Stress in the Racing Horse: Coping vs Not Coping

Parasympathetic tone activity, heart rate, and grimace scale in conscious horses of 3 breeds before, during, and after nociceptive mechanical stimulation

BACKGROUND

Parasympathetic tone activity (PTA) in response to nociceptive stimulus in conscious non-sedated horses is unknown.

OBJECTIVES

Study PTA, heart rate (HR), and horse grimace scale (HGS) at rest and during mechanical nociceptive stimulation.

ANIMALS

Ninety healthy young adult horses (females, males): 30 each of Friesians, Quarter Horses, and Warmbloods.

METHODS

Prospective control study. The study consisted of habituation to equipment (Day 1), baseline recordings (Days 2 and 3), and nociceptive testing applying mild pressure to the metacarpus (Day 4). Parasympathetic tone, HR, and HGS were recorded simultaneously on Days 2 to 4. Each study lasted 30 minutes and was done in triplicate at 3 different time points per day.

RESULTS

Baseline PTA was not different among breeds. It decreased in Warmbloods and Quarter Horses during placement of the stimulus device without stimulation (P < .01). A significant decrease in PTA (P < .001) occurred during nociceptive stimulus (marked in Quarter Horses, intermediate in Warmbloods, and mild in Friesians). Heart rate and HGS increased significantly (P < .001) during the stimulus in all breeds but returned to baseline poststimulation. Friesians required higher pressure (P < .05) to elicit an aversive response to the stimulus.

CONCLUSIONS

Horses' PTA, HR, and HGS change in response to a mild mechanical nociceptive stimulus with Friesians showing less variation. Stress induced a decrease in PTA in Quarter Horses and Warmbloods but not in Friesians. Friesians appeared to be more tolerant to pain based on PTA, HR, and HGS findings compared with other breeds.

The Oxidative Stress Markers of Horses-the Comparison with Other Animals and the Influence of Exercise and Disease

Diacron-reactive oxygen metabolite (d-ROM) and biological antioxidant potential (BAP) levels in the serum of horses were measured (ponies, n = 15; thoroughbred, n = 31; other full-sized horses, n = 7). The mean d-ROM levels in horses were significantly higher (p < 0.001) than those in dairy cattle (n = 25) and dogs (n = 31). However, d-ROM levels in horses were lower than the standard levels reported in humans. When d-ROM and BAP levels were plotted graphically, the points for horses with a disease (ringbone in 1 Japanese sports horse, cellulitis in 1 thoroughbred, melanoma in 1 Lipizzaner) fell outside the group of points for other (non-diseased) horses. A similar separation was seen (using data from other authors) for a horse with Rhodococcus equi, a horse following castration surgery, and a mare following delivery. These results, comparing horses, other animals, and humans, are interesting from the standpoint of comparative medicine, and they contribute to the sparse literature available on d-ROM and BAP levels in animals. Because the level of d-ROM and BAP levels were changed depending on the situation of health, those indexes are promising as indices of health in horses.

Telomere regulation: lessons learnt from mice and men, potential opportunities in horses

Telomeres are genetically conserved nucleoprotein complexes located at the ends of chromosomes that preserve genomic stability. In large mammals, somatic cell telomeres shorten with age, owing to the end replication problem and lack of telomere-lengthening events (e.g. telomerase and ALT activity). Therefore, telomere length reflects cellular replicative reserve and mitotic potential. Environmental insults can accelerate telomere attrition in response to cell division and DNA damage. As such, telomere shortening is considered one of the major hallmarks of ageing. Much effort has been dedicated to understanding the environmental perturbations that accelerate telomere attrition and therapeutic strategies to preserve or extend telomeres. As telomere dynamics seem to reflect cumulative cellular stress, telomere length could serve as a biomarker of animal welfare. The assessment of telomere dynamics (i.e. rate of shortening) in conjunction with telomere-regulating genes and telomerase activity in racehorses could monitor long-term animal health, yet it could also provide some unique opportunities to address particular limitations with the use of other animal models in telomere research. Considering the ongoing efforts to optimise the health and welfare of equine athletes, the purpose of this review is to discuss the potential utility of assessing telomere length in Thoroughbred racehorses. A brief review of telomere biology in large and small mammals will be provided, followed by discussion on the biological implications of telomere length and environmental (e.g. lifestyle) factors that accelerate or attenuate telomere attrition. Finally, the utility of quantifying telomere dynamics in horses will be offered with directions for future research.

Influence of Horse and Rider on Stress during Horse-riding Lesson Program

The present study aims to confirm the influence of a horse-riding lesson program (HRLP) on the stress level of horses and riders by respectively analyzing their salivary cortisol concentration. Twenty-four healthy horses and 23 riders participated in this study. The horses were randomly classified into two groups for the horse riding lesson program: Class 1 (for the beginner lesson) and Class 2 (for the intermediate lesson). The Class 1 group consisted of 12 horses and 12 riders, while the Class 2 group consisted of 12 horses and 11 riders. Salivettes cotton wool swabs were used for saliva collection and the saliva analyses were conducted using a two-way analysis of variance for repeated measures with SAS version 8. As for the results, the average salivary cortisol concentration of all horses before HRLP significantly increased compared to the baseline (p<0.001) while it decreased after the HRLP. The results of the salivary cortisol concentration of the riders were similar to the horses’ results. However, there was no difference during the HRLP between Class 1 and Class 2 in the horse or rider groups. The results suggest that the HRLP did not influence the stress level of the horses or riders. Thus, this study provides the necessary information and guidelines for future studies on stress in horses during riding and gives insight into better horse welfare and management options.