Nutrient digestibility and protein quality of oats differing in chemical composition evaluated in rats and by an in vitro technique

The relationship between a number of chemical components and the nutritive value of 15 oat samples was studied in vivo with rats and in vitro with an enzymatic method. Also the effects of varying crude protein (CP) content of oat samples on amino acid (AA) pattern and protein quality were studied. The content of total fibre was calculated as the residual fraction after substraction of the analysed content of sugars, starch, CP, crude fat and ash from the dry matter content. There were significant negative correlations (r = −0.52 to −0.74) between total fibre and in vivo true N digestibility (TND), digestibility of energy (DE)(P < 0.01), biological value (BV) and net protein utilisation (NPU) (P < 0.05). Positive correlations (r = +0.61 to +0.65) were also found between starch content and BV (P < 0.05) and NPU (P < 0.01). The in vitro total tract DM digestibility and in vitro ileal DM digestibility were negatively correlated to total fibre (P < 0.01) and positively correlated to starch content and DE (P < 0.01), respectively. The in vitro total tract and ileal CP digestibility correlated positively to levels of CP (P < 0.05 and P < 0.001, respectively) and soluble β-glucans (P < 0.001 and P < 0.01, respectively). There were significant relationships between CP of oats and the content in CP of cysteine, methionine + cysteine, histidine (P < 0.001), serine, glycine (P < 0.01), aspartic acid and tyrosine (P < 0.05). However, with the exception of phenylalanine (P < 0.05), the variation in AA composition did not affect BV.