Effects of carrier matrix and dosing frequency on digestive kinetics of even-chain alkanes and implications on herbage intake and rate of passage studies

Abstract

An experiment was carried out to investigate the digestive kinetics of various even-chain alkanes adsorbed into different carrier matrices and to assess their potential use to estimate faecal output, herbage intake and rate of passage in goats. The carrier matrices (alkanes) tested were cellulose powder (C-24 and C-28 alkanes), paper bungs (C-26 alkanes), Gilson paper filters (C-30 alkanes) and shredded paper (C-32 alkanes). Effects of carrier matrix and dosing frequency (once or twice daily) on diurnal fluctuations of faecal marker concentrations were simulated by modelling the faecal excretion curves of each marker. C-32 alkanes adsorbed into shredded paper showed the longest transit time (TT) and the slowest fractional outflow rate from a fast compartment (k(2)) and consequently a greater total mean retention time (TMRT) than the other markers. In contrast, both C-24 and C-28 alkanes absorbed into cellulose powder showed the fastest k(2) and the shortest TT and TMRT. Our results suggest that relative differences in rate of passage associated with different nutritional treatments can be investigated using even-chain alkanes as rate of passage markers for comparative studies. Faecal outputs measured or estimated Using C-28, C-30 or C-32 alkanes as external markers were not significantly (P > 0.05) different, but the accuracy of estimation was higher with C-28 and C-32 alkanes (r = 0.81 and 0.83 respectively). On average, faecal output was significantly (P < 0.05) overestimated by 31% (SEM 9.4) and 3S% (SEM 11.2) with C-24 and C-26 alkanes respectively. There were no significant (P > 0.05) differences between observed and estimated herbage intakes when pairs C-31/C-30 and C-33/C-32 were used, this latter pair of alkanes giving the best prediction. With the other alkane pairs (C-25/C-24, C-27/C-26 and C-29/C-28), estimates were biased, although actual and predicted values were significantly (P < 0.05) correlated. The simulation study revealed that, when markers were dosed twice a day, there were no significant (P > 0.05) differences between even-chain alkanes in the amplitude of the diurnal fluctuation of their faecal concentrations. However, when the marker administration was as a single dose per day, C-32 alkane absorbed into shredded paper resulted in the narrowest range of variation, with no significant differences among the other carrier matrices.