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

Effects of harvesting ruminal micro-organisms from ruminal ̄uid on patterns of gas production were investigated in experiment 1 by incubating 200 mg DM of pure cellulose, oatfeed, ryegrass, cocksfoot, wet and dry season kikuyu grasses with either diluted ruminal ̄uid or harvested ruminal bacteria. Gas production degradability parameters obtained from ®tting the data to the model Gas ˆ B(1ÿ expÿC…tÿLag†) after correcting gas volumes for the fermentation of soluble material did not differ between these two treatments. In experiment 2, the effect of ammonia concentration on the digestibility and gas production degradability parameters of NDF prepared from cellulose, guinea, star grass, Brachiaria decumbens and wet season kikuyu grass was studied using harvested ruminal bacteria as the inoculant. An ammonia concentration of 25 mg N/l was suf®cient to enable the maximum digestibility of NDF whilst one of between 50 and 100 mg N/l, depending on the availability of fermentable NDF, was necessary to achieve the potential rate of NDF fermentation. # 2000 Elsevier Science B.V. All rights reserved.