Serum homocysteine concentration in clinically healthy Thoroughbreds

Homocysteine (HCY) is a sulfur-containing amino acid that is metabolically linked to folic acid (FA) and is recognised as a risk marker for coagulation, vascular, and neurodegenerative disorders in humans and small animals. However, the use of serum HCY in equine medicine is limited due to paucity of research concerning its diagnostic utility in this species. This study aimed to evaluate serum HCY concentrations in relation to age, thyroid status (total thyroxine, TT4), and folic acid (FA) in a uniform group of trained, clinically healthy Thoroughbred geldings.Initially, eighty-eight horses were recruited, with 61 deemed clinically healthy following examination. Older animals (≥ 10 years of age) exhibited significantly higher HCY and FA concentrations, while their TT4 levels were lower. A weak positive correlation between HCY and age was observed. This significant age-related increase in HCY was also confirmed in the subset of 19 horses that had all haematological and biochemical parameters within the reference range. Interestingly, in older horses within this healthy subset, a strong negative correlation was found between HCY and the total number of races (TNR), as well as between FA and cumulative fast work distance (CFWD), suggesting that greater historical training loads are linked to a more favourable HCY/FA profile.This study indicates that age significantly influences HCY metabolism in horses, with serum concentrations increasing in older animals. Additionally, it provides new evidence that an individual's athletic history may affect these metabolic pathways. These findings underscore the importance of considering age and athletic activity when interpreting HCY levels and represent a crucial step towards establishing a comprehensive reference range for HCY in horses.