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The present study assessed the effect of different feed ingredients on nutrient apparent digestibility coefficients (ADC), nitrogen/energy balance and morphology changes in the intestine of Nile tilapia; using a control diet and six test diets, in which the following six ingredients were included at 30%: hydrolysed feather meal (HFM), soybean meal (SBM), rice bran (RB), rapeseed meal (RM), sunflower meal (SFM) and dried distillers grains with solubles (DDGS). The proximal, middle and distal intestine was processed for quantitative histology counting the number of goblet cells (GC), and measuring the thickness of lamina propria (LP) and submucosa (SM). The study showed that the ADC of protein in raw materials were highest in SBM (92.2%), followed by SFM (90.2%), DDGS (89.2%), RM (87.8%), HFM (86.9%) and RB (84.0%). The nutrient ADCs had no correlation with intestinal morphology changes. Only the SBM diet caused noticeable changes in intestinal morphology such as an increase the thickness of SM and LP and the number of GC. The diet composition, however, altered the protein efficiency and the maintenance energy requirement. Protein retention efficiency was the lowest in fish fed HFM and the highest in RB. The highest maintenance energy requirements were observed in HFM and SBM treatments.

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