Several rations are provided in a sequence, each for a limited period of time, in order to closely meet the pig's nutrient requirements. Phase feeding nutritional programs provide rations that meet the protein or amino acid requirements necessary to maximize lean growth rates and feed efficiency. Rations are balanced on a lysine basis rather than a crude protein basis because lysine is recognized as the first or most limiting amino acid in swine diets. Nutritional research suggests the lysine targets change by weight, by sex, and by genetic capacity for lean gain. Split-sex feeding is only a refinement of phase feeding.
Gilts typically have better growth performance and remain leaner at heavier weights.
Barrows generally have similar lean growth rates, but higher feed intakes than gilts. The concentration of protein or lysine required by the two sexes on a daily basis would be different, because the barrows eat more than the gilts. The optimum diet for a barrow would be a lower protein or lysine percentage than for gilts of similar ages. Therefore, split-sex feeding should keep groups of pigs to be more uniform resulting in additional carcass premiums. By supplying the correct diet to each room, split-sex, phase feeding is easily accomplished.