Growth Rate and Function of Skeletal Muscles in Japanese Quail Selected for Four-Week Body Mass

Abstract

We compared growth and physiological function in pectoral and leg muscles of Japanese quail chicks from a line selected for 4-wk body mass (P line) and an unselected control (C) line. Growth rates of pectoral and, especially, leg muscles were higher in the P line than in the control line during the first week posthatching but not thereafter. Citrate synthase (CS) activity in pectoral muscle increased early in postnatal development but reached much higher levels in control chicks than in selected chicks; metabolic response to cold stress also was greater in C-line chicks than in P-line chicks. Pyruvate kinase (PK) activity and potassium concentration increased rapidly during the early postnatal development period and did not differ between lines except that the increase in PK in leg muscle was delayed in P-line chicks compared with C-line chicks. Exponential growth rates (EGR) of leg and pectoral muscles exhibited inverse relations to increasing PK activity that were indistinguishable between selected and control lines. Pyruate kinase activity was normalized to the peak value for each muscle mass within each line to establish an index to functional maturity (M) extending from 0 to 1. The negative relation between EGR and M did not differ significantly between type of muscle or between line. This result is consistent with the presence of a growth rate-functional maturity trade-off that governs the rate of growth of skeletal muscle during postnatal development. Accordingly, the growth response of leg muscles of selected chicks may be related to delayed maturation, as indicated by PK activity. In addition, although the growth rate of leg muscle in unselected chicks during the first week posthatch is less than expected from M, EGR values for leg muscles of selected quail are close to predicted values. Thus, the growth rate of the leg muscles possibly is down regulated in control lines but released in response to selection for rapid growth to realize more fully the growth potential of the muscle at a given state of maturity.