From AAEP’s Ask the Vet: Could it be a Nutritional Deficiency?

I’ve done a lot of reading trying to figure out some issues with my horse. Is it possible for horses to be on a nice balanced diet of hay and pelleted feed and still have deficiencies? For example, my horse gets plenty of hay (as much as he is willing to eat) and the correct amount of high fat pelleted grain by weight daily yet is consistently underweight. He went from being fine about grooming to absolutely hating it over the last couple years. He dislikes being touched, having his blanket put on or removed, as well as anything other than the lightest leg pressure under saddle. He is otherwise quiet under saddle but has these freak outs on the ground where he gets nervous about something then literally starts shaking all over. I have treated him for ulcers a few times with no real results, although he has not been scoped. I’ve read about magnesium deficiency and wondered if that is possible or if it’s just another fad. There is a local place that does hair mineral testing, but I’ve been told almost all their tests come back with magnesium deficiency and aluminum toxicity. Is this a sign of a missing piece in most equine diets or just a game? I’ve also read that since magnesium gets low in the blood last that checking those levels is pointless. – Kristen

Dear Kristen,

And herein lies the difficulty with fortified grain. As you’ve already found out, the calories are tied to the other nutrients (protein, vitamins, minerals). You’ve weighed out the proper amount of grain to feed your horse based on his age, weight and workload, yet he’s too thin. In this case, your solutions are:
• Feed more of this particular grain, being careful not to give more than 0.5% body weight at any one meal (this may mean adding a third meal like a lunch)
• Gradually switch to a more calorie-dense fortified grain, where the recommended serving size has the same amount of protein, vitamins and minerals but more calories per pound
• Keep this grain but add another source of calories such as alfalfa cubes, beet pulp or rice bran
• Provide a weight gain supplement with calories coming from fat or fiber. Some products in this category also include amino acids like lysine, threonine and methionine to maintain a muscular topline.

And yes, it is entirely possible to provide your horse with the book—recommended levels of nutrients yet—as you’ve seen with calories and his weight—for him not to thrive at these levels. Remember, the NRC Nutrient Requirements of Horses suggests the minimum levels of calories, protein, fat, vitamins and minerals in order to prevent outright disease, not to optimize health and performance. In addition, horses are individuals and while the minimum level of a nutrient might be enough to allow one horse to say, grow healthy feet, this minimum level may not be enough for another horse. Differences in metabolism, digestive efficiency—even management and stress—can all factor in to why some horses thrive on a basic diet and others need additional support.

Your horse’s issues may or may not be nutrition-related. Either way, I encourage you to have your veterinarian out to examine him fully. Once you’ve ruled out physical causes for his change in behavior, at least you’ll feel better about gradually trying different foods and supplements to see if they make a difference.

As far as the hair mineral analysis, I honestly don’t know what to tell you about that. The scientist in me reads the literature and is skeptical, yet I know some very knowledgeable and experienced horsemen that provide this service or that use it with positive results. So I’m going to let you do some more reading and come to your own conclusions on that one!