Prediction of forage digestibility in ruminants using in situ and in vitro techniques

Two experiments were completed to determine the in vivo digestibility of organic matter (OMD) of forages in sheep. The first experiment was done with 12 forages (database 12) consisting of fresh and conserved forms of lucerne, red clover, orchard grass and perennial ryegrass, fed restricted to sheep. The second experiment was done with 98 forages fed ad libitum to sheep, divided in a database with 37 forages (database 37) with similar qualities as database 12 and a database with 61 forages (database 61). OM and DM digestibility of the forages from these databases was also determined with the in situ nylon bag technique, the pepsin–cellulase technique, the technique of Tilley and Terry and the gas production technique. Database 37 was used to find relationships between OMD and the alternative techniques and between OMD and chemical composition. Databases 12 and 61 were used to validate the observed relationships. The databases were also used to find out if there was an effect of DM intake on the relationships. The OMD predictions by the alternative techniques improved and the effect of DM intake disappeared upon the inclusion of a chemical parameter. The prediction by the in situ technique plus crude protein content showed highest accuracy in the validations, although the four alternative techniques showed similar potency in predicting OMD. The choice of the technique for prediction also depends on other factors, such as animal welfare, price, time, experience and additional information on feed degradation.