The world is currently experiencing rapid rates of urbanisation, industrialisation and agricultural development. These activities are contributing significantly to the pollution of the environment in the form of accidental chemical discharges, exhaust fumes, wastes, sewage, by-products of manufacturing processes and other human activities. Intensive animal production is believed to be a major contributor to the pollution of the environment. For example, in pigs, about 65% of the ingested dietary nitrogen is excreted via urine and faeces,1 and this general low efficiency of N utilisation makes intensive animal production a main contributor to N pollution of the environment within the agricultural system.2
Within the European Economic Community (EEC), for example, farm animal effluents have been identified as a major source of nitrate pollution of water systems. These environmental concerns about ground water contamination with excess nitrate, phosphorus as well as other elements resulted in the issuance of Council Directive 91/670 EEC in 1991 in an attempt to limit the amount of N in slurry that can be spread on farm land.3 One of the current approaches to reducing the risk of N pollution of the environment is the reduction of N excretion in poultry by dietary manipulations involving the feeding of low-protein amino acid-supplemented diets. The overall principle is to ensure a more efficient N utilisation by supplementing low-protein diets with essential amino acids (EAAs) in better agreement with standard dietary recommendations. However, there are conflicting reports on the effects of feeding low-protein amino acid-supplemented diets to broiler chickens. While some studies4–8 have reported impaired weight gain and feed efficiency when broilers are fed low-protein diets, others9, 10 have reported identical performance with conventional formulations. The most consistent observation in these studies has been the increased deposition of abdominal fat in low-protein-fed chickens.
In all these investigations, there appear to be three points with conflicting interests: (i) the need to maintain optimal/economic poultry productivity; (ii) the need to maintain desirable (from the consumer standpoint) carcass characteristics and composition; and (iii) the compelling need to protect the environment via decreased N excretion. We believe that for low-protein amino acid-supplemented diets to command wider commercial acceptability, current research should attempt to harmonise these interests. In this paper we present the results of two concurrent trials in which broiler chickens were fed varying protein levels supplemented with EAAs to meet standard dietary recommendations. The lower-protein diets were thereafter made isoproteinous with the control by the supplementation of a composite mixture of non-essential amino acids (NEAAs). In both cases, performance, carcass characteristics, whole-body composition and efficiencies of nutrient utilisation (N excretion rates inclusive) were used as response criteria.