Comparison of the bioavailability of lysine in blood meals of various origins to that of l-lysine HCL for rainbow trout (Oncorhynchus mykiss)

The bioavailability of lysine in blood meals from various origins was examined in rainbow trout. Bioavailability of lysine of the blood meals was assessed in comparison to that of l-lysine HCL using a slope ratio assay experimental design. A corn gluten meal-based diet, deficient in lysine (1.5% diet), was used as the basal diet. Two levels of spray-dried poultry blood meal (SDBM), flash-dried bovine blood meal (FDBM), disc-dried poultry blood meal (DDBM), and lysine-HCL substituted corn gluten meal in the basal diet to produce experimental diets containing 1.8 or 2.2% lysine. These diets were pair-fed to rainbow trout (initial body weight = 25 g/fish) reared at 15 °C for 12 weeks. Weight gain, feed efficiency ratio (FER, gain: feed), retained nitrogen (RN), and recovered energy (RE) increased significantly (P < 0.05) with increasing lysine levels. Diets containing SDBM and FDBM recorded significantly greater weight gain, FER, RN and RE compared to DDBM (P < 0.05). At the 1.8% lysine level, the diet containing FDBM recorded significantly greater weight gain, and RN than the diet supplemented with l-lysine HCl. The weight gain, FER and RN of the fish fed diets containing SDBM was not significantly different from that of the fish fed the diets with l-lysine HCl, at both lysine levels. At the 2.2% lysine level, feeding diets containing FDBM and DDBM resulted in significantly lower weight gain than diet supplemented with l-lysine HCl, suggesting that other nutrients may have become more limiting than lysine at high levels (20%) of blood meal. Results suggest that the bioavailability of lysine in SDBM or FDBM is slightly greater than that of l-lysine HCL. Bioavailability of lysine in the DDBM used in this study appeared to be significantly lower than that of spray-dried or flash-dried blood meals.