The objective of the present study was to evaluate distillers’ dried grains with solubles (DDGS) as a protein source to rainbow trout (Oncorhynchus mykiss), by studying digestibility and growth measurements. One control diet, totally lacking DDGS, and three test diets were made containing 10 % (low), 31% (medium) and 51 % (high) DDGS respectively on dry matter (DM) basis. The control diet and the test diets were made to be as nutritionally equal as possible. Wheat bran was used to balance the fiber content of the diets. The fish were fed a restricted diet two times a day.
Protein digestibility was higher for fishes fed control- and low diets (>900 g/kg DM) than for fishes fed high diet (P < 0, 01), the group fed medium diet didn’t show any statistical differences. Fat digestibility were the same for control-, low- and medium diets (> 830 g/kg DM), but lower for fishes fed the high diet (P < 0,05). The control group had significantly lower final weight than fishes fed the test diets (P < 0,01), and the medium group had a significant higher final weight than the low group. The daily weight gain and feed conversion rate had the same differences between the groups as the final weight. Fishes fed the medium diet had the lowest feed conversion rate (1,0 g feed/g weight gain). The test diets had a better protein efficiency rate than the control diet.
The amino acid profile of DDGS, and other vegetable protein sources, might limit the amount which could be used in fish feed. In the present study it doesn’t seem as the amino acid profile of DDGS have reduced the growth of the fishes since the group fed the medium diet had a higher daily weight gain and a lower feed conversion rate than fishes fed low- and control diets. A possible explanation to this is that the amino acid profile of DDGS better fits the amino acid requirement of rainbow trout th...
