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 α-glucosidase inhibitor

The effect of supplemental conjugated linoleic acid (CLA) or Bay g 5421 - an α-glucosidase inhibitor - were investigated with a total of 324 male (ROSS) broiler-chicks from age 3 to 6 weeks using performance, carcass characteristics, whole-body composition and efficiencies of nutrients utilization as the response criteria. The trial comprised 6 (D1-D6) isoenergetic (13.0 MJ kg - 1 ) broiler diets containing 230 (High-protein, HP - D1) or 180 g kg - 1 (Low-protein, LP - D2) crude protein supplemented with essential amino acids (EAAs) to meet the minimum National Research Council's specifications. Diets 3 and 4 were derived from the LP diet, ie D2, by the respective supplementation of 20 or 40 g kg - 1 CLA-enriched oil containing mainly the cis-9, trans-11 (34.2%) and trans-10, cis-12 (34.0%) isomers while diets 5 and 6 were similarly derived from D2 by the respective supplementation of 50 or 100 mg kg - 1 Bay g 5421. Reducing dietary crude protein from 230 g kg - 1 in Dl (ie HP control) to 180 g kg - 1 in D2 (LP control) had no significant effect on weight gain (WG), feed consumption (FC) or feed conversion efficiency (FCE). However, the LP group consumed 6% more feed than the high protein group. CLA supplementation had no significant effect on WG, FC, or FCE while Bay g 5421 significantly (P ≤ 0.05) reduced WG (18%), increased FC (23-28%) and depressed FCE (30-57%) relative to the control in a dose-related fashion. Neither the reduction in crude protein nor the supplementation of either CLA or Bay g 5421 significantly affected the relative weights of the breast or thigh although 100 mg kg - 1 of the inhibitor level reduced the carcass weights by 9-10%. Amongst the organs weighed, only the liver and abdominal fat pad were significantly (P < 0.05) affected. CLA supplementation in the LP diet caused about 22% increase in liver weight while the abdominal fat pad was unchanged. Conversely, Bay g 5421 supplementation completely reversed the increased liver and abdominal fat weights in the LP diet to the HP control levels. Whole-body composition (g kg - 1 fresh weight or dry matter) was unaffected by feeding 230 or 180 g kg - 1 protein except for total body fat which was increased by 28% in the LP diet (110.2 ′ 8.7 vs. 140.7 ′ 9.1 g kg - 1 ). CLA supplementation in the LP diet had no significant effect on whole-body composition. Conversely, Bay g 5421 significantly (P < 0.01) decreased carcass dry matter (ie, increased body water by 7-8%) and reduced total body fat by about 45% (ie, 140.7 ′ 9.1 vs. 77.5 ′ 5.6 g kg - 1 ) to a value 70% of the HP control. On a moisture-free basis, Bay g 5421 caused a 15-17% increase (ie, 512.6 vs. 600.0 g kg - 1 DM) in whole-body protein while CLA had no significant effect. Only Bay g 5421 significantly (P < 0.05) increased protein: fat ratio (1.3: 1 vs. 2.5: 1) implying a strong fat-to-lean mass partitioning effect. CLA supplementation in the LP diet had no influence on energy retention and did not correct for the increased fat retention (deposition). It also had no effect on N-excretion. Conversely, Bay g 5421 significantly (P ≤ 0.05) decreased energy and fat retention but increased N- and faecal starch excretion in a dose-related manner. It was concluded, that under low-protein, amino acid-supplementation and isoenergetic feeding regimens, Bay g 5421 is far more potent than CLA to change body composition in broiler-chickens.