Cross sectional area of forelimb metacarpal region flexor tendons in horses of different breeds and age

Abstract

There are few studies on the effects of age within breeds on cross sectional area (CSA) of flexor tendons in horses. This study was designed to evaluate the relationship between age and the CSA of the superficial flexor tendon (SDFT), the deep digital flexor tendon (DDFT) and its accessory ligament (AL-DDFT) of both forelimbs in horses utilising ultrasound. Ages of the horses ranged from 2 years to aged, and the breeds evaluated were Thoroughbred (TB), Standardbred (SB), Quarterhorse (QH) and German Warmblood Riding horse (WB). CSAs were measured with ultrasound at 4 cm intervals, starting 4 cm from the distal border of the accessory carpal bone down to the metacarpophalangeal joint. The CSA of the SDFT in 3-year-old and older TB, QH and WBs was smaller than in the 2-year-olds (all P<0.001) and did not differ between 3-year-olds and older horses (P≯0.05). In comparison, the CSA of the SDFT in 2-year-old and 3-year-old SBs was smaller than in the horses older than 3 years (P<0.05 among age groups). The 2-year-olds had larger CSA of the DDFTs than the 3-year-olds (P<0.01), and the CSA was also larger in the older horses of all breeds (P<0.01). However, the 3-year-old QH and SBs had smaller CSAs of the DDFT than the horses older than 3 years of age, (P<0.001), but interestingly the CSA was not different in the TB and WBs based on age (P≯0.05). The CSA of the AL-DDFT in the left forelimb was smaller than in the right forelimb (P<0.01) of all horses. The results of this study show that differential effects exist between age and within breeds on the CSA of the SDFT, DDFT and AL-DDFT, indicating that training and management may play a role, in addition to genetics, in the CSA of the metacarpal region flexor tendons of horses. The data on the CSAs of the SDFT, DDFT and AL-DDFT in WB, QH and SBs provides additional physiological references for these breeds to compliment the CSA data previously published for other breeds.