Effect of increasing work rate on metabolic responses of the donkey (Equus asinus).

This study investigates how increasing work rate impacts the metabolic responses in donkeys, focusing on oxygen consumption and the concentration of metabolites in venous blood. The test subjects were trained to run and pull loads on a treadmill, with the researchers tracking changes in heart rate, blood lactate levels, and blood glucose levels.

Methodology and Experimental Conditions

• Donkeys were conditioned to perform two activities for the experiment: running at maximum speed on a treadmill with a 9.8% slope and walking on a level surface with incremental loads.
• Oxygen consumption (VO2), heart rate, and levels of certain venous blood metabolites (blood lactate and glucose) were measured.
• The total energy cost of a donkey walking unloaded was calculated and used as a baseline.
• Changes in these metrics were monitored during low to medium-intensity draft work carried out for 25 minutes.

Key Findings

• The study found that during maximal speed running on a 9.8% slope, the VO2 of the donkeys was around 22 times higher than the preexercise VO2.
• The average heart rate at maximum VO2 (indicative of maximum physical exertion) was approximately five times the pre-exercise rate.
• Blood lactate increased 14-fold under these conditions, whilst blood glucose did not show significant changes. Blood lactate is a metabolite produced by muscles during intense physical activity and is a marker of anaerobic metabolism.
• However, during low to medium-intensity draft work, blood glucose fell below preexercise values, while plasma hematocrit and cortisol levels increased. Blood lactate remained unchanged until reaching approximately 40% of the VO2 max, but increased significantly at around 60% of the VO2 max.
• The findings suggest that donkeys show similar metabolic responses to horses during exercise, with the exception of lower lactate levels at high-intensity exercise and the observed rapid decline in blood glucose during low-intensity exercise.
• The findings also suggest that the metabolic changes observed are a result of the body’s response to the increased demand for energy during exercise, including elevated heart rate, increased VO2 (oxygen consumption), and changes in blood lactate and glucose levels.