Urea, also known as carbamide, is an organic compound with the chemical formula CO(NH2)2. This amide has two –NH2 groups joined by a carbonyl (C=O) functional group.

Urea serves an important role in the metabolism of nitrogen-containing compounds by animals and is the main nitrogen-containing substance in the urine of mammals. It is a colorless, odorless solid, highly soluble in water, and practically non-toxic (LD50 is 15 g/kg for rats). Dissolved in water, it is neither acidic nor alkaline. The body uses it in many processes, most notably nitrogen excretion. The liver forms it by combining two ammonia molecules (NH3) with a carbo dioxide (CO2) molecule in the urea cycle. Urea is widely used in fertilizers as a source of nitrogen and is an important raw material for the chemical industry.

The need to supplement.
As grasses mature and seed their feed value declines. The nutrients in the grass also become less accessible to cattle as grasses become harder to digest as they mature. As a result of this decline in pasture quality and digestibility cattle lose weight at an increasing rate as the dry season progresses.

In a grazing sense little can be done to improve the digestibility of mature grass but supplements can increase the rate at which digestion does occur. Faster digestion results in an increase in the amount of grass eaten. An analogy is the marketing strategy of low margin high turnover. In this case low digestibility higher intake results in improved animal performance.

Nitrogen to Sulfur ratio.
For cattle the optimum ratio of nitrogen to sulfurin in the diet is about 13:1. This is about the same ratio as found in leaf protein, and as the pasture declines, the ratio remains constant. Hence, when supplementation with urea N commences, it would be beneficial to include a sulfur source. Without it, the utilisation of the urea and the dry feed may be reduced and a sulfur deficiency may occur.