Protein Excess
If more protein is ingested than needed, nitrogen, in the form of ammonia, is removed from the amino acids that make up the protein. The remainder of the amino acid is used for energy, or, if energy is not needed at that time, it is stored as fat or glycogen for later use as energy. The ammonia that is removed from the amino acids is converted by the liver to urea. This increases the plasma or blood urea nitrogen concentration (BUN) which is directly related to dietary protein intake. The increased amount of urea produced is excreted in the urine. This increases urine volume and water requirements. It also increases the ammonia smell in the urine which can be noticed in poorly ventilated stables when horses are fed higher-protein-containing feeds such as alfalfa.
The more protein eaten above the animal’s needs, the greater the blood flow through the kidney. Prolonged renal hyperperfusion from chronic excessive protein intake is known to decrease renal function in people and some species of animals. Currently there appear to be no studies of whether this occurs in horses. Even if it does, it is doubtful that it would be a problem in any practical situation. However, if the horse, like other animals and people, has a decrease in hepatic function, there is a decreased ability to convert ammonia to urea; or, if there is a decrease in renal function, there is a decreased ability to excrete urea, and the amount of ammonia or urea in the body increases. Limiting protein intake to that just sufficient to meet needs is, therefore, beneficial in the management of an animal with liver or kidney disease.
The utilization of protein for energy produces three to six times more heat than the utilization of carbohydrates or fats. This may be beneficial in a cold environment, but may contribute to excessive sweating and heat exhaustion during physical activity, particularly in a warm environment. Although some have claimed that high-protein diets for horses impair endurance performance, others are unable to find any beneficial or detrimental effects. Excessive protein intake may, however, contribute to developmental orthopedic diseases.
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