Body Wisdom: Absorption Of Vitamins

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Your horse, like every living thing, relies on vitamins for a variety of body functions and would die without them. So, yes, your horse needs vitamins. However, that doesn’t necessarily mean you need to supplement them above and beyond what’s in his current diet.

Whether or not your horse needs a supplement depends on two things — the level already present in his diet and what his needs are. If needs are being met by diet, he doesn’t need more. It’s that simple. More is not better. At best, more is a waste but harmless; at worst, more is toxic.

Common sense alone tells us that the horse evolved as a species by being able to survive on the nutrients available to him. The horse’s ancestors moved from browsers to grazers (grass eaters) around 18 million years ago. Grass is a horse’s natural food, and a healthy horse with an adequate supply of fresh/live grass pretty much doesn’t need additional vitamins. Even in winter, a horse’s diet isn’t as devoid of “live” material as you might think. Dormant (not actually dead) grasses still contain active vitamins, and the diet is supplemented by browsing on the tightly closed buds and more tender distal ends of shrubs and trees. Even so, vitamins are not as available as during periods of active growth of grasses.

Vitamins with the highest potential for toxicity are the fat-soluble vitamins: A, D and K. The horse is protected from A toxicity under natural circumstances by his ability to limit how much of the abundant beta-carotene — the vitamin A precursor in plants — is actually converted to vitamin A. There are no “active” forms of vitamin D in the diet, so natural safety from that poisoning is also through regulation of how much inactive vitamin D from plants (also produced in the skin) gets converted to active D. An identical situation exists for vitamin K, where K3 is the active form but the horse absorbs either K1 (plants) or K2 (from intestinal bacteria), which the body must then “activate” to K3.

Vitamin E has little, if any, toxicity and the horse will absorb E in direct proportion to how much is present in the diet. Vitamin C and the B vitamins are also relatively nontoxic and will be absorbed in proportion to what is present in the diet. Horses on good pasture have much higher levels of these vitamins in their blood than stabled, unsupplemented horses. However, full-blown deficiencies of C or the Bs do not occur in horses. With vitamin C, the horse is protected because he’s able to synthesize at least enough to prevent full-blown scurvy. All foods contain some (albeit low levels) B vitamins and synthesis of Bs by bacteria in the lower portions of the small intestine is another source. In addition, research in other species has found that absorption of Bs can be increased by activation of special carrier proteins on the intestinal lining cells.

A healthy horse on good pasture doesn’t need supplemental vitamins, except for E in some instances. Vitamins B12, D and K probably never need to be supplemented. Vitamin A should be given as a supplement with caution, if at all. That leaves just vitamin C and the B vitamins.

While it’s likely working horses would benefit from some supplementation of C and B vitamins when they are on hay-and-grain diets, precisely how much is largely a matter of guess work. Our chart lists some guidelines for amounts to supplement for horses in moderate or heavy (racing, endurance, upper-level eventing) work, and how the multi vitamin and mineral supplements from our previous mineral articles compare.

Requirements for vitamin C and the B vitamins may be increased in a variety of situations, including:

• Injury or surgery
• Antibiotic use
• Heavy exercise
• Allergies
• Bowel problems, especially involving the small intestine
• Liver disease
• Old age.

Bottom Line
Unless you’re buying single-ingredient products, it’s difficult, if not impossible, to find a supplement that contain only vitamins or only minerals. In most cases, levels of the fat-soluble vitamins (A, D and K) are higher than they really need to be, while E is too low. C and B vitamin levels are all over the place, although it’s difficult to criticize that when our understanding of dietary requirements for horses is so poor.

If we look at our favorite products for mineral supplementation for performance horses on hay and oats, we’ll see that Triple Crown12, the clear winner on the mineral end in our last mineral article, also does a good job with the most critical vitamin, vitamin E. Vitamins A and D levels are higher than they need to be for performance horses, but they’re still safe and, since the supplement also targets growing horse and pregnant/lactating mares, there’s no getting around the higher levels there. The product contains no vitamin K, which is good. On the C and B vitamin fronts, although the ingredients list has all the Bs on it, only the level of biotin is guaranteed, which is good at 2.8 mg, just above the estimated minimum requirement of 2 mg per day. We’d also like to see a guaranteed level for at least thiamine.

TDI 10 took a similar conservative approach by guaranteeing only low to modest levels of biotin, riboflavin and thiamine (other Bs in there, but levels not guaranteed), but it has fairly good levels of E (1000 IU for performance dose). They went easy on the A and D, no K, which we like. Sport Horse and Performance Plus were the heavy hitters for B vitamins, also providing good levels of vitamin E, sane levels of A and D. If your performance horse has trouble handling stress, nervousness, vague or not so vague muscular complaints, gut disturbances, one of these two may be ideal for you. Pennwoods Equine Supreme has too much A and D for us, low E and low levels of Bs. Same on the A, D and E for Equi-Shine, with middle of the road inclusion of B vitamins. Nutri-Plus++ also has a nice profile of B vitamins and vitamin E, more A than you need with good hays, but safe.

Picking a winner on the vitamin end of things is even more difficult than with minerals, for the simple reason that each horse is different. This is compounded by the fact that solid information regarding equine vitamin requirements is simply not available. The situation is also complicated by the fact that the potentially most critical vitamins — vitamin E and the Bs — are also fragile in a combination vitamin/mineral mix.

For a supplement that covers the known basics well, we’d again have to go with Triple Crown 12 with its generous E levels, above minimum biotin and because the mineral profile in this multi is the most versatile. However, some horses will benefit from higher levels of B supplementation. If you have a horse that fits the profile of one likely to benefit from Bs, and if these supplements are compatible with your hay mineral profile, try Sport Horse or Performance Plus.

Contact Your Local Tack/Feed Store Or:

• ACCEL, $19/5 lbs., 800-848-2359
• DYNAMITE PLUS, $25.50/5 lbs.,, 800-69 7-7434
• VITA-PLUS, $13/3 lbs., 800-234-2269
• MAXUM, $9.50/2.5 lbs., 800-234-2269
• PENNWOODS EQUINE SUPREME BLUE, $16/8 lbs., 800-255-3066
• GRAND VITE, $24/5 lbs., 800-255-2962
• MEGA CELL, $17.50/5 lbs., 800-328-6652
• EQUI-SHINE, $10/6 lbs., 800-639-0249
• AUGMENT ULTRA, $41.95/10 lbs., 866-233-7887
• SELECT II, $19.95/5.66 lbs., 800-648-0950
• DIRECT ACTION (DAC), $20/5 lbs., 800-921-9121
• EQUI-BASE, $15.50/10 lbs., 800-248-0330
• TRIPLE CROWN 12% SUPPLEMENT, $40/50 lbs., 800-451-9916
• LINPRO, $27.50/5 lbs., 540-942-4500
• PLATINUM PERFORMANCE EQUINE, $50/10 lbs., 800-553-2400
• TDI-10, na/$50 lbs., 800-457-7577
• FORMULA 707, $27.95/ 12 lbs., 800-525-8601
• HS-35, $35/50 lbs., 888-875-2425
• PERFORMANCE PLUS, $27/5 lbs., 800-356-8776

This is part of a series on nutrition. Our July 2005 article looked at the mineral needs of horses at maintenance or low-level work. In October 2005, we tackled the mineral needs of performance horses. See, 800-424-4887.

Also With This Article
”Vitamin E Requirements Listed As IU/Day”
”Vitamin Supplements Comparison Of Products”
”B Vitamins And The Gut”