 2019 Articles

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The Importance of Energy —

The Importance of Energy — Managing the feed and forage resources during extremely cold periods is critical to the cow herd. To combat cold stress, the animal must increase its metabolic rate to supply more body heat. This increases dietary requirements, particularly for energy. Research has indicated that energy requirement for maintenance of beef cows with a wet hair coat is much greater. Cows that are exposed to falling precipitation and have wet hair coats are considered to have reached the lower critical temperature at 59 ̊ F. 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% for each degree below 59 ̊ F. To calculate the magnitude of the cold when the cow is wet would be the difference between 59 ̊ minus 4 ̊ = 55 ̊. True energy requirements to maintain a wet cow in this weather would be 2% X 55 ̊ or 110 % increase in energy (which would mean that over twice the normal energy intake is needed.)
Therefore, if we assume an average grass hay containing 10.8% crude protein (CP) and 54.6% total digestible nutrients (TDN), a 1200 pound lactating cow will consume (daily) approximately 3.24 pounds of CP and 16.38 pounds of TDN. Based on Nutrient Requirements of Beef Cattle, we know that she requires 3.00 pounds of CP and 17.60 pounds of TDN daily. With this particular grass hay, we are borderline adequate in CP and 1.22 pounds deficient in TDN (not figuring in the increase in energy requirements if hair coat is wet and 59 ̊!). In order for her to maintain body condition, we must supplement her with an energy source. Approximately 1 Lb. rolled corn = .88 Lbs. TDN; 1 Lb. soybean meal = .84 Lbs. TDN; 1 Lb. whole cottonseed = .93 Lbs. TDN; 1 Lb. cottonseed meal = .77 Lbs. TDN. — Jason E. Holmes, LSU AgCenter