Effect of age, sex, and barriers in experimental pens on muscle growth.

Length, width, and depth of pectoralis, supracoracoideus, peroneus longus, gastrocnemius, femorotibialis, iliotibialis, and semitendinosus did not increase proportionately with muscle weight as male broilers aged from 5 to 8 wk of age. Only peroneus longus from the drumstick and semitendinosus from the thigh had maximum percentage increases in length, width, and depth at the same age that maximum percentage weight increases occurred. Barriers 10.2, 12.7, and 15.2 cm high were placed in pens when the chicks were 1 wk old and raised 2.5 cm each week until birds were 8 wk old. Muscles were dissected from male and female broilers at 4 and 8 wk of age. Bird activity from crossing the barriers resulted in weight differences in pectoralis and peroneus longus after 3 wk of exposure and in the supracoracoideus, semitendinosus, and femorotibialis muscles after 7 wk of exposure when compared with values for controls. Differences in muscle measurements attributable to barriers in the pen were found in birds in treatment groups after 3 wk of exposure for iliotibialis (length) and femorotibialis (depth). Increases in muscle measurements in birds after 7 wk of exposure occurred in length of pectoralis, supracoracoideus, gastrocnemius pars externa, peroneus longus, and femorotibialis muscles. Alterations in width were found in pectoralis, gastrocnemius pars interna, and femorotibialis muscles and changes in depth in peroneus longus and semitendinosus muscles. These changes were found to be affected by sex, and a number of sex x barrier interactions were found.(ABSTRACT TRUNCATED AT 250 WORDS)