Comparative study of the collagen content and architecture of the Longissimus muscle in concentrate- and forage-fed male goats

Collagen content and architecture of the longissimus thoracis (LT) muscle were compared between the concentrate- and forage-fed male goats. During the experimental period of 9 to 26 wks old, the former gained 15.7kg in body weight by feeding on commercial concentrate food and Italian ryegrass hay, while the latter gained only 2.4 kg by feeding on hay only. Dry matter, crude protein and crude fat were contained at significantly higher percentages in the LT muscle of the concentrate-fed goats than the forage-fed goats, and conversely, collagen content was significantly higher in the muscle of the latter. However, the collagen pyridinoline content did not differ between them. The myofibers in the concentrate-fed goats (54.0μm) were twice the size of those in the forage-fed goats (25.5μm). The higher content of crude fat (2.89%) in the LT muscle of the concentrate-fed goats was not enough for adipose tissues to develop within the perimysium as marbling. Immunohistochemical methods revealed types I and III collagens over both perimysium and endomysium. Thin collagen bundles were loosely distributed in the perimysium of concentrate-fed goats muscles, and conversely, the perimysial architecture in the forage-fed goats muscles appeared as dense stacks of thick collagen fibers. From these results, it was indicated that the development of loose tissues of slender collagen fibers had an intimate relationship with the rapid growth rate of muscle rather than the development of adipose tissue.