SAEVA Proceedings 2016 | Page 31

  sand is firm closer to the waves. The impact of transporting the horses was an interesting factor and again not unexpected. It has been shown that horses dehydrate when transported and are more stressed (Stull et al and Yanez-Pizana et al) and both these factors are going to result in an increase in the core temperature of exercising horses. The decreased prevalence of PRDS when horses race at night was the same as in the previous paper when looking at the races at the Newmarket racecourse. This can be attributed to the cooler temperatures experienced at night. However, in November 2009 the lights were moved to the Turffontein race course. At this course, there was no decrease in the prevalence when racing after 18h00, but this can be attributed to the smaller numbers of runners so far, as well as one particular horse that shows PRDS virtually every time he races. As time goes on and the numbers increase, it is expected that the prevalence of PRDS at night at this track will decrease. It was interesting to note that the fitting of blinkers is now shown to be not significant. This is in contradiction to the previous paper, but the increased number of cases means that this finding is more reliable. The most startling result was that of horses that have some form of respiratory stridor being approximately 13 times more likely to show PRDS. This has to be related to the marked nasal cooling that occurs in the horse due to its high ratio of upper respiratory tract surface area to brain mass (McConaghy et al.1995). Any restriction in air flow must affect this, leading to increased cerebral hyperthermia. The acute hind limb discomfort exhibited by some horses may be ascribed to the rerouting of blood supply to the skin and respiratory tract away from the muscles when the horse becomes hyperthermic (McConaghy et al. 2002). The resultant hypoxia to the muscles could result in the symptoms experienced. The importance of environmental factors and the various risk factors that have been identified shows that it may be possible to predict which horses are likely to show PRDS. This could help in the management of the syndrome leading to a reduction in its prevalence. REFERENCES 1. MacDonald DM, Wheeler DP, Guthrie AJ, Kok C, Pilgrim T. ‘Post Race Distress Syndrome’ in Thoroughbred Racing in South th Africa. Proceedings of the 17 International Conference of Racing Analysts and Veterinarians, Antalya, Turkey, 2008. 2. McCutcheon, L. Jill and Geor, Raymond J. "Thermoregulation and Exercise-associated Heat Illnesses” in "Equine Sports Medicine and Surgery: Basic and Clinical Sciences of the Equine Athlete. By Kenneth W. Hinchcliff, Andris J. Kaneps, and Raymond J. Geor. Edinburgh: Saunders, 2004: 919-933. 3. McConaghy FF, Hales JRS, Rose RJ, et al. Selective brain cooling in the horse during exercise and environmental heat stress. J Appl Physiol 1995; 79: 1849-1854. 4. Hodgson DR, McCutcheon LJ, Byrd SK, et al. Dissipation of metabolic heat in the horse during exercise. J Appl Physiol 1993; 74: 1161-1170. 5. McConaghy FF, Hodgson DR, Hales JR, et al. Thermoregulatory-induced compromise of muscle blood flow in ponies during intense exercise in the heat: a contributor to the onset of fatigue? Equine Vet J Suppl 2002; 34: 491-495. 6. Nielsen B, Savard G, Richter EA, et al. Muscle blood flow and muscle metabolism during exercise and heat stress. J Appl Physiol 1990; 69: 1040-1046. 7. Kohn CW, Hinchcliff KW, McKeever KH. Evaluation of washing with cold water to facilitate heat dissipation in horses exercised in hot, humid conditions. Am J Vet Res 1999; 60(3): 299-305. 8. Stull CL and Rodiek AV. Physiological responses of horses to 24 hours of transportation using a commercial van during summer conditions. J Anim Sci 2000; 78: 1458-1466. 9. Yanez-Pizana A, Roldan-Santiago P, Mora-Medina P, et al. Effects of transport on the metabolism of horses. Rev Cient 2012; XXII (5): 432-436. Proceedings  of  the  South  African  Equine  Veterinary  Association  Congress  2016   30