The dacron bag technique for comparing rumen degradability of untreated and ammonia-treated barley straw – effect of particle size and degree of replication

Abstract

SUMMARYSix rumen-fistulated steers were studied over six periods of 3 days at Reading University's Animal Production Research Unit. In each period, eight dacron bags comprising two replicates of the 22 factorial treatment set consisting of untreated and NH3-treated barley straw in chopped (12–54 mm) or ground (2·5 mm screen) form were placed in the rumen of each steer. Bags were left in the rumen for a given time which was one of the set 6, 9, 15, 24, 48, 72 h. Percentage dry matter (DM) disappearance from dacron bags was consistently higher for NH3-treated than untreated straw and higher for ground than chopped straw. Analysis of variance gave F ratios for period and steer which were non-significant but of similar size, showing that using fewer animals could be compensated for by using more periods. Percentage DM disappearance as a function of time was well described by the model y = a — beet. The parameter defining rate of disappearance c, was similar for the four forms of straw. Differences between straws occurred in values of a (potential degradability) and b suggesting that physical form of material put into dacron bags needs standardizing if absolute values of a are to be used (e.g. for predicting roughage intake). Experimental designs need further research.