The effect of rider weight and additional weight in Icelandic horses in tölt: part I. Physiological responses.

This study aimed to understand how increasing the body weight ratio (BWR) between a rider and an Icelandic horse affects the animal’s physiological responses. The research concluded that as BWR increases, the horse’s heart rate, plasma lactate concentration, body temperature, and breathing frequency also increase, indicating a greater degree of physical stress.

Research Methodology

• The study involved eight experienced school-horses undergoing an incremental exercise test performed on an outdoor oval riding track. A single rider rode all the horses to maintain control and consistency.
• The exercise test had five phases where the body weight ratio (BWR) between the rider (including the saddle) and the horse initially started at 20% and was increased in increments up to 35%. After reaching 35%, it was decreased back to 20%.
• After each phase, the horses were briefly stopped to add lead weights to the rider’s specially adjusted saddle bags and vest to increase the BWR.
• During the warm-up, the exercise test, and the recovery periods, the researchers measured the horses’ heart rate, and took samples to ascertain their plasma lactate concentration and breathing frequency.
• Rectal temperature was also measured before and after the exercise, and after a 30-minute recovery period.
• The researchers also noted body size, body condition score and performed clinical examinations before and after the test.

Findings and Conclusion

• As BWR increased, the heart rate, plasma lactate concentration (an indicator of stress and fatigue), body temperature, and breathing frequency of the horses also increased. This pointed towards increased physical strain on the horses with increased BWR.
• While the heart rate, hematocrit (ratio of red blood cells to total volume of blood), and breathing frequency recovered to their normal levels within 30 minutes of the exercise, the plasma lactate concentration and rectal temperatures did not, pointing to prolonged physiological effects of increased BWR.
• Interestingly, the study found individual differences among horses, meaning that the percent of BWR at which horses began to work aerobically (using oxygen to meet energy demands) varied between 17% and 27.5%. This variance was not linked to the horse’s size, but to its body condition score (an assessment of fat coverage on a horse’s body).
• The study thus concluded that increasing the BWR from 20% to 35% indeed led to significant physiological changes in the robust Icelandic horses.