In July 2005, we looked at 20 widely available supplements and how they worked for three hay-based diets from across the country, with an eye toward the horse at maintenance. This time, we’ll see how these supplements measure up in performance-horse diets of hay and plain oats.
Our model horse is still an 1,100-lb. adult, but now he’s doing moderate work, which we’ll define as 45 to 60 minutes per day of uninterrupted formal activity, most at the trot and canter.
In our first article, our horse at maintenance was being fed 22 lbs. of hay a day, with maybe just enough grain or beet pulp to get his supplements in, but not enough to significantly influence the mineral balance of the diet. This time the horse is working fairly hard, so we’re also giving him 11 lbs./day of plain oats.
Please note that if your horse doesn’t require that much grain to hold his weight when in moderate work, your analysis will turn out differently. We used the same sample hays as in the first article, and the same supplements, but with dosage adjustments if manufacturers made different recommendations for working horses, and substitution of products if the first ones were not strongly recommended for horses in work.
Obviously a horse in work needs more calories and more protein, to repair hard-working muscles and build muscle bulk. However, the crude percent protein in the diet doesn’t have to increase. Some horses do benefit from provision of specific amino acids to help them build and repair muscles. Providing more than the minimum of vitamins can also be an important consideration.
On the mineral end of things, we use the current NRC recommendations on calcium and phosphorus but go somewhat higher on magnesium requirements.
Trace-mineral recommendations are those currently accepted. Since these levels are already comfortably above the last NRC recommended minimums, we didn’t increase them for the horse in moderate work.
However, the selenium recommendation of 2 mg/day is sometimes too low to maintain an optimal selenium concentration in the blood. Intakes of 3 to 5 mg/day for a 1,100-lb. horse are safe and may be required by some horses. The risk of chronic toxicity begins at about 20 mg/day.
Targets And Ratios
The target mineral levels in the charts of our three hay types are recommended minimums to feed. That means you shouldn’t settle for intakes below these levels. With the exception of iron, higher-than-minimum intakes are usually well-compensated for by either decreased absorption or increased excretion, so are safe.
High-iron intakes over time can be especially hazardous because the body doesn’t have any way to actively excrete it, so the iron accumulates in the tissues, contributing to cellular oxidative damage. While other minerals at intakes as high as 6, 8 or even 10+ times the minimum aren’t directly toxic, they do compete with other minerals for absorption, which is where the ratios come in. We’ll address these individual nutrtional ratios:
• Ca:P ratio: A calcium:phosphorus ratio lower than 1.2:1, also often referred to as an “inverted” Ca:P ratio when less than 1:1, puts the horse at risk of serious nutritional bone disease, called “nutritional secondary hyperparathyroidism.” This is definitely a situation you want to avoid.
Otherwise, Ca:P ratios of as high as 6:1 are tolerated by adults, at least over short periods of time, by adjusting the amount of calcium they absorb and slowing down release of calcium from bone stores, so if you have to settle for less than ideal, go a little high.
• Ca:Mg ratio: It will be interesting to see what the new version of the NRC requirements has to say about calcium:magnesium ratios when it’s finally out.
Magnesium is an important mineral that has been a bit of a stepchild in equine nutrition, and we agree with the nutritionists who strongly feel the current recommendations are too low for horses in work. The most common symptoms of suboptimal intake in performance horses are nervousness, sensitivity to sound and touch, and muscular symptoms ranging from twitching to increased muscle tone (“hard” muscles) to frank cramping, with weakness in extreme cases.
However, as is true of minerals across the board, individual horses seem to vary quite a bit in their sensitivity to magnesium intakes. The current recommendation of a Ca:Mg of 3:1 works just fine for some horses. The 2:1 ratio is considered ideal for several other monogastric species. Low and/or inverted Ca:Mg ratios should be avoided.
• Cu:Fe ratio: The listed copper:iron ratio of 1:4 corresponds to NRC recommended minimum intakes for those minerals. In reality, much higher ratios are often encountered. The effect long-term intakes of high iron has on copper status is unknown in horses. However, adequate intake of copper is necessary for normal handling of iron.
• Cu:Z and Cu:Mn: Excesses of any trace mineral — Cu, copper; Z, zinc; Mn, manganese — have the potential to interfere with absorption of the others. The closer you can get to ideal, the better. Since copper takes many “hits” in terms of competing minerals, and copper absorption can also be negatively affected by high sulfur in the diet, if you have to choose between copper being slightly high vs. low, it’s usually best to err a little on the high side.
There aren’t many standouts here. When plain oats were added to hay #1, the diet became heavy in phosphorus, to the point that only one of the 20 supplements, Triple Crown 12, was able to reverse the dangerously inverted Ca:P ratio. Three others brought the individual minerals all into their target ranges but couldn’t reverse the low Ca:P ratio.
Triple Crown 12, Sport Horse, Equi-Shine, TDI-10 and Pennwoods Equine Supreme were the standouts for Hay #2 and oats, with Triple Crown 12 again having a slight advantage in terms of ratios since the Ca:P ratio, while high by our strict criteria, was only very slightly elevated at 2.18:1, well within what an adult horse should be able to tolerate well.
For Hay #3 plus oats, the same five supplements as for hay #2, plus Performance Plus, brought all totals into target ranges, while the Triple Crown 12 again gets the nod for having the most ratios in the ideal range. None of the supplements could correct the high Cu:Fe ratio.
With the serious problems encountered when plain oats were added to a low-calcium hay (#1), you may wonder if the solution to avoiding that would be to just feed a commercial, supplemented grain mix instead of plain grains. We’ll address that in the next article in this series.