Two drying methods of bovine faeces for estimating n-alkane concentration, intake and digestibility: A comparison

An experiment was completed to evaluate effects of two drying methods applied to faecal and herbage samples on estimation of n-alkane concentration and the calculated dry matter (DM) intake, faecal output (FO) and apparent in vivo DM digestibility (DMD). Four Holstein–Friesian steers (182 ± 12.1 kg initial body weight) housed in individual pens were fed at 8:30 and 16:30 h with ryegrass (Lolium perenne L.) hay for 18 d. Refusals were removed and weighed every day at 8:30 h before morning feeding. From days 9 to 18, the steers were dosed twice a day at feeding time, with cellucotton stoppers containing C32 (88.49 mg/pellet) and C36 (87.12 mg/pellet). During the last 5 d of dosing, total collection of faeces was completed using harnesses. For the n-alkane analysis, faecal (n = 64) and offered hay (n = 4) samples were subdivided into two subsamples and prepared for two alternative drying methods: oven-drying at 60 °C (OD) or freeze-drying (FD). The n-alkane profiles of the offered and refused hay oven-dried at 60 °C did not differ. In offered hay subsamples, concentrations of n-alkanes were not affected by drying method. In faecal subsamples, drying method affected (P<0.05) concentrations of all n-alkanes, except for C23, C25 and C35, as well as the ratios C32:C31 and C32:C33. There were no differences between estimated and measured values when DM intake and apparent in vivo DMD were estimated based on the ratio C32:C33. In contrast, when the ratio C32:C31 was used, estimated values either differed (P<0.02) or tended to differ (P<00.09) from measured values for OD and FD subsamples, respectively. Estimates of FO from subsamples OD and FD did not differ from measured values. Faecal recovery increased with increasing carbon-chain length in both drying methods. Results show that oven-drying at 60 °C could replace freeze-drying for sample dehydration to estimate DM intake and apparent in vivo DMD when ratio C32:C33 was used. However, due to the low number of replicates, further studies should be conducted before use of C32:C33 ratio in oven-dried samples can be recommended.