COMPARISON OF INVITRO GAS-PRODUCTION AND NYLON BAG DEGRADABILITY OF ROUGHAGES IN PREDICTING FEED-INTAKE IN CATTLE

The Hohenheimer gas production test has been adapted to describe the kinetics of fermentation based on the exponential model p=a+b(1-e(-ct)). Ten cereal straws previously fed ad libitum to growing steers and consisting of two varieties of winter barley, two varieties of spring barley and one variety of winter wheat either untreated or treated with anhydrous ammonia, were examined. In vitro gas production was compared with in vivo results and with nylon bag degradabilities; the sources of the gas were determined. Total gas production a+b as described by the exponential equation were correlated with intake (0.88), digestible dry matter intake (0.93 ) and growth rate (0.95) in a multiple regression model. Use of the rate of gas production, c, did not improve the precision of correlation. The gas volume could be explained by the amount of volatile acids produced and their proportions. About 50% of the gas volume consisted of CO2 and CH4 arising from fermentation, the remainder being CO2 released from the buffer solution.