Age-related changes and effect of exercise on the molecular composition of immature equine superficial digital flexor tendons.

The study investigates how early exercise impacts the molecular structure and therefore the mechanical properties of tendon tissue in horses. The research concludes that inappropriate or intense exercise at an early age can reduce the production of polysulphated glycosaminoglycans (PSGAGs), affecting the tendon and potentially leading to long-term damage that is difficult to reverse.

Overview of the Study

• The study involved 43 Dutch Warmblood foals that were divided into three different exercise groups: box-rest (no exercise), box-rest with training, and pasture exercise (open field activity).
• The researchers collected 24 superficial digital flexor tendons (SDFTs) from each group when the foals were five months old. The remaining tendons were collected at 11 months after introducing a period of light exercise to all the foals. The aim was to investigate whether any changes caused by exercise at early age could be reversible or not.

Findings after the Five Months Exercise Period

• Significant changes were noted in DNA content (cellularity), hyaluronic acid (HA), and PSGAGs after five months of different exercise activities.
• The study noticed an exercise-related effect on hydroxylysine content and the number of hydroxylysylpyridinoline (HP) crosslinks.
• Cartilage Oligomeric Matrix Protein (COMP) levels, as measured by homologous inhibition ELISA, varied significantly at five months. They were highest in foals that had been in the pasture and lowest in foals that had rested but underwent forced training.

Findings after 11 Months

• At 11 months, the biochemical parameters of the tendons from the foals of the former box-rest and pasture groups became similar. This indicated that the immature tendon has the ability to recover from a retarded development.
• In contrast, the ratio of PSGAGs per unit of DNA from the former training group was significantly lower than those from other groups. This suggested that the training regimen in the study had a lasting negative effect on the tenocytes, resulting in a decrease of the production of PSGAGs.

Implications of the Study

• Inappropriate or excessive exercise can damage developing tendons, with limited chances of recovery after normalising the exercise level. This could be particularly important in managing young equine athletes.
• The reduced production of PSGAGs due to intense early training can lead to long-term damage in tendons, affecting a horse’s physical capabilities.