Assessing the Bioavailability of Synthetic Methionine and Lysine from Different Sources in Rainbow Trout (Oncorhynchus mykiss).

Abstract

Relative bioavailability of L-methionine and a hydroxy methionine analogue (MHA-Ca) were compared to the commercially prevalent DL-methionine in a 12-week growth trial. A separate 12-week trial investigated relative bioavailability between L-lysine HCL and L-lysine sulphate. Basal diets were formulated to be deficient in methionine or lysine and were supplemented with increasing equimolar levels of methionine or lysine from three sources of methionine or two sources of lysine. Using a linear slope-ratio assay, bioavailability of L-methionine and DL-methionine were determined to be similar (p>0.10). Differences in bioavailability between DL-methionine and MHA-Ca were observed (p<0.05), with MHA-Ca being 69, 60 and 73% as bioavailable as DL-methionine based upon weight gain, growth rate (thermal-unit growth coefficient) and retained nitrogen response parameters respectively. L-lysine HCL and L-lysine sulphate were effective sources of lysine with no significant differences in bioavailability (p>0.10). In conclusion, differences in bioavailability exist between sources of synthetic methionine, but not lysine.