If supplementation is to be both economical and successful, it needs to be based on scientific principles and thus the physiology of the ruminant must be clearly understood. The rumen dominates the digestive system of the animal, in which there exists a large number of microorganisms. The microorganisms are able to ferment feed components including carbohydrates and protein to simple organic acids known as Volatile Fatty Acids (VFA). The energy released in this fermentation process is used by the microorganisms to build their own cells and the VFA’s are the nutrients that provide most of the energy for the animals. The dead rumen microbes then supply the majority of the protein requirements for the animal. Usually, most of the protein eaten by the animal is highly soluble (like urea), and will be fermented in the rumen to produce VFA’s and ammonia. If any dietary protein proves to be insoluble in the rumen, it will pass out of the rumen and down he digestive tract relatively unchanged until it enter the small intestine. This is called by-pass protein and when digested in the small intestine, becomes available to the animal as amino acids. Thus, the protein requirements of the ruminant are derived from two sources:

• The digested remains of rumen microorganisms.
• Dietary by-pass protein.

When designing supplements for ruminants, the primary objective is feeding the microorganisms in the rumen. The growth of rumen microorganisms requires the presence of a nitrogen source, ammonia, which usually arises from digested dietary proteins, such as found in pastures, urea, grains, etc. Sheep and cattle pass urea back to the rumen by means of saliva. The amount that enters the rumen depends on the protein content of the diet. If the ammonia levels in the rumen are low, this indicates that the protein intake is deficient. Rumen microorganisms require other trace elements and minerals, such as sulphur and phosphorus.

The other important principle to be taken into account when formulating a supplement, it the protein requirements of the animal itself. The ruminant, as distinct from the rumen microorganisms, has a variable demand for protein during its growth and production, to be used for tissue synthesis , wool production, milk production, etc. The animal requires quite large amounts of protein during the early stages of growth, late pregnancy and lactation. The supply of protein for digestion derived largely from microbial growth in the rumen, is generally insufficient to meet the requirements for these critical stages. The extra protein required during these periods must be supplied in the diet as bypass proteins. Feed supplements must contain a significant proportion of by-pass protein during weaning, pregnancy and lactation of all ruminants.