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Virginia Cooperative Extension - Knowledge for the CommonWealth

Energy value of feeds is sometimes hard to figure

Dairy Pipeline: September 2001

Charles C. Stallings
Extension Dairy Scientist, Nutrition

Energy value of analyzed feeds can vary. The reason is each lab usually has a different set of equations for energy calculation. These equations often include fiber (ADF or NDF) but can include measurements for protein, lignin, and fat. Energy is calculated not measured directly. Therein lies the confusion. The new 2001 Nutrient Requirements for Dairy Cattle goes a step further and calculates energy taking into consideration the intake and production of the animal being fed. Higher producers eat more and consequently move digesta through the digestive system faster resulting in less energy being available per unit of feed consumed although total energy consumed may be greater because of greater intake. The new NRC calculates energy from nonfiber carbohydrates, crude protein, ether extract (fat), and neutral detergent fiber assuming certain digestibility of each fraction based on dry matter intake. Feeds that are reduced in energy from the 1989 NRC are forages and whole cottonseeds. High protein feeds are increased in energy and grains not changed much. Assuming intake at 3 times maintenance (not uncommon for a lactating dairy cow) corn silage in 1989 had been assigned a net energy value of .73 Mcal/lb. of dry matter. The new NRC reduces this to .71. Whole cottonseeds are reduced from 1.01 to .88. Soybean meal is increased from .88 to .96 and roasted soybeans from .99 to 1.23. Assuming intakes at more than 3 times maintenance, which occurs at higher productions, results in reductions to these numbers. The consensus of the 2001 NRC Committee is energy values for some forages and whole cottonseeds should be lower than we have been using in the past. High protein feeds such as soybean meal and roasted soybeans should be increased. As we attempt to fine tune our feeding programs these changes should be considered.

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