Question: In “Exercise and Arthritis” (Consultants, EQUUS 464) a letter from a reader solicited advice for managing her arthritic horse; the letter writer stated that the horse in question was also prone to laminitis. The horse was already receiving an MSM/glucosamine supplement, and Roland Thaler, VMD, the consulting veterinarian who answered the question, also referenced glucosamine-containing supplements, among others, to help horses with arthritis.

Because this reader’s question pertained to an older, laminitis-prone horse, it’s likely that he could be insulin resistant. I was under the impression that supplementation with glucosamine should be avoided since it could exacerbate the laminitis. Glucosamine is a sugar and has been used in laboratory settings and animal studies to induce insulin resistance to study the condition. It is my understanding that donkeys should not be supplemented with glucosamine under any circumstance.

As we all know, a laminitis flare-up can be career-ending, life-altering or worse. I wouldn’t know myself if I hadn’t lived it.

L. Diane Stowe Heath, Massachusetts Answer:

Let me sincerely commend you for your concern about the welfare of horses. Preventing laminitis is a desire we all share. But I would like to address several points.

First, glucosamine is not a pure sugar, like glucose, fructose and others. It is an amino sugar, which is a sugar combined with a nitrogen compound called an amine, and it is manufactured in all of our bodies to sustain the processes of life. While the metabolic pathways of glucose and glucosamine are somewhat closely related, they are distinct.

Most studies have shown that glucosamine supplements do not affect glucose metabolism at the sustained daily dosages typically used by people. So, in general terms, glucosamine is deemed safe for human supplementation, even for people with diabetes. Additional studies on the effects of glucosamine on the metabolism in other mammal species have yielded the same conclusion. In studies meant to induce insulin resistance in laboratory animals, the levels given are 100 times the normal dosage, which can lead to a competitive effect on uptake within the cell and may cause elevated serum glucose. However, the supplementation dosage for horses does not nearly approach these levels.

Second, after searching the PubMed database for scientific papers, I could find no peer-reviewed references to the effects of glucosamine supplementation on glucose/insulin metabolism or laminitis. Searching the Internet does bring up many posts that raise this question as a possible concern, but I was unable to verify any of the sources. Additionally, I was unable to find any specific scientific evidence that donkeys are especially sensitive to glucosamine administration. From a literature standpoint, glucosamine supplementation appears to be safe for all horses.

In summary, feed supplements are not a substitute for good veterinary care. If a horse is moving stiffly, it is important to identify the underlying cause before attempting any treatment, including supplementation. If the horse is developing laminitis, then the case needs to be diagnosed and treated appropriately.

Roland Thaler, VMD, DACVSMR, Cert. ISELP, Cert. COAC Metamora Equine Clinic PC Metamora, Michigan

This month’s expert: Roland Thaler, VMD, owns the ambulatory equine practice Metamora Equine Clinic PC. He is a member of the International Society of Equine Locomotor Pathology, American Association of Equine Practitioners, American Veterinary Medical Association and the Michigan Horseshoers Association. Thaler earned his veterinary degree at the University of Pennsylvania and interned at the Delaware Equine Center in Cochranville, Pennsylvania.

This article first appeared in EQUUS issue #469, October 2016.