ALlometric growth of histochemical types of muscle fibers in ducks

Radial growth (fiber cross sectional area) was measured at the midlength of sartorius muscles in Pekin and Muscovy breeds of domestic ducks. Pekins exhibited faster early growth (up to 7 weeks after hatching) while Muscovies exhibited greater divergence between sexes (after 7 weeks). In both sexes of both breeds, radial growth of strong-ATPase fibers failed to keep pace with that of weak-ATPase fibers; allometric growth ratio, k = 0.64 in Muscovy males, k = 0.65 in Muscovy females, k = 0.61 in Pekin males and k = 0.61 in Pekin females (P less than 0.005). At 7 weeks, strong-ATPase fibers showed a greater range in their potential for aerobic metabolism, as judged by cytophotometry of their reactions for succinate dehydrogenase (SDH). Thus, in strong-ATPase fibers, cross sectional area was inversely related to SDH reaction in both Pekin and Muscovy breeds (r = -0.76 and r = -0.43, respectively). Further evidence was found for developmental changes in muscle structure caused by changes in relative fiber length, as proposed by MacCallum in 1898.