Q. My husband and I have raised several hundred horses over the last 40 years, but we have never seen an issue like the one affecting my 4-year-old Quarter Horse gelding. He does not like to bend his knees and hocks. When I ride him, he feels like he is walking on stilts. He does not like to go downhill and seems most comfortable at a slow lope.

I had a vet check him out. He is not really lame, has no lumps or bumps, no sign of strains, etc., and he did fine on a flexion test. The vet said he would pass a pre-sale vet check. He has only had very light riding all his life and shows no sign of joint damage. We raised him and own his sire and dam and also his grandparents. All were very athletic and none had problems in their knees or hocks. 

The horse gets worse when I feed him alfalfa and is markedly better when he is on grass hay. I read something about some horses being allergic to certain plant hormones in fresh hay, and I am beginning to suspect he might be allergic to the proteins in alfalfa. Is this possible? What might be going on here?

Larryann Willis, via e-mail

A. These signs could have several different causes, and a closer look at his history coupled with further veterinary examination should get you closer to a diagnosis. Has he had any other unrelated illness in his past? Has he been tested for hyperkalemic periodic paralysis (HYPP)? Can his joints be fully flexed without resistance? Has he always done this or did it come on suddenly, and does it get worse over time or stay the same? Answers to these questions will better direct your veterinarian as to which diagnostic tools to use.

The link between feeding alfalfa and the onset of clinical signs is interesting, and, if accurate, could point to several conditions: The higher protein and energy content of alfalfa compared to grass hay could predispose a Quarter Horse to episodes of tying-up or recurrent exertional rhabdomyolysis. Also, the concentration of estrogens in clover-based hays is higher than grass hays and is thought to possibly have an adverse effect on the ligamentous structures of the limbs, but this observation is unproven.

True allergies, or hypersensitivity, to allergens in the alfalfa have not been reported. A study on horses with chronic laminitis did, however, demonstrate a hypersensitivity response, while another report documented polysynovitis (inflammation of multiple joints) of unknown cause in three horses. Such case reports show it might be possible that a hypersensitivity reaction is at play, although a respiratory component would typically be expected.

A form of immune-mediated polysynovitis, similar to rheumatoid arthritis in humans, could be another possible, but rare, cause of the signs noted, although swollen and/or hot joints would usually accompany the other signs. It might also be possible that another condition, such as early-onset polyarthritis (osteoarthritis), could be present. This has many potential causes, but radiographs of the suspected joints should yield a diagnosis.

Chronic laminitis should also be investigated as a possible cause, as many horses will show worsening of signs on richer forage such as alfalfa.

You also mention he resists traveling down hills and travels best at a slow lope. This could be a manifestation of pain in his limbs, but it could also be an expression of an underlying neurological problem.

This would be more unusual, but horses with some component of liver failure show worsening of signs when fed high-protein diets such as alfalfa, and this, if mild, could potentially manifest only as incoordination or clumsiness.

A full neurological and lameness examination should be performed, including evaluation at a slow walk and in tight circles to pinpoint the origin of his unusual gait.

About the Author

Jonathan McLellan, BVMS (hons), MRCVS

Jonathan McLellan, BVMS (hons), MRCVS, is a practitioner with Ferguson, Hammock, and BonenClark Equine Hospital in Ocala, Fla.

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