Digestion capasity, nutrient digestibilities and physico-chemical conditions in the intestine influenced by the age of growing turkeys

Six experiments have been conducted to examine digestibility and feeding value of domestic Finnish fibre-rich cereals (barley and oats as compared to maize and wheat) and protein sources (rapeseed meal and cake, peas, faba beans, lupin seeds) for growing turkeys and to investigate effects of age of the birds (from 3 to 12 weeks of age) on digestion process and estimated nutrient digestibility and energy values. Besides, an objective of the study was to test applications of digestibility research methodology for turkeys. Total tract digestibility and apparent metabolizable energy (AME) was assayed in experimental cages using excreta collection, and a slaughter method was applied to sample small intestinal digesta for determination of apparent ileal crude protein digestibility (AICPD), jejuno-duodenal digesta viscosity and caecal volatile fatty acid (VFA) concentration. Digesta viscosity decreased and caecal VFA production increased with age of growing turkeys. Digesta retention times in the small intestine were generally longer in the older birds than in the younger ones. Crude fat digestibility and AME increased with age of growing turkeys, especially with viscous diets. AICPD seemed to decrease with age in most cases. Supplementation with β-gucanase-xylanase decreased viscosity, improved crude fat digestibility and metabolizable energy value and increased VFA production especially in barley-fed turkeys and especially in the young birds. Poor protein digestibility and low energy value of rapeseed meal and rapeseed cake decreased their feeding value for turkeys. In addition, a typical goitrogenic effect of rapeseed feeding was detected. Use of legume seeds as feed for growing turkeys is limited mostly by the low energy value in lupin seeds and the low ileal protein and amino acid digestibility in faba beans. Digestibility of fibre-rich protein sources was not improved with age of the turkeys. Euthanizing the turkeys for AICPD determination by carbon dioxide and bleeding led to lower digestibility values than mechanical stunning and cervical dislocation, suggesting inferiority of carbon dioxide stunning in experimental use. Comparison of AICPD and AME results obtained using different markers showed that considerable differences may occur, especially on total tract level, when acid-insoluble ash gave considerably lower AME values than titanium dioxide and chromic oxide. LIST OF ORIGINAL PUBLICATIONS This thesis is based on five research articles referred to by Roman numerals: I Palander, S. , Nasi. M. & Valkonen, E. 2005. Effect of age of growing turkeys on nutrient digestibility and energy value of cereal-soybean-based diets. Archives of Animal Nutrition 59:139-147. II Palander, S. , Nasi, M. & Jarvinen, S. 2005. Effect of age of growing turkeys on digesta viscosity and nutrient digestibility of maize, wheat, barley and oats fed as such or with enzyme supplementation. Archives of Animal Nutrition 59:191-203. III Palander, S. , Nasi, M. & Hagg, P. Digestibility and energy value of cereal-based diets in relation to digesta viscosity and retention time in turkeys and chickens at different ages. Submitted manuscript IV Palander, S. , Nasi, M. & Ala-Fossi, I. 2004. Rapeseed and soybean products as protein sources for growing turkeys of different ages. British Poultry Science 45:664-671. V Palander, S. , Laurinen, P., Perttila, S. , Valaja, J. & Partanen, K. 2006. Protein and amino acid digestibility and metabolizable energy value of pea (Pisum sativum), faba fean (Vicia faba) and lupin (Lupinus angustifolius) seeds for turkeys of different age. Animal Feed Science and Technology 127:89-100. The papers I, II, IV and V have been reprinted with the permission of the respective copyright owners Taylor and Francis Ltd. and Elsevier Science. Authors (S. Palander) contribution to the papers: The author has planned and led the practical management of the experiments for papers I  IV, participated in sample collecting and data recording for papers I  V and taken the main responsibility for calculations, statistical analysis, results interpretation and reporting for papers I  V.