Green grass is a good source of vitamin A which is present in the form of Carotene. One kg of green grass provides 50mg of vitamin A and 15 to 20g protein to the animal. Cowpea, beans, subabul leaves etc. give 30 to 40g of protein. From grass fodder herbivorous animals get the carbohydrates (energy source), proteins (“building material” of the body) and vitamins (especially carotene), which are the main drives of sustainable operation of the body. The seasonal nature of availability of green fodder and a number of byproducts necessitates preservation to feed the animals throughout the year. It is therefore essential to conserve the seasonal surplus for feeding round the year. 

Two methods are available for preserving or conserving the seasonal excess of green fodder, viz. hay making and silage making. Each method has its own limitations and advantageous. Ensiling is preferred on the basis of fodder quality.