Effect of dietary protein level, amino acid balance and feeding level on growth, gastrointestinal tract, and mucosal structure of the small intestine in broiler chickens

Anim. Res. Effect of dietary protein level, amino acid balance and feeding level on growth, gastrointestinal tract, and mucosal structure of the small intestine in broiler chickens Harry Kofi SWATSON 2 Robert GOUS 2 Paul Ade IJI 0 ZARRINKALAM 1 0 Present address: School of Environmental Development & Agriculture , Technikon Free State, Private Bag X20539 , South Africa 1 Department of Animal Science, The University of Adelaide , Roseworthy 5371 , Australia 2 Discipline of Animal & Poultry Science, University of Natal , Private Bag X01, Scottsville 3209 , South Africa - In a factorial experiment, two series of feeds containing excess dietary protein, differing in amino acid balance (i.e. balanced (BPS) and unbalanced (UPS) amino acid mixture), and with a range of protein contents (400, 300 and 200 g CP·kg-1) at the same energy content of 13 MJ AME·kg-1 were offered at two levels of feeding (ad libitum or 0.75 of ad libitum intake) to 4320 broiler chickens between 10 and 24 days of age. Growth rate was significantly lowered by feed restriction. There was also a significant (P < 0.001) effect of dietary protein on the combined weight of the proventriculus and gizzard but only for the birds on the restricted feeding regime. Relative pancreatic weight increased (P < 0.001) with an increase in dietary protein level for the birds fed restricted amounts of BPS. The crypt depth of chicks on the ad libitum feeding regime was higher (P < 0.01) for the chicks on the BPS than for those on the UPS diet. The protein content of the jejunal mucosa was higher (P < 0.001) for birds fed ad libitum on the UPS diet than on the BPS diet. Daily feed allocation had a significant (P < 0.01) effect on jejunal protein content in birds that received the BPS diet, this being reduced in birds on restricted feeding. Maltase (P < 0.001) and sucrase (P < 0.01) activities were significantly reduced in chicks offered ad libitum access to the UPS diet. At high dietary CP, the specific activity of alkaline phosphatase was lower (P < 0.001) in chicks on the UPS diet than in those fed the BPS diet. - Résumé — Effets de la concentration en protéines, de l’équilibre en acides aminés et du niveau d’ingestion de l’aliment sur la croissance, le développement du tube digestif et la structure de la muqueuse jéjunale chez le poulet de chair. Six aliments isoénergétiques (13 MJ EMa·kg–1) selon le plan factoriel : 3 concentrations en protéine brute (400, 300 et 200 PB g·kg–1) × 2 équilibres en acides aminés (BPS = équilibré, UPS = déséquilibré par rapport aux besoins), ont été offerts à deux niveaux d’ingestion (ad libitum ou 75 % de l’ad libitum) à 4320 poulets de chair entre 10 et 24 jours d’âge. La vitesse de croissance était significativement réduite par la restriction alimentaire. Un effet du taux protéique sur le poids combiné du proventricule et du gésier était significatif (P < 0,001) mais uniquement chez les poulets restreints. Le poids relatif du pancréas augmentait (P < 0,001) avec la concentration du régime protéines BPS chez les poulets restreints. La profondeur des cryptes des villi de l’intestin était plus profonde chez les poulets nourris ad libitum avec les régimes BPS par rapport aux régimes UPS (P < 0,01). La concentration en protéine de la muqueuse jéjunale était supérieure chez les poulets consommant ad libitum les régimes UPS par rapport à ceux ingérant les régimes BPS (P < 0,001). La restriction alimentaire réduisait également la teneur en protéine du jéjunum (P < 0,01) chez les poulets consommant les régimes BPS. Les activités maltase (P < 0,001) et sucrase (P < 0,01) étaient significativement inférieures chez les poulets consommant ad libitum les régimes UPS. A haute teneur en protéine, l’activité spécifique de la phosphatase alcaline était réduite (P < 0,001) chez les poulets consommant les régimes UPS par rapport à ceux recevant les régimes BPS. poulet de chair / excès de protéine / restriction alimentaire / enzyme / tube digestif 1. INTRODUCTION The synthesis of protein, i.e. protein deposition in broiler chickens, is a process that requires a large amount of energy and is to some extent dependent on bird-related factors such as the development of the gastrointestinal tract (GIT) [ 30 ]. Apart from the commonly assessed effects of the energy to protein ratio (E:P ratio) on the biological performance of broiler chickens, the study of causal connections at the GIT/organ level has been largely ignored or underestimated. The efficiency of utilisation of dietary nutrients partly depends on the development of the gastrointestinal tract. Such development can be assessed through measurements of the crypt, a region in which new intestinal cells are formed; villus height and surface area, to determine the area available for digestion/absorption, and the activities of membrane-bound digestive enzymes of the small intestine. Such assessment has been routinely done in poultry [ 2, 17, 18, 38 ] but the results have not been adequat (...truncated)