USE OF AN IN-VITRO GAS-PRODUCTION METHOD TO INVESTIGATE INTERACTIONS BETWEEN VELD HAY AND NAPIER HAY OR GROUNDNUT HAY SUPPLEMENTS

Measurement of gas produced during in vitro fermentation was used to i nvestigate the fermentability of poor quality natural pasture (veld) h ay mixed with different amounts of Napier hay or groundnut hay. In vit ro fermentations were conducted in nitrogen-rich (NR) and nitrogen-fre e (NF) media, Groundnut hay was more rapidly fermented than Napier hay , the nitrogen content of the medium making little difference to the f ermentation characteristics of either hay. Veld hay was the least ferm entable substrate, particularly when NF medium was used. Statistically significant positive interactive effects were observed between both s upplements and veld hav fermented in both media as gauged by gas produ ction and dry matter disappearance. Evidence of significant interactio ns had not been obtained from earlier measurements of in vivo digestib ility using the same feeds, but they may have been obscured by increas ed rates of passage with increased supplementation. Differences betwee n gas productions in NR and NF media were explored as possible indicat ors of nitrogen deficiency in feed mixtures.:Both Napier hay and groun dnut hay appeared to be balanced in terms of energy and nitrogen ferme ntable by rumen microbes. (C) 1997 Elsevier Science B.V.