Farmers keep livestock for obtaining milk, meat, wool, work etc. Food is the source for production for all such products as well for producing offspring. Also, a nutritionally balanced ration is a must for keeping the animals healthy and strong. Note that we call as ‘food’ of what ourselves eat. The same is known as ‘ration’ in the case of animals.
Without proper food, i.e. ration, animals cannot grow well, cannot keep good health, nor can they produce products and young ones properly. That is why we have to feed animals with nutritionally balanced and adequate quantity of rations. Hence the need to feed livestock scientifically according to their body needs.
The nutritive value of a feed is determined by analysing the quantity of various nutrients present in it, which will be available to the animal for maintenance, growth and/or production. This has to be determined with respect to energy, protein, minerals and vitamins. The simplest and earliest method of determining the nutritive value of feeds was to estimate the composition of the feed with respect to various nutrients.
It was soon found that large amounts of nutrients are lost through faeces and that the nutritive value of a feedstuff is more accurately judged when the digestible nutrients are taken into account. As a consequence, the feeding trial and digestibility trial techniques were developed.
Innumerable digestibility trials were conducted the world over to determine the digestible nutrients in various livestock feeds for all different species and classes of livestock under different conditions and activities.