DIPHASIC ALLOMETRIC GROWTH OF SOME SKELETAL BONES AND THE DIGESTIVE-TRACT IN WHITE LEGHORN PULLETS CONSUMING AD-LIBITUM AND RESTRICTED DIETS

Growth data of some bones (shank, tibia, and keel) and the digestive t ract in White Leghorn pullets, which consumed ad libitum and restricte d diets, were analyzed by mono-and diphasic allometric functions. Fat- free plucked empty body mass (FFEBM) or a functional entity was used a s the independent variable in the equations. Pullets had been fed a lo w-lysine diet or a daily restricted amount of an adequate diet, from 0 to 6 or 7 to 18 wk of age. An additional group of pullets consumed ad libitum a control starter and grower diet. Relative growth of the ske letal bones and parts of the digestive tract, vs FFEBM, was described most accurately by a diphasic model. For each constituent, allometric slopes of the first growth phase (beta(1)) vs FFEBM were smaller than 1 (beta(1) varied from 0.39 to 0.43 for shank and tibia, from 0.48 to 0.73 for the keel, from 0.89 to 0.98 for the total digestive tract, an d from 0.80 to 0.84 for the gizzard, separately). These results sugges t that each of the assessed organs matured earlier than the FFEBM. Exc ept for the keel, which grew relatively faster than FFEBM if an early nutrient restriction had been applied, beta(1) of all other assessed s tructures was similar for all treatments. If the allometric slope Of t he second growth phase (beta(2)) was estimated to be not different fro m zero, then the breakpoint between both phases was defined as the mom ent of attainment of maturity for the respective constituent. The atta inment of maturity of the different body structures confirmed the clas sical growth sequence studies of the Hammond School. No differences in mature weights for the assessed organs between the feeding regimens w ere observed. The results indicated that in studies in which a nutriti onal deficiency had been applied, the weights of several body structur es, most often expressed in terms of weight per 100g BW, are strongly related to the decrease in growth rate of the fat-free body. It was co ncluded that most of the reported effects on growth retardation as a r esult of nutrient restrictions are primarily a consequence of the mobi lization of fat per se.