Continuous tractive force measurement and performance evaluation in working horses - a pilot study

In both equestrian sports and alternative husbandry horses are more and more used as draft animal. Also in draft horses an efficient power transmission plays an important role in regard to the animal's wellbeing. The aim of the study was to classify the performance of working horses regarding their physical and psychological stress. Two defined traction forces (1300N and 2600N = target values) were continuously recorded during a load lasting for 30min each in two pairs of Freiberger horses each on the braked and loaded carriage. The tractive forces that were recorded corresponded to the actual values. The work performed by the horses was assessed. Heart rate was recorded using POLAR training watches (V800). To assess the workload including a possible psychological component, blood samples were additionally taken before, during, and after work (0, 15, 30, and 60 min) in which cortisol, glucose, and non-esterified fatty acids (NEFA) were determined. Data analysis was done in a descriptive and statistical manner (paired t-test, Pearson correlation coefficient, using the statistical program R, significance level was p<0.05). The average tensile forces were satisfactorily in accordance with the target values (1300N and 2600N, respectively): actual value pair 1/2: 1148N and 2543N, respectively, actual value pair 3/4: 1236N and 2538N, respectively. Traction forces and speeds resulted in traction powers of 813 and 2095 watts (1.11 and 2.85 horse power= hp) for each horse of pair 1/2 and 919 and 1934 watts (1.25 and 2.63 hp) for each horse of pair 3/4, respectively. Heart rates ranged from 94-124/min for both pairs at 1300N and 124-171/min at 2600N. Heart rates decreased by 50% 60sec after 15min of work at 1300N, and recovery times increased with longer and more intense work. At the tensile forces in the present work, glucose values of 4.79 mmol/l were measured on average for all horses at 1300N and values of 4.68 mmol/l were measured at 2600N. In the case of the older French mountain horse pair of carriage 3/4, an initial drop in blood glucose and a subsequent rise were more pronounced than in the French mountain horse pair of carriage 1/2. The older French mountain horses of carriage 3/4 were fed exclusively hay, while the horses of carriage 1/2 received an additional 2 kg of concentrates per day. The extent to which the low concentrate supplementation of the horses of the carriage 1/2 influenced the glucose metabolism remains speculative. The four French mountain horses achieved average NEFA values of 0.30 mmol/l at 1300N and 0.53 mmol/l at 2600N. At a traction level of 1300N, plasma cortisol levels for the four French mountain horses ranged from 29.3-50.3 ng/ml, and at the traction level of 2600N, plasma cortisol levels ranged from 24.8-58.8 ng/ml. In comparison, the values were higher in a previous study, where the average plasma cortisol values of nine Warmblood driving horses after 30-40 min of intensive training ranged from 60.72 +/- 9.51 to 63.66 10.07 ng/ml (Krumlych et al. 2018). Cortisol (nmol/l), glucose (mmol/l), and NEFA (mmol/l) values in the present study indicated moderate to heavy work intensities. Cortisol levels correlated significantly (p < 0.05) with heart rate (r = 0.64) and NEFA (r = 0.53), indicating balanced activation of the adrenergic system and hypothalamic-pituitary-adrenal (HPA) axis and suggesting a psychological stress component as unlikely.