Tying Up

Symptoms may include weakness, gait abnormalities, lack of energy or rapidly developing fatigue, reluctance to move forward, stopping to stretch out as though needing to urinate, muscle pain, muscle cramping and muscle cell damage (exertional rhabdomyolysis, more commonly known as tying up), and progressive atrophy. Symptoms range from so subtle that they go unnoticed to so cripplingly painful that the horse cannot work at all. The prevalence of PSSM exhibits a range across breeds: Percherons – 54%; North American Belgians – 36%; Warmbloods – 18%; Quarter Horses – 6-10%; Appaloosas and Paints – 6-8%. The syndrome may manifest differently across breeds with quarter horses more likely to tie up, drafts more likely to exhibit weakness, and warmbloods more likely to exhibit back pain and abnormalities of gait.

The keys to managing a PSSM horse are ensuring that dietary hydrolyzable carbohydrate (starch plus ethanol soluble carbohydrates or ESC) content is low and that extra calories, if needed, are supplied using a moderate amount of fats. Environmental management is critical; PSSM horses need regular exercise (daily is ideal) and as much turnout as possible to maximize time moving. Living on a track system that encourages constant movement is extremely beneficial. Exercise and constant movement in the environment improve the utilization of glycogen (reducing the probability of tying up) as well as the ability to use fat as an energy source (improving muscle strength and endurance).

Mooney is a 17 year old Belgian/Quarter horse cross diagnosed with PSSM1 in 2022. For several years he was well-managed with diet and regular exercise but in early summer 2024 he started to tie up again and his symptoms became extreme – he was unable to trot or canter without becoming anxious, stiff, sweating profusely, and experiencing painful muscle spasms most obvious in his neck.

Mooney is a vaulting horse. Vaulting is an ancient equestrian discipline that traces its lineage back to the Roman Empire — think acrobatics on horseback (for vaulting at the World Cup level — see here: https://www.youtube.com/watch?v=VaNG8Ox_Saw). In order to do his job, he has to be able to canter rhythmically in a circle without any alteration in stride length or pace so that his vaulter can time her acrobatics to the motion of his back. Tying up meant that Mooney could not do his job. His owner reached out for a consult.

Although Mooney’s diet consisted of appropriately low hydrolyzable carbohydrates and some fats, the foods constituting his diet were problematic, his key vitamin and mineral levels were inadequate, and he lacked adequate antioxidants. The fat source was extremely high in systemic inflammation-promoting omega-6 fatty acids.

Mooney’s diet was changed to include unprocessed foods low in hydrolyzable carbohydrates and multiple anti-inflammatory fat sources. His history suggested an underlying gut irritation; several levels of gut support were begun. Supplements to control inflammation, to provide antioxidants for muscle protection and repair, to support muscular relaxation, and to divert glucose away from excess glycogen deposition in the muscles also were begun.

Mooney’s protocol was implemented by the end of September. The first week of October his caretaker reported that he was already much more relaxed. By the third week of October he could cavort happily in the round pen without any signs of stress or imminent tying up. In November he did his first vaulting class since June – cantering effortlessly and happily while his young vaulter practiced on his steady, rhythmic back.

A joyful outcome for everyone!

How was this resolution accomplished? By taking what is known about the pathophysiology of PSSM1 and using nutritional tools to offset those abnormalities.

Result: a happy gelding who can do his job without anxiety and pain.

Have a complicated or difficult-to-manage horse? Message or go to https://4oaksequine.com

References:

McCue et al. Estimated prevalence of the Type 1 Polysaccharide Storage Myopathy mutation in selected North American and European breeds. Animal Genetics. 2010. 41 Suppl 2; 145-149

McCue and Valberg. Estimated prevalence of polysaccharide storage myopathy among overtly healthy Quarter Horses in the United States. Journal of the American Veterinary Medical Association. 2007; 231(5); 746-750

Firshman et al. Epidemiologic characteristics and management of polysaccharide storage myopathy in Quarter Horses. American Journal of Veterinary Research. 2003; 64(10); 1319-1327

Hunt et al. An epidemiological study of myopathies in Warmblood horses. Equine Veterinary Journal. 2008; 40(2); 171-177

McCue et al. Prevalence of polysaccharide storage myopathy in horses with neuromuscular disorders. Equine Veterinary Journal. 2006; 36; 340-344.

For review: https://madbarn.com/type-1-pssm-in-horses/

For technical review of pathology: https://vetmed.umn.edu/…/polysaccharide-storage…