Here is a list of several articles on the subject. These are all veterinary research, and worth the read. There are many more studies than these, so it may be a mistake to base your opinion on any one study. Note the dates of the research, as it spans some time. Also note that there are several pages to search.http://www.thehorse.com/Search.aspx?cx=001813077443207757262%3A-qbps-ljkta&cof=FORID%3A9&ie=UTF-8&q=grass+hay+for+ulcers&sa.x=37&sa.y=7#0Here is an exerpt from an article by a noted equine nutritionist, Karen Briggs, regarding the building blocks of protein, called amino acids..................."Of all the components of your horse's diet, protein is probably the most misunderstood. Protein's real role is not to act as an energy source for performance, but to provide amino acids, the building blocks for growth and repair of bones, muscles, and soft tissues. Amino acids are involved in virtually all of the horse's vital processes. They are essential to the synthesis and the release of hormones, the synthesis of neurotransmitters and enzymes, and the regulation of sleep, appetite, and blood pressure, to name just a few functions. But primarily, amino acids are needed for the formation and repair of muscle tissue, bone, and other soft tissues throughout the body. Growing horses which are "building" new tissues as they mature, and horses being used for breeding, have a higher protein requirement than do mature horses being used for pleasure or performance. Whether working or idle, the protein needs of most mature horses are surprisingly small (between 8% and 11% crude protein in the overall diet, as opposed to 12% to 16% for a young, growing horse or lactating broodmare). Proteins are "chains" made up of various combinations of the 22 amino acids that exist in nature. The position and number of the amino acids in a single protein make up its "amino acid profile." When a horse ingests protein, the chain of amino acids is broken up in the digestive tract by enzymes and acids, and the individual amino acids are absorbed through the wall of the small intestine and into the bloodstream via the liver. From there, they travel to the sites where they are most needed. Although amino acids are absorbed from the small intestine in a format relatively unchanged from their original chemical composition, the horse's body does have the ability to change some amino acids into different formats as the need exists, a process that occurs in the liver. You must remember, however, that the horse's body does not have the ability to create all the amino acids it needs. Some amino acids only can be synthesized by microorganisms or green plants; these are called the "essential" amino acids, and they must be obtained by the horse from his environment. ("Non-essential" amino acids are those the horse can synthesize himself.) A good-quality protein source is a food that provides a sufficient amount of essential amino acids, particularly the amino acids lysine and methionine. Lysine is often called the "first limiting" amino acid, meaning that if insufficient quantities of lysine are present, then the horse's body will have difficulty utilizing any of the other amino acids. Methionine is second in line. The best source of high-lysine protein for foals is milk protein; for adult horses, a plant source such as soybean meal is the best way to go. (Cottonseed meal and linseed meal, two other common protein sources used in horse feeds, have far less lysine and thus aren't considered to be as high in quality as soybean meal.) That said, the amino acid profile of a feed is more important to a young, growing horse than to a mature one; adult horses are far less sensitive to differences in protein quality. Lysine and methionine often are deficient in the ingredients that make up normal horse feeds, but since they can be synthesized inexpensively, it's routine for feed companies to add these to improve the overall amino acid profile. (Not all amino acids can be easily synthesized, however.) Can protein serve as an energy source? Yes, but metabolically, it's an expensive process, producing three to six times more body heat than the breakdown of carbohydrates or fats, and yielding considerably less energy. The heating factor might be beneficial in a cold environment, but it can contribute to excessive sweating and possible heat exhaustion during hard work, especially in a warmer climate. Since protein is one of the more expensive ingredients in a feed, it's impractical to feed higher levels of protein in search of a performance advantage. Carbohydrates and fats are better energy sources (more on them in a minute). Feeding more protein than is needed is false economy for other reasons, too. Any protein that is not used immediately by the horse's system is converted to ammonia and urea molecules, which are excreted in the urine. This leads to increased water intake, increased urination, and a noticeably strong ammonia smell in the stall."
