Alfalfa hay has a high protein and calcium content but feeding it does not harm horses with normal kidneys. Because of its high protein content, when alfalfa is fed to mature horses, the stall may smell strongly of ammonia. The ammonia is the extra protein that the horse did not need and which it had to get rid of in the urine. The other characteristic of the urine of horse being fed alfalfa is a reddy-whitish color. This is the extra calcium that is being voided. Other biases against alfalfa are that it is dusty, mouldy and causes colic. These conditions can occur with any feed that is poorly cured or carbohydrate rich. However, alfalfa is a nutrient rich feed and is the hay of choice for young growing horses and lactating mares.