Evaluation of Heart Rate as Marker of Stress during Road Transport in Horses

Background: Nowadays horse transportation represents an increasingly practice as a greater number of horses are subjected to transport for several purpose including sport competitions, breeding and selling. In the past, horses were usually transported by train and ship however, at the present time, they move mainly by road with trailers or vans. Transport represents a potential stressor that might compromise horse performance therefore, the chance to monitor horse welfare during transportation is of great interest. The autonomic nervous system and its regulation of cardiovascular function have been considered suitable indicators of stress and welfare in humans and animals. Measuring the vagal tone provide a best knowledge about stress vulnerability and the magnitude of a stress response. Considering that heart rate (HR) represents the effect of the vagus, the aim of this study was to evaluate if this parameter is an affordable indicator of stress in horses subjected to different experimental conditions concerning the duration and the time of the day of road transportation. Materials, Methods & Results: Twelve clinically healthy athletic Italian Saddle horses, divided into three equal groups, were transported over two different distances (110 Km and 225 Km) at the same time of the day (5.00 pm) (group A and B), and over the same distance (110 Km) during the evening (5.00 pm) and during the morning (8.00 am) (group A and C). Each journey was divided into 3 parts (T1, T2, T3) on the basis of road characteristics: T1 and T3 periods represented the time spent travelling on secondary roads characterized by several changes of direction and average speed of 35-40 Km/h; T2 was travel duration on nearly completely rectilinear motorways with average speed of 70 Km/h. Mean HR recorded at rest for each horse was 38 +/- 3 beats/min. On HR values recorded during transportation one-way ANOVA showed significant statistical differences of HR values in T2 vs T1 and T3 periods within the group A (P < 0.0001) and C (P = 0.003); no significant statistical difference was found in T1, T2 and T3 periods within group B. T tests showed that mean HR values were lower in group B than in group A, and higher in group C than group A only in T2. Discussion: Even if transport includes a series of potential stressors such as handling, loading, unloading, unfamiliar environments, oscillation and vibration of the mean of transport, noise, social regrouping, poor ventilation, deprivation of both food and water; in the present study our recordings showed that HR changed irrespective of the experimental characteristics of the journey including the different duration of each transportation. We found that neither the average speed of the mean of transport or the characteristics of the road determined significant changes in horse HR. We also found no influence of the time of the day on HR trend during transportation in horses. This might be due to the fact that HR varied when posture and other external stimuli changed during transport masking the biological rhythms that usually affect the cardiovascular activity and the HR diurnal variability that suits the needs of different levels of activity at different time of the day. On the basis of these results, HR seemed to be an extremely variable parameter profoundly affected by the temporary responses of the horses to sudden environmental incidents.