Estimation of intake and digestibility of silage by beef steers using a controlled release capsule of n-alkanes

Twelve beef steers were fed a grass-legume silage either ad libitum or at 70% of ad libitum feeding. Intake and digestibility were measured directly or predicted using the alkane ratio technique. The C32 and C36 alkanes were delivered via a controlled release capsule (CRC) in the rumen. Level of feeding had no effect on digestibility (P > 0.05) but dry matter (DM) intake tended to be greater for steers fed ad libitum (P = 0.08). The release of alkanes from the CRC was erratic and 20% greater than expected. This influenced the exogenous to endogenous alkane ratios. Estimates of intake were therefore derived using both the expected and actual (determined from total collection of feces and their alkane analysis) exogenous alkane release rates. Estimated intakes based on the manufacturers’ release rate were underestimated and associated with high standard errors. For cattle fed restricted silage, estimated intakes obtained with C31:C32, C33:C32 and C33:C36 alkane pairs and using actual measured release rates ...