|
|
|
|
|
Nonprotein Nitrogen (Urea) for Horses
Microbial organisms present in the rumen of cattle, sheep, and other ruminants, and in the cecum and colon of the horse, are able to utilize the nitrogen in urea or other nonprotein nitrogen-containing substances to synthesize protein, providing the animal consumes sufficient nonfiber sources of dietary energy. In ruminants, the protein produced by these organisms passes from the rumen to the stomach and small intestine, where it is digested and absorbed. Thus, a nonprotein source of nitrogen, such as urea, may be fed to ruminants to provide them with protein. If all of the urea ingested is converted to protein, one unit of urea would provide 2.81 units of protein, since most feed-grade urea used currently contains 45% nitrogen, and protein contains 16% nitrogen (45% 0.16 281%). However, feeding urea or nonprotein nitrogen is of little value in providing protein to the horse. Most of the nonprotein nitrogen fed to the horse is absorbed from the small intestine and excreted in the urine before it reaches the cecum and colon, where it may be used for protein synthesis. Although that which reaches the cecum and colon may be used for protein synthesis, little of it is digested and absorbed from the cecum or large intestine. Thus, although some of the nonprotein nitrogen fed to the horse may be used for protein synthesis, much of that protein is unavailable to the horse and, therefore, is excreted in the feces.
By U.S. law, feeds containing nonprotein nitrogen must state on the feed tag the amount of protein from nonprotein nitrogen. It is important to realize that the feed will provide this amount of protein only if all of the nonprotein nitrogen it contains is converted to protein and is utilized by the animal. Since little of it is utilized by the horse, this amount should be subtracted from the feed’s protein content to determine how much protein that feed will provide the horse. For example: a feed tag states that the feed contains 26% crude protein with 10% protein equivalents from urea. This feed, therefore, provides only 26% 10%, or 16%, crude protein for the horse. The 10% protein equivalent from the urea is of no benefit (or harm) to the horse.
Excessive intake of nonprotein nitrogen is toxic. Before microorganisms use nonprotein nitrogen to synthesize protein, the nonprotein nitrogen is converted to ammonia. If an excessive amount of nonprotein nitrogen is ingested, toxic quantities of ammonia are absorbed. Initially, affected animals wander aimlessly and are in coordinated. Following this, they may press their heads against fixed objects, become recumbent, then comatose, convulse, and die. Although ponies succumb to single doses of 0.5 kg (1.1 lbs) of urea, intakes of feed containing up to 5% urea (14% protein equivalents from urea) as the total diet, and providing as much as 0.25 kg (0.55 lb) of urea daily, do not have any detrimental effects on mature horses. This is several times greater than the amounts that are toxic to cattle or sheep. Therefore, diets made for cattle or sheep that contain urea, or other nonprotein nitrogen sources, may be fed to the horse. Even though the nonprotein nitrogen compound is of little benefit to the horse, it is not harmful in the amounts present in these diets.
Submit Your Question
|
|
|
