Physiological response to weight carrying and associations with conformation traits in Icelandic horses used for tour riding.

BACKGROUND

Weight carrying capacity is an important trait in riding horses and it may be associated with conformation. This study examined the physiological response to a ridden incremental weight carrying test in 16 adult Icelandic horses used for tour riding. Horses carried 20% (BWR), 25% (BWR), 30% (BWR) and 35% (BWR) of their body weight (BW) in tölt (~ 5.7 m/seconds, 640 m/step), and associations with body measurements and back conformation (score) were examined. Horses were divided into two groups (narrow or broad back) and body measurements were collected. Plasma lactate was analysed in blood samples collected after each step in the exercise test, an exponential equation was fitted, and BW-ratio was calculated for 2, 3 and 4 mmol/L (BWR, BWR and BWR). Plasma creatine kinase (CK) and aspartate amino transferase (AST) were analysed at rest and 24 h post exercise.

RESULTS

Four out of 15 horses did not reach a plasma lactate concentration of 4 mmol/L, even at BWR. A positive correlation was found between chest width and BWR and between the difference between height at withers and croup and BWR (P < 0.05). Hock circumference and the difference between height at croup and back were negatively correlated with BWR (P < 0.05). The change in CK from rest to 24 h post exercise was negatively correlated with the difference between height at withers and height at back and croup (P < 0.05).

CONCLUSIONS

The physiological response to weight carrying was relatively low. A wider chest, "uphill" conformation, straight backline and smaller hock circumference were associated with weight carrying capacity, but group (narrow or broad back) was not.