Changes in protein and electrolyte concentrations in the pectoral and leg muscles during avian development

Abstract

The development of functional capacity of skeletal muscle proceeds more rapidly in precocial than in altricial birds and more rapidly in leg than in pectoral muscles. To determine whether protein accumulation and electrolyte differentiation proceed in parallel with functional development, we examined changes in protein (lipid-free dry mass, LFDM), K+ concentrations, and Na+ concentrations in pectoral and leg muscles during postnatal development in altricial European Starlings (Sturnus vulgaris) and precocial Japanese Quail (Coturnix c. japonica) and Northern Bobwhites (Colinus virginianus). Proportion of LFDM in pectoral muscle had a similar pattern of increase in the three species during development, whereas the proportion in leg muscle was slightly higher in bobwhites than in the other two species during the first two weeks. Concentrations of K+ increased and Na+ decreased during development. [K+] exceeded [Na+] for the first time at 4 to 8 days for pectoral muscle and 2 to 8 days for leg muscle in starlings, and at about 5 days for pectoral muscle and 1 to 2 days for leg muscle in quail. Electrolyte concentrations approached adult levels at 13 to 16 days in starlings and 8 to 11 days in both quail. These ages preceded fledging in starlings and first flight in quail by 4 to 6 days. In neonates of each species, the proportion of LFDM was 3 to 5% higher in leg muscle than in pectoral muscle; adult levels of LFDM were achieved 3 to 7 days earlier in leg muscle. Differentiation of the two electrolytes (i.e. crossing of [K+] and [Na+] curves) occurred 2 to 4 days earlier in leg muscle than in pectoral muscle, especially for quail. These results indicate that compositional development of muscle parallels functional development of precocity during postnatal growth. Because the production and maintenance of proteins and the differentiation of electrolytes require metabolic energy expenditure, chemical maturity may compete with growth rate for allocation of energy and nutrients.