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 investigate the fermentability of poor quality natural pasture (veld) hay mixed with different amounts of Napier hay or groundnut hay. In vitro fermentations were conducted in nitrogen-rich (NR) and nitrogen-free (NF) media. Groundnut hay was more rapidly fermented than Napier hay, the nitrogen content of the medium making little difference to the fermentation characteristics of either hay. Veld hay was the least fermentable substrate, particularly when NF medium was used. Statistically significant positive interactive effects were observed between both supplements and veld hay fermented in both media as gauged by gas production and dry matter disappearance. Evidence of significant interactions had not been obtained from earlier measurements of in vivo digestibility using the same feeds, but they may have been obscured by increased rates of passage with increased supplementation. Differences between gas productions in NR and NF media were explored as possible indicators of nitrogen deficiency in feed mixtures. Both Napier hay and groundnut hay appeared to be balanced in terms of energy and nitrogen fermentable by rumen microbes.