Digestibility, growth and excretion response of rainbow trout (<i>Oncorhynchus mykiss</i>Walbaum) to feeds of different ingredient particle sizes

Abstract

The effects of feed ingredient particle size on apparent digestibility, growth and excretion responses of rainbow trout were investigated in pilot production systems. Particle size of the feed ingredients (ground using a hammer mill with 0.6 and 3.0 mm screen sizes) had no significant effect (P > 0.05, d.f. = 1/6) on the apparent digestibility of dry matter, phosphorus and crude protein in cold-extruded diets. Feed ingredient particle size had an impact on the feed conversion ratio over an 85-day feeding trial when key ingredients (78.65% of diet) were ground using a pulverizer and a hammer mill with 3.0 mm screen size and heat extruded. No significant differences (P > 0.05, d.f. = 1/12) were observed in the excretion ratios of TAN (total ammonia nitrogen), TKN (total Kjeldahl nitrogen), TP (total phosphorus), BOD5 (5-day biochemical oxygen demand) and TSS (total suspended solids) among three feed types, which included a wide ingredient particle size distribution.