Growth , body-fat deposition , nitrogen excretion and efficiencies of nutrients utilization in broiler-chicks fed low-protein diets supplemented with amino acids , conjugated linoleic acid or an a-glucosidase inhibitor Wachstum , Körperfettansatz , Stickstoffausscheidung und Nährstoffverwertung von 

It is now generally recognised that intensive animal production is a major contributor to pollution of environment. Within the European Union for example, farm animal effluents have been identified as a major source of nitrate pollution of water systems. These environmental concerns regarding groundwater contamination with nitrate, phosphorus and other elements led to the issuance of a Council Directive in 1991, limiting the amount of N in slurry to be spread on farm lands. For example, in pigs or poultry about 65% of the the ingested dietary-N is excreted via urine and faeces (Kirchgessner and Roth, 1993) implying that the efficiency of utilization of dietary protein by these species is only about 35–40%. One of the current approaches to reduce the risk of N pollution of the environment is via dietary manipulations involving the feeding of low-protein amino acid-supplemented diets (Aletor et al., 2000; Gruber et al., 2000). The overall principle is to ensure a more efficient dietary-N utilization by these animals by feeding them low-protein diets supplemented with essential amino acids (EAAs) in better agreement with standard dietary recommendations. In an earlier report (Aletor et al., 2000) it was demonstrated that feeding low-protein diets confers potential economic advantage while the accompanying increased efficiency of dietary Nutilization lowers the amount of excretable N into the atmosphere. However, while N-excretion was decreased by as much as 41% without affecting weight gain, a consistent observation in low-protein feeding to broilers is the substantial increase in body fat retention (deposition). The increased carcass fatness is undesirable, not only from the point of view of nutrient economy, but also product quality and human health considerations. One suggested approach to attain desirable carcass fat levels in low-protein fed broilers, relate to the dietary incorporation of conjugated linoleic acids (CLAs). The CLAs are a mixture of positional (9,11 or 10, 12) and geometric (cis and trans) isomers of linoleic acid (cis-9, cis-12-octadecadienoic acid) with only one single bond separating their double bonds (Fritsche and Steinhart, 1998) unlike linoleic acid which has its double bond separated by two single bonds. Although CLAs occur naturally in dairy products and ruminant meat, they are currently being produced industrially by alkaline isomerization. Some of the biological activities ascribed to CLAs include anti-carcinogenesis (Ha et al., 1987), immune modulation (Cooke et al., 1993), enhanced weight gain and feed efficiency (Chin et al., 1994), prevention of atherosclerosis (Lee et al., 1994), body fat reduction and body nutrient repartitioning (Pariza et al., 1996; Park et al., 1999; Jahreis et al., 1999; Simon et al., 2000). Another dietary supplement with potential for body fat reduction is Precose (Acarbose) or Bay g 5421. Bay g 5421 contains oral a-glucosidase inhibitors currently used in the management of Type 2 diabetes mellitus in humans. It is an oligosaccharide obtained from the fermentation process of a micro-organism, Actinoplanes utahensis (Bayer, 1999) and it is chemically known as O-4,6-dideoxy{{(1S,4R,5S,6S)-4,5,6-trihydroxy3-(hydroxymethyl)-2-cyclohexen-1-yl)amino)-a-D-glucopyranosyl-(1–4)-O-a-D-glucopyranosyl-(1-4)-D-glucose. Unlike the sulfonylureas, this oligosaccharide does not enhance insulin secretion, but brings about anti-hyperglycaemic action by competively and reversibly inhibiting pancreatic a-amylase and membrane-bound intestinal a-glucoside hydrolase enzymes. Until now, there is paucity of information on studies aimed at correcting for increased body fat deposition that is consistent with feeding broiler-chickens low-protein diets. The need for such studies is compelling, because inspite of the benefits to the environment of the concept of feeding low-protein, amino acid-supplemented diets, it is unlikely to command wider commercial acceptability if the problem of increased carcass fatness persists. This need forms the major basis for the design of the present study which investigates the effect of low-protein amino acid-supplemented diets in combination with the inclusion of two levels of CLAs or an glucosidase inhibitor, respectively.