The model will then estimate either a weight gain on a given level of intake or estimate the energy requirement to reach a target weight gain. Similarly for the lactation model, either energy intake or weight change can be entered, however litter size and piglet average daily gain must be known. If energy intake is inputted, the model estimates weight change. If the estimated weight change is entered, the model estimates the amount of energy need to support the weight change along with the milk production needed to support the specified piglets' growth rate. Committee member Dr. J.E. Pettigrew, Pettigrew Consulting International, suggests that the introduction of modeling into the current NRC edition is a huge advance.
Nutrient requirements can change with different on-farm circumstances.
The 10 th Edition allows these circumstance to be taken into account when developing feeding programs. The growing pig and sow models provide a greater opportunity for nutritionists to estimate the minimum requirements of different animals. However, the models are sometimes limited by the shortage of definitive data about certain amino acids or other nutrients. Where there was not an abundance of data, such as for valine, the NRC committee provided an estimate that is somewhat higher than previously reported. In nursery diets, valine will probably be only the 5 th or 6 th limiting amino acid depending on the protein source used.