It’s had many names–from azoturia to Monday morning sickness, but, despite the disease being well-recognized for hundreds of years, the causes of the equine muscle disorder most commonly known as tying up, have been elusive. Stephanie Valberg, DVM, PhD, Dipl. ACVIM, Dipl. ACVSMR, explained the history of this disease from ancient cart horses to modern genetic testing and took the audience at the Frank J. Milne lecture at the AAEP Convention into the current understanding of equine myopathies.


This mare from the University of Minnesota Equine Center’s PSSM herd is experiencing a tying-up episode with associated muscle stiffness, profuse sweating, and a reluctance to move.
Image courtesy of Dr. Stephanie Valberg

All horse people know the signs, even if we haven’t seen a horse in the act of “tying up,” we know to look for the muscle tremors, the shivering, the firm muscles. Nowadays, we even know to be on the lookout for more subtle signs such as reluctance to move forward, a stilted gait, or exercise intolerance. But there is still a lot of misunderstanding as to the causes and management of the conditions that result in “tying up.”

Yep, conditions. As Dr. Valberg said in the conclusion of her presentation, “Tying up” is not one specific disease. It’s a clinical term, like “colic” covering multiple