Diurnal patterns in rumen volume and composition of digesta flowing into the duodenum

Abstract

Abstract Rate of passage of digesta out of the rumen is generally assumed to follow first order kinetics but this assumption may not hold within 24-h feeding cycles. Four lactating cows offered a mixed forage/concentrate diet ad libitum from 08.00 h to 00.00 h and a protein-rich meal at either 08.30 or 00.30 h were used to investigate diurnal patterns in rumen volume and composition of digesta flowing into the duodenum. Cows were fitted with large rumen cannulae to permit complete emptying of rumen digesta and T-piece duodenal cannulae with inserts to enable collection of representative samples of digesta. Chromium-mordanted lucerne hay manually dosed to the rumen at 2-h intervals and a continuous infusion of cobalt-EDTA were used as digesta flow markers. Duodenal digesta was sampled over three alternate days to obtain samples representing every hour of the 24-h day, which were analysed individually. Use of either of the two markers gave similar results for mean daily flow but not for hourly flow and thus hourly flow data were not considered reliable. The content of crude protein in duodenal digesta varied within one feeding cycle from 200 to 320 g/kg in cows offered protein at 08.30 (‘day’) and from 240 to 300 in cows offered protein at 00.30 h (‘night’). On a daily basis, fractional passage rates (calculated from duodenal flow divided by rumen pool size) were significantly (P = 0·016) lower for protein for ‘night’ (0·0750 per h) versus ‘day’ (0·0824 per h) cows. The observation that marked diurnal patterns in the composition of protein flowing into the duodenum can apparently be ‘smoothed’ simply by altering feeding sequence, which was correlated with an increased milk fat yield, suggests there is potential for improving production through manipulating the way in which dietary components are offered within a day. Rate of passage of digesta out of the rumen is generally assumed to follow first order kinetics but this assumption may not hold within 24-h feeding cycles. Four lactating cows offered a mixed forage/concentrate diet ad libitum from 08.00 h to 00.00 h and a protein-rich meal at either 08.30 or 00.30 h were used to investigate diurnal patterns in rumen volume and composition of digesta flowing into the duodenum. Cows were fitted with large rumen cannulae to permit complete emptying of rumen digesta and T-piece duodenal cannulae with inserts to enable collection of representative samples of digesta. Chromium-mordanted lucerne hay manually dosed to the rumen at 2-h intervals and a continuous infusion of cobalt-EDTA were used as digesta flow markers. Duodenal digesta was sampled over three alternate days to obtain samples representing every hour of the 24-h day, which were analysed individually. Use of either of the two markers gave similar results for mean daily flow but not f or hourly flow and thus hourly flow data were not considered reliable. The content of crude protein in duodenal digesta varied within one feeding cycle from 200 to 320 glkg in cows offered protein at 08.30 day’) and from 240 to 300 in cows offered protein at 00.30 h (‘night’). On a daily basis, fractional passage rates (calculated from duodenal flow divided by rumen pool size) were significantly (? = 0·016) lower for protein for ‘night’ (0·0750 per h) versus ‘day’ (0·0824 per h) cows. The observation that marked diurnal patterns in the composition of protein flowing into the duodenum can apparently be ‘smoothed’ simply by altering feeding sequence, which was correlated with an increased milk fat yield, suggests there is potential for improving production through manipulating the way in which dietary components are offered within a day.