On Matters... Equine

By Dr. Jim and Lynda McCall

We just got back from a trip to another horse farm in search of an elusive stallion prospect. After corresponding for several weeks, we finally decided these folks had a stud colt with the right breeding and color good enough to warrant venturing up into the north country.

After a long hard drive, we arrived to meet some very nice people with a pasture full of small, pot-bellied yearlings with coarse, dull hair coats. Our first thought was that the growth of these foals looked like it had been inhibited by a poor de-worming program coupled with an insufficient supply of feed. This turned out NOT to be the case. The owner of the horses was doing everything he had learned from a long family tradition of raising horses; an ample ration of oats supplemented with free-choice hay.

Still, it was obvious that these young horses had not received all the nutrients they needed. Research has shown that a well-fed stock horse will reach 90 percent of his height by one year of age: these yearlings were too small and underdeveloped, so we suspected the culprit was poor protein quality.

Protein has the unique distinction of being one of the most misunderstood of the critical nutrients for the young horse. You see, all proteins are not created equal.

There are 22 different kinds of organic compounds known collectively as amino acids, which go together in a specific way to build proteins. This phenomenon has been compared to a chain created by links of amino acids. To explain further, let's imagine building a protein out of five specific amino acids which we shall call "H", "O", "R", "S", and "E". It might happen something like this: "H" bumps into "O"; a unique molecular design allows only these two compounds to join together. Meantime "S" has found "E"; bonding has also occurred. To complete the chain, "R" must align correctly between "O" and "S" so that the specialized connecting sites can join with the appropriate partner.

As long as each link in the chain is present, protein synthesis can occur; but if just one piece is missing, the chain can not be completed — the other segments are worthless.

Fortunately, this will never be a problem for a cow, which is capable of manufacturing each and every one of the 22 amino acids. As you would expect, the horse is not so lucky. There are nine amino acids that must be provided in the diet of the horse, or he will die. The essential amino acids for a horse are histidine, isoleucine, leucine, methionine, phenylalanine, threonine, tryptophan, valine, and lysine. (Arginine is recognized as a semi-essential amino acid; the horse won't die if it is left out of his diet, but it is essential for growth and, therefore, critical for the young horse.)

All ten of these amino acids need to be supplied for the growth and development of the young horse. And "growth and development" doesn't mean just muscular development. Bone is 20 percent protein.

We hope that you are now impressed with the importance of these 10 essential amino acids for your young horse, for it's time for a pop quiz.

1. What does it mean when you read that a young horse between weaning and 12 months of age needs to be fed a diet composed of 16 percent protein?

It means that his total daily ration (both hay and grain) needs to contain 16 percent protein. If half of the ration is supplied by a 10 percent protein hay, then the grain portion of the ration must be 20 percent protein to average out to 16 percent.

What is implied is that this protein must be composed of adequate amounts of all 10 necessary amino acids.

2. Does the protein labeling information on a feed sack guarantee that the amino acid balance is correct?

Absolutely not! The label on a sack of 16 percent protein feed only guarantees that feed contains 16 percent protein; it says nothing about the QUALITY of the protein or whether it has the right amino acid balance for the horse.

So now you know the rest of the story: why it is possible to spend a lot of money and still have young horses that are protein starved. The building of the protein chains necessary for growth and development is limited by an insufficient supply of essential amino acids and the chains cannot be completed. When protein cannot be built, the body goes without, and growth and development is retarded.

This protein building is so specific that even if the diet contains adequate amounts of nine amino acids but only 50 percent of the tenth, then protein synthesis will be suppressed by 50 percent. Actually, this example is close to the truth. Most good cereal grain feeds fed to horses contain near adequate amounts of nine of the amino acids but the tenth, lysine, is usually found in insufficient quantity; lysine is commonly referred to as the limiting amino acid for horses - its lack limits growth.

So how can you find out if your feed is a QUALITY protein feed? You need to do some investigating - but first you need to be aware of a simple scientific calculation used by nutritionists called a chemical score. This test compares the amount of an amino acid (in this case, the limiting amino acid, lysine) contained in the feed with the amount required by the animal. The score is obtained by dividing the animal's requirement into the percent of the amino acid in the feed.

For example, oats run about 12 percent protein and contain .4 percent lysine. The lysine requirement for the young growing horse is .7 percent. The chemical score of oats (.4/.7) is .57; if oats comprised the entire diet of a horse it could only provide 57 percent of the necessary lysine. Since oats usually only make up half the ration, it is necessary to feed hays or supplements that will bring the chemical score of lysine in the entire ration as well as the total protein of the diet up to 16 percent. (One way that some horsemen try to get around this problem with oats is to feed twice as much oats as the young horse needs. This approach is not cost effective and, in many cases, hard to implement because young horses won't eat that much volume.)

The chemical score of lysine or the amount of lysine is the kind of information that you need to know about the grain you are feeding to your young horses. Ask your feed dealer to call the feed mill nutritionist to provide you with this data. Ask them to work with you to develop a total feeding program which will supply your growing horses with all the amino acids they need.

Don't take "We don't know exactly, but we're sure it's more than adequate!" for an answer. Investigate the resources of other feed companies in your area. Contact Extension horse specialists or animal science faculty members at a nearby college for help. But if all else fails, one shotgun approach to the problem is to buy a sack of milk replacer and add a half cup twice a day to your weanling's 16 percent grain ration and a half cup twice a day to your yearling's 14 percent grain ration. We'll bet that in six weeks you'll see a big difference!

(Visit the McCall's at their website: www.mccallhorseworld.com, or email your comments and questions to them at jimandlynda@mccallhorseworld.com)