Abstract
Dystrophic chickens lose its righting ability from the supine position when they are fallen on their back. The wings become stiff and lose its flexible movements, causing a flexion contracture at the elbow joint as the disease progresses. The purposes of this study are (1) to know if a dysfunction of righting motion is a direct reflection of muscle weakness and/or a reduction of wing flexibility, (2) to find an index indicating the degree of a flexion contracture at the joint and (3) to see if the righting exercise on dystrophic chickens improves the wing stiffness and pathological changes in the pectoral muscle.
Age matched normal (line 412) and dystrophic (line 413) chickens were divided into four experimental groups. Group 1: Dystrophic chickens with active exercise everyday for 5 weeks, Group 2: Dystrophic chickens without exercise, Group 3: Dystrophic chickens were exercised for 3 weeks and stopped thereafter for 2 weeks, Group 4: Normal chickens without exercise. The righting exercise, namely exhaustion tests were made everyday. The scores were measured every one week. The wing angle at elbow joint (humerus-ulna angle: HUA) was measured with a goniometer every one week by two recorders. Pectoral muscles of normal and dystrophic chickens from every experimental group were removed at 3rd and 5th week and processed for histopathological examination. Sections were stained with modified Van-Gieson method to evaluate the progression of the myopathy.
Dystrophic chickens lost their wing extensibility from the second week after hatching when they grew without exercise (Group 2). The HUA in normal and dystrophic chickens at 5th week were 138.5 ± 4.8 and 127.2 ± 2.7, respectively. The reduction rate of angles was slower in normal chickens than in dystrophic chickens. Dystrophic chickens in Group 1 retained high level (136.4 ± 3.8) in wing extensibility at 5th week, while ones in Group 3 lost the HUA values rapidly after stopping exercise (130.8 ± 6.6). The scores of exhaustion tests tended to be higher in birds which have higher scores in wing extensibility. The histopathological observations of pectoral muscles revealed that the righting exercise for dystrophic chickens prevented pectoral muscles from the rapid progression of muscle fiber necrosis, the formation of vacuolated fibers, and the connective tissue infiltration and thickening. These results indicate that the righting exercise improved effectively the wing dysfunction and histopathological changes in pectoral muscle of dystrophic chickens.
