Understanding Feed Energy

One feed. Several ways to account for energy.

Gross energy describes complete combustion in a calorimeter. Some of that energy leaves the animal in feces; further losses occur in urine and gases. Feeding also generates heat during digestion and metabolism. Energy systems account for these losses at different steps. [1]

Net energy supports maintenance and production. The heat increment is not an extra amount of retained growth energy to add back to NE. A value at one step cannot be treated as the value at every later step. [1]

Use the system designed for the species

Horses are commonly evaluated using digestible energy, often in megacalories (Mcal). Energy comes from carbohydrates, fats, and proteins. Requirements vary with the horse’s size, activity, growth, and reproduction; a concentration alone does not describe daily supply. [2]

Poultry formulations commonly use metabolizable energy. AMEₙ means nitrogen-corrected apparent metabolizable energy; the correction accounts for nitrogen retained in the body. Energy concentration can influence how much feed birds eat, so the supply of other nutrients must be considered with it. [3]

Cattle plans may use total digestible nutrients (TDN), an energy index expressed as a percentage, or net-energy values. NEm refers to maintenance, NEg to gain, and NEl to lactation. These describe different uses and are not interchangeable calorie labels. [4]

Read the denominator as carefully as the number

As-fed values include moisture; dry-matter values exclude it. Match the basis before comparing feeds. Also distinguish energy per pound or kilogram from energy needed per day. Daily supply depends on the amount actually eaten. [5]

Write down three things beside an energy value: the system, the units, and the moisture basis. If one is missing, ask for it. Avoid converting a crude-protein, fat, and fiber guarantee into a confident energy ranking with a generic calorie formula.

What evidence supports the energy value?

Ask whether the figure comes from a feeding study, an ingredient table, or a prediction equation, and whether it applies to your species and the feed you are considering. Bring that information and actual feeding amounts to our nutritionist.

Continue with Carbohydrates & Fiber, Fat in Animal Nutrition, or Beyond Guaranteed Analysis.