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* Department of Animal and Poultry Science, University of Guelph, Guelph, ON, Canada N1G 2W1 and
and
Institute of Food, Nutrition and Human Health, Massey University, Palmerston North, New Zealand
1 Correspondence: phone: 519-824-4120 ext. 56477; fax: 519-836-9873; E-mail: cdelange{at}uoguelph.ca.
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 physical body composition for predicting growth response and carcass characteristics. The main chemical constituents 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 = a x Pb). 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 difference 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 distribution of P and L over the main physical body components (dissectible muscle and fat, viscera, blood, bone, integument) varies considerably among groups of pigs and appears influenced by EBW, pig genotype, feeding level, diet characteristics, and possibly thermal environment and health status. Except for extreme pig genotypes, the distribution of lean over the main carcass cuts is relatively constant; however, little is known about the observed variation in the distribution of L over body fat depots. Representing dynamic effects of animal and external factors on sizes of physical body components is an apparent weakness in pig growth models, further complicated by inconsistencies in defining some of the physical body components, and dissectible lean tissue in particular. Improved accuracy in representing physical body composition will provide more insight on manipulation of carcass value and efficiencies of converting diet nutrients into pork products.
Key Words: Body Composition • Chemical Composition • Growth Models • Physical Properties • Pigs
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