ANN 111: Principles of Animal Nutrition and Feed Technology (2+1)

ATWATER PHYSIOLOGICAL FUEL VALUES

• While carbohydrates and fats are completely oxidized to CO₂ and water in body cells after digestion and absorption, proteins are not completely oxidized by the cell. Nitrogenous components removed from the protein in the form of urea, creatine, and uric acid that are excreted in the urine. Many combustion of urine experiments showed that the unoxidised matter is equivalent to 7.9 Kcal/gram of nitrogen, which in terms of protein is 1.25 Kcal/gram of protein.
• This energy represents metabolic loss and must be subtracted from the ‘digestible protein’. After considering this Atwater has given factors for ME, which is also known as physiological fuel values.

Atwater physiological fuel value factors

• Carbohydrate – 4.15 x 0.98 = 4 Kcal/g
• Fat – 9.40 x 0.95 = 9 Kcal/g
• Protein – (5.65 – 1.25) x 0.92 = 4 Kcal/g
• In ruminants gaseous loss also costs much of energy thus these physiological fuel values are not applicable in the case of ruminants. These values have been used in calculating the TDN of feedstuffs, but it is a crude procedure for ruminants.