In sacco degradation characteristics as predictors of digestibility and voluntary intake of roughages by mature ewes

The in situ nylon bag technique was evaluated as a method of predicting digestibility and voluntary intake of roughages. Twelve feedstuffs including five untreated cereal straws, two cereal straws treated with urea and five grass hays were each offered to six–eight mature non-pregnant and non-lactating ewes (70.4±8.4 kg), ad libitum, over a period of eight weeks. Soyabean meal was given as supplement in variable amounts to cover rumen microbes requirements for degradable nitrogen. Two rumen fistulated rams were used to measure the digestibility of each diet and the kinetics of dry matter (DM) degradation in the rumen of the roughages. Apparent organic matter digestibility (OMD) of the roughages ranged from 0.441 to 0.600 g kg−1 and DM intake from 9.6 to 17.9 g kg−1 of live weight. DM degradation after 96 or 72 h incubation were the best predictors of roughages OMD (r2=0.73 and 0.70, respectively) while prediction of DM intake was most accurate from 3 h DM degradation and ADF content of roughages (r2=0.68 and 0.67, respectively). In contrast, digestible DM intake was best predicted by a multiple regression equation including the degradation constants soluble fraction and rate of degradation accounting for 89% of the variation observed. Live weight variation of ewes was also well predicted from a similar equation or from soluble fraction alone (r2=0.80) but the predictive capability of ADF was higher (r2=0.86) for this purpose.