Prediction of in vivo dry matter, organic matter, and energy digestibilities of silage in in vitro digestion techniques

Twenty experimental silages were made from seven pasture species at different stages of maturity. In vivo dry matter, organic matter, and energy digestibilities of the silages were determined at restricted and ad libitum intake levels on standardized pairs of Merino wethers. In vitro dry matter digestibility determinations were made on ground frozen silage and ground oven-dried silage with and without a correction for the loss of volatile compounds during drying. Corrected in vitro dry matter digestibilities of ground oven-dried silage for a 48 hr rumen liquor digestion time gave the most accurate prediction of in vivo dry matter (r = 0.88), organic matter (r = 0.86), and energy (r = 0.74) digestibilities for restricted intake levels. In vitro digestibilities of ground frozen silage more accurately predicted in vivo digestibilities than did in vitro digestibilities of ground oven-dried silage without the correction for volatile losses. In vivo dry matter and organic matter digestibilities were highly correlated (v = 0.97), but both were poorly correlated with in vivo energy digestibilities. In vitro digestion of ground oven-dried silage with a correction for the volatile compounds lost during drying is recommended as a suitable routine determination for predicting the in vivo digestibility of silage.