Skeletal muscle histochemistry in male and female Andalusian and Arabian horses of different ages.

The research conducted explores how muscle fiber composition and area evolve in Andalusian and Arabian horses of differing ages and sexes, highlighting the progression from type IIB to type I and IIA fibers as the horses grew older.

About the study

• The researchers conducted muscle biopsies on 143 untrained horses, both Andalusian and Arabian breeds, ranging from 10 days to 24 years old.
• The gathered biopsy samples came from the middle gluteal muscle of these horses.
• The horses were grouped according to their breed, sex, and within five age brackets: A (0 to three months), B (yearlings), C (two to three years), D (five to 10 years), and E (11 to 24 years).

Findings on Muscle Fibers

• As a general trend observed through the five age groups, researchers noted a significant rise in the percentage of the type I muscle fibers, also revealing a marked drop in the percentage of type IIB fibers.
• This gradual increase in the proportion of type I fibers saw an about 100% increase over the course of time.
• Simultaneously, the percentage of type IIA muscle fibers also increased notably but only during the first two or three age clusters.
• The reduction in type IIB fibers was proportionally more significant in IIB oxidative fibers than in IIB non-oxidative fibers.
• Overall, the cross-sectional area for all three types of muscle fibers – type I, IIA, and IIB – significantly grew as the horses aged.

Findings on Sex Differences

• The relative cross-sectional area of the type IIA fibers in any of the age groups was found to be significantly larger in stallions than in mares.
• This increase was found to be at the expense of type IIB fibers, suggesting a higher conversion rate of type IIB fibers to type IIA in stallions than in mares.

In summary, this research provides valuable insights into the muscle structure and its development in horses of different breeds, ages, and sexes. This could have significant implications on the training and injury prevention protocols for these animals.