Effects of phenolic acid structures on meadow hay digestibility

Abstract

The objectives were to evaluate effects of phenolic acid content and composition on the digestibility of six meadow hays from Northern Portugal. Digestibility was assessed by gas production, in vitro and in situ degradation methods. Four cows fed diets at energy maintenance were used for in situ incubations and to provide rumen fluid for in vitro incubations. There were no relationships between phenolic acid concentrations and other cell wall components. The dry matter (DM) potential degradation ( a + b) was positively related to the etherified fractions of ferulic acid (FAeth, P=0.012) and p-coumaric acid (PCAeth, P<0.001) and to the total amount of ferulic acid (FAtotal; P=0.033). The insoluble, but potentially degradable, constant ( b) of DM had a positive relationship with PCAeth (P=0.008). The in vitro neutral detergent fibre digestibility (IVNDFD), and the estimated asymptotic gas production of the second phase ( A 2), were positively related to the esterified fraction of ferulic acid (FAest, P<0.05), FAeth (P<0.01) and FAtotal (P<0.05). The total amount of p-coumaric acid (PCAtotal) had a positive relationship with IVNDFD (P=0.047). In vitro DM digestibility (IVDMD) was positively correlated with FAeth and FAtotal (P<0.05). In contrast, lignin (pm) concentrations negatively correlated with DM effective degradability (ED; P=0.005) and the maximum rate of gas production of the second phase ( R max G 2; P=0.009). Degradation kinetic constants i. e., (c) of DM and NDF tended to be negatively correlated to the phenolic acid concentrations, mainly with the PCAeth fraction (P=0.056 and P=0.006, respectively). The same trend occurred for the fractional rate of fermentation of the second phase ( R 2; P=0.09). Principal component analysis confirmed that lignin (pm) concentration (principal component 3) is one of the major limiting factors to in vitro DM digestibility of these hays. Thus it seems that for these meadow hays, both lignin (pm) content and cross-linkages between cell wall polymers influenced rate and extent of DM degradation.