Applied Animal Nutrition-I

The purified diet method

PURIFIED DIET METHOD

• Purified diets were used in conducting feeding trials with lab animals. Purified diets consist of purified sources of the various nutrients.
• Carbohydrates are supplied as starch, glucose or sucrose;
• Protein is supplied as Casein, Purified soyabean protein or urea;
• Fat as lard or some oil;
• Minerals as chemically pure salts.
• Vitamins as pure crystalline compounds.

• Such a diet makes it possible to include or withdraw a given nutrient with a minimum disturbance to other nutrients.
• The influence of different levels or sources of nitrogen can be studied by including varying amounts of pure protein or amino acids without any change in the rest of the ration, whereas the addition of a natural protein source such as meat or beans would introduce many variables, because they contain many other nutrients as well.
• When more and more purified diets were fed to animals, the results obtained were discouraging, which indicated that many unidentified factors were essential. This led to the discovery of vitamins.
• In 1816, Magendie fed diets of pure sugar and of pure fat to dogs to ascertain whether or not N was required in the food.
• J.B.Boussinggault, the famous French chemist carried on nutritional studies with various species, involving the use of diets consisting in part of purified nutrients.  McCollum and Davis, Osborne and Mendel used this method.

Advantages

• This method was responsible for much of our modern knowledge of nutrition, especially poultry nutrition including the physiology of vitamins, the establishment of differences in protein quality and more exact information regarding many of the minerals.
• This method is the only method by which the role of an element needed by the body in small amounts can be effectively carried out only with basal diets where the element can be freed or added in known amounts easily.

Disadvantages

• The ingredients of these diets cannot be considered pure in the absolute sense. For example, starch cannot be entirely freed from mineral elements. Some of the vitamins were identified as “impurities”.
• Some of the constituents, notably protein, in purified diets may be altered from their natural state in the process of purification.
• The kind of pure carbohydrate used affects the significance of the results in the case of certain vitamins because of the effects of various carbohydrates on vitamin synthesis in the alimentary tract.
• All the nutrient requirements of the species should be known to prepare a completely purified diet.
• The diet must be of suitable physical nature and sufficiently palatable so that it will be consumed as per the need.