Here's why:
* Urea is a source of nitrogen, not a direct source of energy. Cows need energy (calories) to grow. Urea provides nitrogen, which is essential for building proteins, but it doesn't provide the calories needed for growth.
* Urea is converted to ammonia in the rumen. Microbes in the rumen convert urea into ammonia, which is then used to synthesize microbial protein. This microbial protein provides the animal with essential amino acids.
* Urea supplementation can be beneficial for growth, but it depends on other factors. If a diet is deficient in protein, urea supplementation can improve the efficiency of protein utilization and potentially lead to increased growth. However, this effect depends on the availability of energy in the diet.
Important considerations:
* Excessive urea feeding can be toxic to cattle. Urea should only be used as a supplement under the guidance of a qualified nutritionist.
* Urea is not a substitute for high-quality protein sources. It should be used in conjunction with a balanced diet that includes adequate amounts of protein from other sources.
In summary:
While urea can contribute to growth by providing nitrogen for protein synthesis, it does not directly increase growth rate. Growth is ultimately driven by energy intake, and urea is not a source of energy.