When we asked some non-farmers what they always wanted to know about the farm, here’s the first thing they came up with: “What is urea and why is it poisonous to horses?”  Makes sense, I guess, since many urban people’s only experience with the farm is owning or riding a horse.

Urea is a common substance found in Nitrogen fertilizers. It also has toxins that can affect horses.  It is most widely used as a solid Nitrogen fertilizer throughout the world. Urea is also often found naturally in nature since it is a compound in animal urine. As a fertilizer it is commonly used on farms, and in application to crop fields.  In crops, especially corn, Nitrogen fertilizer is essential for crop germination and growth. Nitrogen fertilizer is commonly applied to fields after harvest, in the fall. Urea is another form of Nitrogen fertilizer that also helps the crops to grow. Failure to add Nitrogen to field soils can result in stunting of crops, which is when the crop develops at a shorter than normal length.

The most common way Urea is used in fertilizer is when it is mixed with soil, or it can be applied to the soil surface. Urea is also a highly soluble substance and can be dissolved in water and applied to the soil as a solution, and therefore may be sprayed onto the crop leaves.  When the Urea makes contact with either the soil or the plants, a naturally occurring enzyme called urease begins to quickly convert the Urea to a gas through a process called hydrolysis. This process will generally take place within several days after being applied to a field.

Urea is a non-protein nitrogen source that is commonly used in diets for ruminant animals, most commonly cows. The purpose of Urea is for use in the synthesis of microbial protein which is then used to meet a great portion of the cows’ protein requirements for their diet. The arrangement of a horse’s gastrointestinal tract makes the use of Urea questionable for their nitrogen requirement for their diets.  It has been found that small amounts of the protein intake may be beneficial, especially for mature horses that receive a large amount of a forage diet. Recently it has been found that Urea may also be toxic to horses.

Because horses are non-ruminants, opposite cows, they do not have multiple stomach compartments, as cows have 4.  This has a great impact on how we should feed our horses in comparison to cows and why they differ in their nutritional needs. The problem with Urea and horses is that commonly horses and cattle are fed together, and since cows require a supplement such as Urea, horses also consume it, and a specific amount turns toxic in the horses’ intestines, and results in death to the horse.

Urea is one feed additive that horses are less susceptible to than ruminants. Urea is usually lethal at 1-1.15 g/kg body weight, but 0.3-0.5 g/kg may be toxic; in horses, 4 g/kg body weight is lethal. Ideally, a urea level in the feed which is safe for cattle should also be safe for horses. However, the horse’s digestive system is not constructed to efficiently utilize NPN, so they are not used in horse feed.”

Jessica Kozak
University of Illinois student

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