Effects of caffeine on locomotor activity of horses: determination of the no-effect threshold.

This research explored the effects of caffeine on the locomotor activity of race horses, identifying the maximum dose that has no impact on the animals’ spontaneous movement. The study found that dosages of caffeine above 2.0 mg/kg increase spontaneous locomotion, and suggests that permissible caffeine levels in plasma and urine should not exceed 2.0 microg/ml and 5.0 microg/ml respectively.

Experimental Setup

• The researchers conducted the study in two specially designed behaviour stalls. Each stall was partitioned into nine segments using infrared beams. When a horse interrupted a beam with its leg, the interruption was recorded, allowing for the quantification of movement.
• In order to limit external influences on the horses’ movement, the setup included exhaust fans producing white noise to mask other sounds, and one-way observation windows to prevent the animals from viewing the outside world.

Data Collection

• For 45 minutes before administering a dose of caffeine, the researchers monitored the horses’ spontaneous locomotor activity as a baseline measurement.
• Each horse was then given an intravenous dose of one of four caffeine concentrations. The doses varied between 2.0 and 5.0 mg of caffeine per kg of body weight. The movement activity was observed and recorded for eight hours post-administration.
• The team also collected urine and plasma samples from the horses for concentration analysis of caffeine. This was performed using gradient High-Performance Liquid Chromatography (HPLC) with UV detection.

Findings

• The research determined that a dose of 2.0 mg of caffeine per kg of body weight was the Highest No-Effect Dose (HNED) on spontaneous locomotor activity in horses. Any dosage above this threshold stimulated activity.
• From the sample testing, the researchers proposed that the no-effect threshold for caffeine should not exceed 2.0 microg/ml in plasma and should not exceed 5.0 microg/ml in urine.