Effect of bag type on the apparent digestibility of feeds in ANKOM DaisyII incubators

This study determined if the in vitro apparent dry matter digestibility (DMD) of feed samples in ANKOM DaisyII incubators is affected when alternatives to ANKOM F57 bags are used, or when samples are weighted to ensure submersion in the media. In three experiments, feed samples were incubated within filter bags for 48 h in buffered rumen fluid and for a further 48 h in acidified pepsin in ANKOM DaisyII incubators. In Experiment 1, 32 replicates of three dried, ground (1 mm) feed samples were either weighed into ANKOM F57 polyester/polyethylene bags with a pore size of 25 μm or weighed into dacron bags with a pore size of 50 μm. One 5 g glass ball was placed in each of eight ANKOM bags or eight dacron bags for each forage to ensure submersion in the media. In Experiments 2a and 2b, 16 and 8 replicates of 14 dried, ground feed samples were respectively, weighed into either ANKOM F57 bags or polyester/polyethelene bags with a pore size of 30 μm. The DMD of these samples was also determined simultaneously using the conventional, tube based, rumen fluid pepsin technique. Regression relationships were derived between ANKOM and alternative bag DMD estimates. In Experiment 1, weighted bags had greater (P < 0.001) digestibility values than unweighted bags. In all the experiments, DMD differed with forage type and bag type (P < 0.001) and there was a bag × forage interaction (P < 0.001). Digestibility values obtained in the alternative bags were consistently higher (P < 0.001) than those obtained in ANKOM bags. Though there was a bag × forage interaction (P < 0.001), there was no bag × weight interaction (P = 0.223). The precision of predicting conventional measurements from ANKOM bag measurements was greater (r2 adj. = 77.3; R.S.D. = 53.2) than that from the alternative bag measurements (r2 adj. = 60.1; R.S.D. = 70.6). Different digestibility estimates are obtained when alternatives to ANKOM F57 bags are used in ANKOM DaisyII incubators. ANKOM bags gave more precise predictions of tube based, conventionally determined digestibility estimates.