Effects of the source of non-fiber carbohydrates on in vitro first order ruminal disappearance kinetics of dry matter and NDF of various feeds

An in vitro experiment was conducted to study the effect of non-fiber carbohydrates (NFC) on ruminal disappearance kinetics of dry matter (DM) and neutral detergent fiber (NDF) of alfalfa hay، wheat bran and unmolassed sugar beet pulp. Non-supplemented or NFC supplemented samples [70 mg/g DM of each feed sample as sucrose (SU) or starch (ST) or SU + ST as 1:1] were incubated in bottles containing 40% rumen fluid medium for 4، 8، 16، 24، 48، and 96 h at 39°C. After each incubation time، unfiltered content was analysed for DM and NDF. Filtered fluid was analysed for ammonia-N concentration. Kinetic disappearance rate was determined using a first order non-linear model. The source of NFC used in the medium containing alfalfa hay caused a significant decrease in DM disappearance (P<0. 01). Feed source، NFC type and incubation time had a significant effect (P<0. 01) on NDF disappearance and ammonia-N concentration. In vitro NDF disappearance of unmolassed sugar beet pulp and wheat bran was significantly (P<0. 01) decreased by supplementing with ST and SU + ST. The indigestible dry matter fraction of alfalfa hay was significantly increased when it was supplemented by NFC (P<0. 05). The rate of DM disappearance of unmolassed sugar beet pulp was also significantly influenced by supplemental NFC (P<0. 05). The fractional rate of NDF disappearance of alfalfa hay and wheat bran exhibited an increase (P<0. 05) in response to adding NFC when compared with the non-supplemented samples. Generally، the results of the present study suggested that in addition to the amount of supplemental carbohydrate fed، the source of supplemental carbohydrate and the basal feed sources might be effective on the effect of supplemental NFC on fiber utilization.