THE DACRON BAG TECHNIQUE FOR COMPARING RUMEN DEGRADABILITY OF UNTREATED AND AMMONIA-TREATED BARLEY STRAW - EFFECT OF PARTICLE-SIZE AND DEGREE OF REPLICATION

Six 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 2(2) factorial tre atment set consisting of untreated and NH3-treated barley straw in cho pped (12-54 mm) or ground (2.5 mm screen) form were placed in the rume n of each steer. Bags were left in the rumen for a given time which wa s one of the set 6, 9, 15, 24, 48, 72 h. Percentage dry matter (DM) di sappearance from dacron bags was consistently higher for NH3-treated t han untreated straw and higher for ground than chopped straw. Analysis of variance gave F ratios for period and steer which were non-signifi cant but of similar size, showing that using fewer animals could be co mpensated for by using more periods. Percentage DM disappearance as a function of time was well described by the model y = a-be(-ct). The pa rameter defining rate of disappearance c, was similar for the four for ms of straw. Differences between straws occurred in values of a (poten tial degradability) and b suggesting that physical form of material pu t into dacron bags needs standardizing if absolute values of a are to be used (e.g. for predicting roughage intake). Experimental designs ne ed further research.