Influence of the proportion of poultry slaughter by-products and of untreated or hydrothermically treated legume seeds in diets for rainbow trout, Oncorhynchus mykiss (Walbaum), on apparent digestibilities of their energy and organic compounds

Apparent digestibilities (D) of energy and proximate nutrients were determined in rainbow trout, Oncorhynchus mykiss (Walbaum), by stripping faeces and using Cr₂O₃ as a marker. When wheat gluten + L-lysine-HCl (WG-lys) as sole source of dietary N were increased stepwise from 324 to 941 g·kg^?1, replacing 210 g·Kg^?1 fish oil (FO) and 407 g·kg^?1 gelatinized corn starch (GCS), D of crude protein rose from 96 to 99% and that of FO was always above 96%. D of GCS was 70% at inclusions up to 210 g·kg^?1, but only 41 at 407 g·kg^?1. Three by-products of poultry slaughtering and three legume seeds replaced WG at levels of 250 and 500 g·kg^?1 in a basal diet of WG-lys, minerals and vitamins. Soy beans had been pressure cooked at one of two intensities, and field beans and fields peas were either untreated or had been autoclaved. D of energy and crude protein was hardly affected by dietary proportion in poultry blood mean (84 and 85%), poultry offal meal (80 and 81%) and incompletely pressure cooked soy beans (82 and 90%); increasing dietary proportions from 250 to 500 g·kg^?1 reduced the respective values of feather meal (88–81 and 86–83%), raw (43–32 and 76–70%) and autoclaved field beans (67–57 and 89–86%), as well as raw (47–39 and 86–83%) and autoclaved field peas (65–40 and 91–86%). At the higher proportion, D of energy of completely pressure cooked soy beans was reduced from 91 to 86%, but that of crude protein was constant at 94%.