We develop the knowledge about the response to exercise in Icelandic horses. An important contribution for the understanding are the studies performed during the PhD education of Guðrún Stefánsdóttir. We have also started a new PhD project where we will further investigate the weight carrying capacity of the horse. The PhD student is Denise Söderroos.
This thesis examined the exercise physiology of the Icelandic horse by: 1) studying physiological response in stallions and mares of different ages performing a true breed evaluation field test (BEFT); 2) comparing the effect of ridden tölt and trot at three speeds on physiological response; 3) evaluating physiological response to a simulated 100 m flying pace race; 4) measuring the effect of increasing body weight ratio (BWR) of rider to horse (20, 25, 30, and 35 %) on physiological response in an standardised incremental field exercise test at tölt at 5.4 m/s; and 5) determining the effect of rider on physiological response. In all studies, speed, distance, heart rate and breathing frequency were recorded and plasma lactate concentration, haematocrit and rectal temperature were measured before and after the exercise tests.
The main results of this thesis were that Icelandic horses performed high intensity exercise during the true gait tests (BEFT and pace race) and, depending on the weight of the rider, the horses at the medium speed tölt and trot (~5.5 m/s) typical of leisure horses also temporarily performed high intensity exercise. Anaerobic metabolism was crucial for performance at pace. Aerobic fitness was higher in stallions than in mares and age had a limited effect on the physiological response in BEFT, although 4-year-old horses had lower aerobic capacity than older age groups. Peak heart rate decreased with age. There were only minor differences in physiological response to tölt and trot in a group of experienced adult Icelandic horses. There was an effect of rider, with physiological response increasing with increased BWR of rider to horse. Trained and experienced Icelandic horses may exceed their lactate threshold at medium speed (~5.5 m/s) at BWR common for Icelandic horse-rider combinations. Post exercise plasma lactate concentrations were correlated with recovery heart rate. Thus by recording recovery heart rate, trainers of Icelandic horses can get an estimate of post exercise plasma lactate concentration, which reflects the extent of anaerobic metabolism and workload. Overall, the results suggest that training of aerobic and anaerobic metabolism is important for BEFT performance and that training of anaerobic metabolism is of critical importance for pace performance
Doctoral Thesis - Physiological response to exercise in the Icelandic horse