Dietary energy formulation
There are two primary means to select ingredients when formulating the energy concentration in swine diets: allowing dietary energy to change as the ingredient is added or keeping dietary energy constant.
Formulating to allow dietary energy to change
Using this formulation method, dietary energy fluctuates as the energy source is included in the diet. In this case, a low energy ingredient decreases dietary energy and is often associated with lower growth rate and poorer feed efficiency. Cost of additional finishing space to achieve the same market weight or loss in revenue from lighter carcass weight must also be considered. The use of this formulation method is economically justifiable if the negative impact on pig value by lowering dietary energy is offset by savings in feed cost or improvements in income over feed cost.
Formulating to a constant dietary energy
Using this formulation method, dietary energy is kept constant as the energy source is included in the diet. In this case, a low energy ingredient is usually combined with a fat source or other high energy ingredient to maintain the same base energy concentration in the diet. The use of this formulation method typically maintains similar growth rate and feed efficiency. Thus, feed cost is an accurate estimate of ingredient value.