Fibre type distribution, capillarization and enzymatic profile of locomotor and nonlocomotor muscles of horses and steers.

The research paper examined the distribution of fibre types, capillary supply, and enzyme activities in the locomotor and nonlocomotor muscles of horses and steers. Findings showed horses adapted to higher activity levels had a higher oxidative capacity, superior vascularization, and a larger proportion of type IIA fibres compared to steers.

Research Methodology

• Researchers collected muscle samples from three horses and three steers at the time of slaughter. All the animals chosen had similar body weight. However, their levels of activity were different, allowing an assessment of how active lifestyles affect muscle properties.
• Heart tissue, locomotor muscles (responsible for movement), and nonlocomotor muscles were included in the analysis. The study took care to include muscles from different depths within the body, allowing a comparison between deeper and more superficial muscles.

Findings

• The research team performed a biochemical analysis to gauge the activity of key metabolic enzymes. This included citrate synthase (CS), 3-OH-acylCoA-dehydrogenase (HAD), hexokinase (HK), and lactate dehydrogenase (LDH). The activity of these enzymes can reveal the metabolic profile of the muscles.
• They discovered the heart tissue in both horses and steers consistently demonstrated high levels of CS, HAD, and HK, but low LDH activity. Deeper muscles and muscle sections also displayed a more oxidative metabolic profile than muscles closer to the surface.
• When all types of muscles were considered, the researchers found that enzymes CS and HAD were more active, and LDH less active, in horse muscles compared to steer muscles. This suggests that horse muscles operate more efficiently and generate less lactic acid waste (originating from LDH activity).
• Horse muscles exhibited a greater amount of type IIA fibres (fast twitch fibres suitable for aerobic activities) and more extensive capillary supply, which helps to deliver oxygen and nutrients more efficiently. However, the size of muscle fibres on average did not significantly differ between the two species.

Implications

• The results reflect the adaptation of horses to higher levels of activity compared to steers. Higher oxidative capacity, better capillary supply, and more type IIA fibres potentially make their muscles more suitable for sustained activity.
• The observation that the ATPase fibre-typing system did not represent the metabolic profile of muscle suggests that future studies may need to combine biochemical, histochemical and other approaches to better understand the relationship between structure, function, and adaptation in muscles.