Energy in Practical Formulation – New Research, Industry Trends and Direction and Research Gaps

The cost of feed contributes largely to the cost of pig production and energy represents the largest part of this cost. An appropriate assessment of the energy value of feed ingredients and diets is therefore very important in feed formulation. Likewise, it is important to understand and to quantify how an animal uses its dietary energy, which is often referred to as the energy requirement. To be meaningful, energy values and energy requirements must “talk the same language”. For example, in a net energy (NE) system, the marginal efficiencies with which nutrients are used are attributed to the NE value of the ingredients or the diet. Consequently, these efficiencies are no longer accounted for in the NE requirement. In an ME system, only the material energy losses are accounted for in the ME value of an ingredient and the efficiency with which the energy is used is accounted for in the energy requirement as the cost of energy retention. The choice of an energy system has an important impact on the relative energy values of different feed ingredients and thus on feed formulation. Compared to starch, feed ingredients rich in fat have a higher NE value (compared to an ME value), while protein and fiber-rich ingredients have a lower NE value. Animal performance is better related to the NE intake than to the ME or DE intake and the NE system is therefore the preferred system for feed formulation in many countries. Although a NE system accounts for differences in energy efficiency among nutrients, a large part of the variation in NE values among feed ingredients originates from variation in energy digestibility. Also, the energy digestibility of a given ingredient typically increases with increasing body weight of the animal. This means that the DE value of a feed ingredient is not a property of the diet, but results from the interaction between the animal and its diet. Interactions between the diet and the animal also occur at the metabolic level. The fact that nutrients can be used for difference purposes (e.g., energy retained as protein or lipid, ATP production) has led to proposals to further refine the NE system. It is our belief that a further refinement of an NE systems is useful only if it is also accounts for interactions between the animal and its nutrients, thereby abandoning the very concept of additivity on which feed formulation is based.