Gait, estimated net cost of transport and heat production at different speeds in three-day-event horses.

The research discusses an investigation into the gait, estimated energy expenditure and heat production in horses during a standardized exercise test and a three-day steeplechase event. The study employed heart rate and stride analyses to provide insight into the efficiency of the horses at different speeds and exercise intensities.

Objectives and Methodology

• The study was conducted on six horses that were subjected to a standard incremental exercise test where they moved in a trot and at increasing speeds up to a fast gallop. The test was performed under hot conditions, and the horses were observed during the steeplechase phase of a three-day event as well.
• The researchers used a unique scaling method based on the horses’ hind leg length, stride length and frequency, and speed. This was done to establish non-dimensional stride length, stride frequency, and velocity. It helped assess any significant differences in these characteristics over the full range studied.

Findings and Analysis

• No major differences were found in stride length or stride frequency characteristics. However, subtle differences in some horses were observed that indicated a potential advantage in locomotory efficiency compared to others performing at the same absolute speed.
• The relationship between stride length and frequency changed with increasing speed, transitioning from trot to canter and then to a full gallop. The transition from canter to gallop occurred when the non-dimensional stride length was approximately 3.2.
• The cost of transport per kg/m, calculated from the heart rates measured continuously during the study, was found to decrease with increasing speed and bodyweight. In some animals, a slight minimum was observed around the canter-gallop transition speed.
• When analysed in terms of oxygen cost based on the oxygen consumption-heart rate relationship from previous studies, the cost fell from an average of 0.201 ml/kg/m at the trot to 0.161 mlO2/kg/m when galloping during the incremental exercise tests.

Steeplechase Observations

• During the steeplechase event, the cost of transport was approximately 7.5% higher than at the same speed in the separate exercise tests. It was suggested that this could be due to the increased effort required for jumping.
• Power consumption increased linearly with speed and was found to be 7.5% higher during the steeplechase, compared to the same absolute speed in the exercise tests. This equated to an average rate of heat production of 346 kcal/min (24kW), or 59.5 kcal/min/m2 of the measured body surface area of the horses.