Growth, body composition and feed intake

Summary1. It is assumed that an animal at a given degree of maturity is seeking to grow its lipid-free body at some potential rate and to attain its inherent fatness. It is also seeking the resources that it needs to achieve these purposes.2. To measure the potential growth rate and inherent fatness of a given genotype, at a given degree of maturity, certain conditions need to be met among which are: feed must be available ad libitum, the feed must be balanced and not constrain intake and the environment must not be too hot. If these conditions are not met either the actual growth rate or the actual fatness, or both, will not be the inherited potential values.3. The amount of feed energy, measured on a suitable scale, needed for units of growth (as protein retention) fattening (as lipid retention) and scaled maintenance do not differ between genotypes.4. The amount of feed energy needed by a genotype to achieve a given lipid-free weight can be reduced by, (i) increasing mature size, (ii) increasing the scaled rate of maturing and (iii) by reducing mature inherent fatness. Only if the current stock is inherently fatter at the lipid-free weight at marketing is the third course a practical possibility. This appears not to be the case in current broiler stocks.