The effect of fermentable nitrogen availability on in vitro gas productionand degradability of NDF

Effects of harvesting ruminal micro-organisms from ruminal fluid on pattern s of gas production were investigated in experiment 1 by incubating 200 mg DM of pure cellulose, oatfeed, ryegrass, cocksfoot, wet and dry season kiku yu grasses with either diluted ruminal fluid or harvested ruminal bacteria. Gas production degradability parameters obtained from fitting the data to the model Gas = B(1 - exp(-C(t-lag))) after correcting gas volumes for the fermentation of soluble material did not differ between these two treatment s. In experiment 2, the effect of ammonia concentration on the digestibilit y and gas production degradability parameters of NDF prepared from cellulos e, guinea, star grass, Brachiaria decumbens and wet season kikuyu grass was studied using harvested ruminal bacteria as the inoculant. An ammonia conc entration of 25 mg N/1 was sufficient to enable the maximum digestibility o f NDF whilst one of between 50 and 100 mg N/1, depending on the availabilit y of fermentable NDF, was necessary to achieve the potential rate of NDF fe rmentation. (C) 2000 Elsevier Science B.V. All rights reserved.