Histochemical and morphometric study of the cricoarytenoideus lateralis muscle in the horse

Histochemical and morphometric parameters of the cricoarytenoideus lateralis muscle of the horse are presented. Using myosin ATPase staining after acid preincubation, 3 fibre types (I, IIA and IIC) were identified. Using NADH-TR staining, type I fibres showed high oxidative capacity, whereas type II fibres had high or low oxidative capacity. The type I to type II ratio was of 35:65. This ratio remained constant in the age range examined. Statistically significant (p<0.01) differences were found in values for fibre size between groups of horses weighing more than 500 kg and less than 400 kg. Mean area of type II fibres was greater (p<0.001) than that of type I fibres. There were no significant differences in mean area between left and right muscles in the group of animals with less weight. In contrast, significant differences (p<0.05) in mean area between left and right muscles were found for type I fibres in the group of animals exhibiting a higher weight. The histographical distribution of fibre type areas was unimodal. Most adult horses showed muscle fibre type grouping in the left muscle.