I`ve gotten several posts the past week about supplementing protein, so I think it might be worthwhile to explain a little further about when, where and why to supplement. Some of this is scientific fact, some is opinion, both mine and that of some well-respected horsepeople both in the academic community and out in the field.
The thing about feeding protein is that you don`t just want to provide quantity, you must provide QUALITY for maximum performance. When nutritionists talk about "protein quality", this is what they mean. Different sources of protein provide different amounts of the amino acids that make up protein---one source may provide a high level of one amino acid and almost zero of another, while a different protein source may provide moderate amounts of two different amino acids, etc. Every protein source is different. A "high quality" protein source is one that supplies a good variety of several essential amino acids. If you`re feeding a horse only a limited ration, for example grass hay and oats, then it is likely that the diet is deficient in one or more of the essential aa`s. The deficiency is increased if the feed quality is poor, old or moldy---anything that destroys protein. (Though if you`re feeding moldy hay, you`ve got bigger problems that protein deficiency).
When talking about amino acids, you`ll hear about the "essential" amino acids---these are the one which cannot be synthesized by the body in sufficient quantities, they MUST be provided as well in the diet. The amino acid considered the first "limiting" in horses (and other species) is lysine. It is the aa most likely to be deficient, and so if a horse`s ration contains sufficient lysine, it is almost certainly going to be sufficient in the other essential amino acids, as well.
So why do sufficient aa`s make a difference? Think of each amino acid as a different letter of the alphabet, and proteins as words. In order to make a protein (a word), you have to string together amino acids (letters) in a certain order---if you don`t have the right letter available at the right time, then you can`t substitute another letter and still get the same resulting word/protein.
So if a horse`s body is trying to respond to an increased workload, one of the many things he has to do is synthesize new muscle tissue, more metabolic enzymes, more blood cells, more regulatory hormones, etc. etc. All of them proteins. If there is an insufficient supply of a particular amino acid, then the protein in demand simply won`t be synthesized and the horse will not perform up to his maximal potential.
Here`s where we get to the opinion part. Alot of people both in the scientific community and out in the field are of the opinion that the NRC recommendations for protein for a working horse are on the conservative side. Not by a whole lot, but a few percent---in other words, lots of people feel that intensely exercising horses do better with a protein content closer to 12-14% rather than the 10% recommended by the NRC. I happen to agree that a LITTLE extra protein supplementation can make a difference, as long as the amino acids supplied are the right ones. Here`s the problem---first of all, there`s damned little information on what feeds provide exactly what amino acids in what percentage. There`s information on some of the protein supplements, but it would be helpful to know what was deficient and was wasn`t in the diet to begin with. All the data simply is not available, so it`s hard to identify whether a particular ration is really deficient or not. Deficiencies have to be identified qualitatively rather than quantitatively and that`s often hard to do.
The second problem is that equine research hasn`t come even close to catching up with the amino acid research going on in human exercise physiology. There is increasing evidence to support theories that careful supplementation of some specific amino acids might be very beneficial to performance, but so far, science is pretty clueless as to the details. As an example, alot of people feel DMG is beneficial, which is simply supplementation of a form of the amino acid glycine---but so far, there`s no proof positive, just alot of conflicting data (some of it mine). There`s also alot of speculation about some of the branched-chain amino acids, but again, nothing concrete beyond some promising data from the field. Maybe Tom can comment on this, I know he has some experience with aa`s on the track in this area.
Eventually, there might be some solid information as to exactly what amino acids are required in what quantities for maximum performance, but for right now, the best science can do is to recommend that a good variety of protein sources be made available so that (hopefully) enough of the right amino acids will be available when called for in response to increased exercise demand.
So here`s the deal with supplementing protein for endurance horses. This, of course, applies to mature horses, not growing, pregnant, lactaing or otherwise reproducing horses, all of which are a whole `nother ballgame. Horses that are being fed more than a few pounds of alfalfa, in addition to whatever other grass hays and grains in all liklihood do not need protein supplementation---alfalfa has it`s downside, but it is a good source of alot of the amino acids. If you live in an area that grows alfalfa without the high Mg levels we have here in the SW, thank your lucky stars. That doesn`t mean feed a ton of it, just a five to ten pounds along with a good grass hay is plenty. If you`re in the SSW and enteroliths are a concern, then you can minimize the alfalfa and supplement the protein (which is what I do with my own horses).
If you`re feeding your horse alot of good quality bermuda or other grass hay, then according to NRC data, he`s probably getting more or less sufficient lysine at maintenance and only short a few grams at moderate levels of work. Nobody`s going to drop dead if you choose not to supplement, but it also just might boost performance a bit if you did supplement just a little. This is where you should keep everything else in the diet as is, try adding just a bit of good-quality protein and see what happens. Improvements to look for would be an increase in lean muscle mass, improved hair coat and hoof quality as well as improvements in performance itself---in endurance horses, look for slightly better recoveries, maybe lower heart rates, longer time to fatigue. Most endurance people know their horses well enough to know bright-eyed and bushy-tailed when they see it.
More is not better, by the way. Boosting protein levels up too much has deletorious effects as well.
So far, the best sources of high-quality protein are still the oilseed meals, such as soybean, linseed and cottonseed meal, and milk replacer pellets, such as Foal-Lac. Of the oilseed meals, soybean has the best amino acid balance, and is very digestible (the amino acids are readily available for absorption, not otherwise bound up as they are in some of the grains, such as corn). Because soybean meal is VERY high in protein, usually around 44%, it doesn`t take much to supplement even an intensely working horse. One pound will provide over 13 grams of lysine, which should be plenty, without getting into excessive amounts of nitrogen. Don`t EVER feed whole raw soybeans, though, as the whole seed contains a substance that inhibits the enzymatic digestion of protein. The heat of milling soybeans into meal destroys this inhibitor.
As usual, somebody asked me a simple question of what time it was and I responded with a 300-page manual of how to build a watch. :-D Hope this answered everyone`s questions about lysine and protein supplementation.
Susan Evans Garlinghouse
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The use of protein percentage as a comparison guideline can be misleading. I prefer to use protein level normalized to DE. For example, say you are feeding a diet of only midbloom timothy with a protein level of 8.6%. You want to increase protein and barley with a protein level of 11.7%. Assuming the horse maintains weight on both diets, with the substitution of barley the horse will eat LESS protein.
The problem: Barley despite the high percentage (11.7%) is an energy dense feed causing the horse to consume substantially less food (by weight) than when he was on the timothy only diet.
Normalized to DE, the protein content of barley is only 35.9 g/Mcal and for mid bloom timothy it is 48.6 g/Mcal. In other words for every Mcal of food consumption, the timothy will supply 48.6 g of protein while the barley will supply only 35.9 g.
Of course the other issues are still there - digestibility (on which there is very little data) and amino acid balance - but the same principle would apply if one could obtain figures on say digestible lysine content of orchardgrass. A number normaized to DE rather than raw percentage would be a better means of comparison.
Duncan Fletcher
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I did a survey of the rations fed to horses both at the Old Dominion ande the 1985 Race of Champions and correlated the results with the incidence of pulls for metabolic reasons. Yes, that info is ten years old but I did a similar study only three years ago at the Essex three day event horse trials and came up with almost identical results. Even though the 3-day horses do a lot more anaerobic work, they still must have incredible endurance to do what they do and the metabolic demands placed on them are much more similar to our endurance horses than Tom`s rachorses (sorry, Tom-you are definitely the expert on racehorses that complete their task in under two minutes, but sometimes your track race horse wisdom racehorse wisdomcan be downright dangerous for horses working much longer, slower distances).
Bottom line: the top ten performers in both groups were fed an average of 11-12% protein in their total ration and an average of 5 lbs of grain. In the endurance study the horses that failed to complete (n= only 4) had a tendency (p<.06) to be fed more grain and less hay than the ones which completed (n=50). Only 13 of the endurance horses were fed only alfalfa, and if memory serves me right, most of those were from (surprise) California. The number of puls was so low, however, that statistically it was hard to draw conclusions regarding protein, but the conclusion was made that feeding more than average protein did not confer any benefit. Reference for those interested in the details Ralston, SL: Nutritional Management of Horses competing in 160 KM races Cornell Vet 78:53-61, 1888.
In the three day horses (92 horss total, 18 of which were pulled for metabolic reasons, so a much better # to compare), 48% of the competitors fed no alfaalfa, jualfa just plain old grass hay. Only 8.8% of the horses were on alfalfa only. They did tend to be fed more grain than the endurance horses (9.5 lbs/day) or 35% of the tota ration but again there was a correlation with high grain/low forage intake and metabolic failure. When I compared horses fed >16% protein rations to those on !4% or lower, the high protein horses that actually completed the endurance phase had higher respiration rates and slower heart rate recoveries than the low protein fed horses. They also had a significantly higher rate of metabolic failure. A very brief abstract of this work was published inAndrew Clarke and Leo Jeffcott`s book: On to Atlanta `96, published in 1995 by the Equine research Centre at Guelph. I highly reco0mmend it to those looking for recent, practical research on high level Performance horses - a lot of good research is presented in the book.
Sarah Ralston, VMD, PhD
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