Modeling chemical and physical body composition of the growing pig

In pig growth models, masses of body lipid (L) and body protein (P) are key state variables that can be related quantitatively to chemical and phys- ical body composition for predicting growth response and carcass characteristics. The main chemical constit- uents in the empty body weight (EBW) are water (Wa), L, P, and ash. Within pig genotypes, Wa is independent of L and closely related to P (e.g., Wa = × P b ). The scaling parameter (b) is remarkably constant across pig types, at about 0.855, and represents changes in distribution of P with increasing EBW and differences in Wa-to-P ratios among body pools. The parameter a ranges between 4.90 and 5.62 and seems to vary with pig genotype. The ash-to-P ratio, about 0.20, has little significance on estimates of EBW. Gut fill, the differ- ence between live body weight (LBW) and EBW, ranges between 0.03 and 0.10 of LBW; it varies with LBW, feeding level, diet characteristics, and time off-feed. The