Excessive drowsiness secondary to recumbent sleep deprivation in two horses.

This research article examines two cases of horses displaying excessive drowsiness due to recumbent sleep deprivation. Both cases presented distinctive symptoms, and through a series of clinical examinations and treatments, the study concluded that sleep deprivation in horses should be properly diagnosed to avoid mislabeling it as narcolepsy-cataplexy or equine protozoal myeloencephalitis.

Case I

Case I involves a 12-year-old Quarter Horse gelding that had lost a significant amount of weight, with no other noticeable clinical signs.

• After thorough screenings and examinations, an interesting phenomenon was observed – whenever the horse was left to rest in his quiet stall, he would show signs of falling asleep but would start to collapse just as his head got close to the ground. This phenomenon was attributed to his inability to sleep in a recumbent (lying down) position.
• The diagnosis included a number of factors such as chronic peritonitis, adhesions, and enteroliths, but the core cause of the weight loss was linked to a lack of recumbent sleep.
• Treatment involved surgery to deal with the enteroliths and other abdominal issues. Within an hour of surgery, the horse was seen lying down for the first time since arriving at the clinic. This amounted to nearly 12 hours of rest and led to a significant improvement in the horse’s health and weight.

Case II

Case II concerned an 8-year-old Quarter Horse gelding that had been constantly collapsing for about 8 months. He had been referred for supposed narcolepsy-cataplexy secondary to equine protozoal myeloencephalitis.

• Despite testing positive for Sarcocystis neurona, the assumed cause of his recurring collapse, treatment with antiprotozoal medication showed no improvement in his condition.
• The horse was comfortably housed in a 10-acre field but was the only horse present. This isolation led the researcher to believe that social isolation, rather than illness, might have been the cause of sleep deprivation, as horses are herd animals.
• A second horse was introduced to provide the gelding with a companion, and this greatly reduced the collapsing episodes. After catching up on lost sleep, the gelding returned to a state of normalcy.

Discussion and Conclusion

The author concluded that these case studies underscore the importance of properly diagnosing recumbent sleep deprivation in horses. The underlying causes—pain and environmental insecurity—came as a surprise as neither horse suffered from narcolepsy-cataplexy, equine protozoal myeloencephalitis, or any known central nervous system disorder. Mislabeling can lead to incorrect treatment and further health consequences.