Disulphide bonds and cross‐linked amino acids may affect amino acid utilization in feather meal fed to rainbow trout ( Oncorhynchus mykiss )

A digestibility trial was carried to assess the apparent digestibility coefficient (ADC) of crude protein (CP) and amino acids (AA) in two feather meals (FeM) of different origin (FeM1 and FeM2) and in their enzymatically pre‐treated ingredient stream (PTFeM1 and PTFeM2) in rainbow trout. The ADC of CP was 11%–17% higher (p   0.05) of ADC of CP among FeMs and among PTFeMs. The FT‐Raman analysis showed a reduction in concentration and conformational stability of disulphide bonds in the PTFeMs when compared to their FeM counterparts. Moreover, important discrepancies in disulphide concentration were observed between FeMs and between PTFeMs. These observations suggest that the ADC of CP in FeM is not only governed by disulphide bond content and other variables should be considered. Higher concentrations of the cross‐linked amino acids (CLAA) lanthionine, lysinoalanine and β‐aminoalanine were measured in FeM1 and PTFeM1 as compared to FeM2 and PTFeM2 respectively. Previous studies have suggested inverse relationships between CLAAs and the digestibility as well as bioavailability of AAs in feed ingredients. A previous study conducted in our laboratory showed a lower (p < 0.05) bioavailability of arginine in FeM1 and PTFeM1 than in FeM2 and PTFeM2, respectively, in rainbow trout. Our results suggest that (a) the digestibility of AAs in FeM may be affected by disulphide bond content and the presence of CLAAs, and (b) CLAA content may be indicator of bioavailability of AAs in FeM.