The Horse:Your Guide To Equine Health Care provides monthly equine health care information to horse owners, breeders, veterinarians, barn/farm managers, trainer/riding instructors, and others involved in the hands-on care of the horse.
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24 TheHorse.com THE HORSE October 2015 of oral stereotypies or other abnormal behaviors, along with gastric ulceration in horses. In broodmares, these stress- ful dietary restrictions can even impact reproductive efficiency. "It is well-known that horses are trickle feeders that would naturally consume a semicontinuous supply of forage for 40-70% of each 24-hour period," explains Martine Hausberger, PhD, director of the Laboratory of Animal and Human Ethology, a branch of the French national research center (CNRS) and the Uni- versity of Rennes. "It is also known that horses can experience gastrointestinal discomfort if deprived of food for a mere one to two hours." A good measure of stress in horses, which don't always reveal signs of GI discomfort, can be its effects on reproduc- tion. After feeding 100 Arabian brood- mares in either a standard pattern (fed forage only at night) or a continuous feed- ing group (fed forage morning and night), Hausberger et al. found that despite having been fed the same total amount of roughage, mares in the continuous feeding group had significantly fewer estrous abnormalities and an almost 30% higher conception rate than those in the standard group. These results suggest that stress related to noncontinuous feeding hinders reproductive performance. The study authors deduced that semi- continuous feeding of roughage might be a way to fulfill the basic physiological needs of the horses' digestive system, reduce stress, and promote reproductive success. Reproductive system stress Tom Stout, VetMB, PhD, an equine reproduc- tion researcher in Utrecht University's Department of Equine Sciences, in The Netherlands, says physiological stressors such as pain, systemic disease, weaning, transport, changes in group structure, poor nutrition, or temperature extremes can predispose mares to pregnancy loss. Even a mare's transrectal pregnancy check—using an ultrasound probe to "see" the uterus through the rectal wall—can cause significant stress. "Transrectal ultrasound examinations are standard for detecting ovulation and identifying pregnancy in horses," says Harald Sieme, DVM, DrMedVet, profes- sor of Equine Reproductive Medicine at the University of Veterinary Medicine in Hanover, Germany. Sieme and colleagues determined that conducting the exam in nonlacting pregnant mares caused "significant disruption of homeostasis and stress," evident from heart rate, heart rate variability, and saliva cortisol levels measurements in 25 mares. This was in line with previous research findings that rectal examinations can induce stress, potentially contributing to welfare issues and even pregnancy loss. Sieme and his colleagues determined that transabdominal ultrasound, which is performed through the abdominal wall (as in pregnant women) is a better approach for nonlacting pregnant mares after Day 90 of gestation. Says Stout, "Although the exact role of stress in pregnancy loss is not clear, it seems prudent to minimize stress during pregnancy." Gastrointestinal illness and colic Not surprisingly, colic is extremely stressful for both horse and owner. Researchers in the U.K. recently confirmed this by measuring heart rate and circulating cortisol levels in 179 referred colic cases and comparing them to 30 systemically healthy control horses. Horses with se- rum total cortisol concentrations (STCCs) above 200 nmol/L (nanomoles per liter) were more likely to colic than controls, and colicking horses with STCCs above 200 nmol/L were more likely to display moderate to severe colic signs (e.g., heart rate higher than 45 beats/min). The study authors concluded that STCCs might provide additional decision-making (e.g., whether to go to surgery) and prognostic information in horses with colic. "This study confirmed that horses with colic demonstrate elevations in STCCs and suggests that an increase in STCCs relates to the severity of the underlying disease," they wrote. Transport-related stress In a 2015 study, researchers found that fecal cortisol levels increased in 2-year-old Thoroughbreds after their transport and arrival at an auction in South Africa. Study authors suggested that this "reflect- ed a cumulative series of stressful events associated with transport and sales ar- rival." The levels decreased as the horses became accustomed to the environment and routine. The authors also noted that this physiological stress response and commingling might increase the risk of infectious upper respiratory disease de- veloping in young horses. They suggested further investigation into transport and arrival phases and management practices to improve horses' health and welfare during events such as sales. Exercise-related stress In a 2015 study, researchers from the University of Sas- sari, in Italy, collected and analyzed Learn to recognize your horse's stress-related behaviors, such as pawing, kicking, and fdgeting. PAULA DA SILVA ALL Wo u n d U p ?