Effect of Diets Formulated on the Basis of Four Critical Essential Amino Acids on Performance and Blood Biochemical Indices of Broiler Finisher Chickens Reared under Tropical Environment

A study was conducted in a completely randomized design to evaluate the effect of diets formulated on the basis of four critical essential amino acids (lysine, methionine, tryptophan and threonine) on the crude protein requirement, carcass quality, nutrient digestibility, haematological and blood biochemical indices of broiler finisher chickens (28-56 days) reared under tropical environment. One hundred and eighty chickens were used in this experiment. There were four experimental diets each with three replicates (15 birds per replicate). The experimental diets were formulated with a gradual crude protein increase from 18 to 21% in 1% intervals. Diet 1, 2, 3 and 4 contained 18, 19, 20 and 21% dietary crude protein, respectively. Ileal digestible quantities of all essential amino acids (EAA) were almost equal in the diets and total amount of each EAA was maintained at or above NRC requirements. The performance of chickens fed 19% crude protein (CP) was similar to chickens fed 20 and 21% CP diets in terms of final weight, weight gain and feed conversion ratio. Feeding 18% CP with essential amino acids resulted in significantly (P<0.05) lower final weight, weight gain, average daily weight gain and poorer feed conversion ratio (FCR) than those fed diets higher crude protein diets. Generally, it was observed that chickens fed 19, 20 and 21% CP supplemented with balanced essential amino acids were statistically similar in terms of the carcass weight, dressing percentage, thighs, drumsticks, heart, lung and back weights compared to the chickens fed 18% CP supplemented with balanced essential amino acids. Chickens fed 21% CP fortified with balanced essential amino acids had the best values for apparent digestible crude protein, crude fibre (CF) and nitrogen free extract (NFE) compared with the chickens fed 18% CP with balanced essential amino acid. The observed means for most of the haematological and blood biochemical indices fell within the normal values for healthy chickens. It can be concluded that crude protein requirement of broiler finisher chickens (28-56 days) can be reduced to 19% with essential amino acids supplementation without having any adverse effect on growth, nutrient digestibility, carcass quality and haematological parameters of broiler finisher chickens reared under the tropical environment.