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

The research article analyzed the histochemical (tissue-specific chemical constituents) and morphometric (quantitative analysis of form) properties of a specific neck muscle (the cricoarytenoideus lateralis) in horses and presented remarkable variations concerning the size and types of muscle fibers alongside their grouping distribution.

Histochemical and Morphometric Analysis of Cricoarytenoideus Lateralis Muscle in Horses

• The study analyzes the histochemical and morphometric parameters of the cricoarytenoideus lateralis muscle of horses. The muscle is crucial for the well-functioning of the horse’s respiratory system and voice production.
• Researchers used various staining techniques like myosin ATPase staining and NADH-TR staining to differentiate between different fibre types (Type I, IIA and IIC) identified in the muscle.
• The different fiber types had distinct properties. Type I fibers showed high oxidative capacity, which means they are efficient at using oxygen, making them crucial for sustaining prolonged, less intense muscle activities. On the other hand, Type II fibers displayed either high or low oxidative capacity.

Ratio and Distribution of Fibre Types

• The ratio of Type I to Type II fibres was 35:65. This ratio remains consistent across the age range examined in the study, showing no correlation between the age of the horse and the fiber type ratio.
• The distribution of these muscle fibres in the cricoarytenoideus lateralis muscle was unimodal, meaning that the distribution had a single peak or concentration. This suggests a predominant set of muscle fibers in the horse’s muscle in question. Furthermore, most adult horses showed muscle fiber type grouping predominantly in the left muscle.

Fibre Size Variation

• The study found differences in fibre size between different groups of horses, categorized based on their weight. Horses weighing more than 500kg had a different fiber size when compared to horses weighing less than 400kg.
• The mean area of Type II fibers was larger than that of Type I fibers, and the differences were statistically significant. Type II fibres are generally larger and more powerful, suitable for quick and forceful muscle actions.
• Weight seemed to influence muscle asymmetry as significant differences in the mean area between left and right muscles were found in heavier horses. However, such variations were not observed in horses with less weight.