In Vitro Rumen Fermentation of Alternative Feeds Relevant for Dairy Production in an Overgrazed Tropical Area

In overgrazed tropical areas, limited quantity and poor quality of pastures constrain dairy production, creating a need for alternative and complementary feeds. This study in southern Ethiopia therefore assessed local feeds other than the overgrazed pasture using in vitro batch incubation to simulate rumen fermentation. The potential of these feeds as alternatives was evaluated based on rumen fermentation (assessed through total fermentation based on total volatile fatty acids (VFA) and apparent rumen degradable organic matter (ARDOM), as well as fermentation pattern and net ammonia nitrogen (NH₃-N) accumulation), together with crude protein (CP) content. For a feed to show potential as a pasture replacer, ARDOM was expected to be at least comparable to that of the pasture, while preferably supplying some extra CP. The potential of these feeds as complementary supplements was evaluated based on the net NH₃-N accumulation and branched-chain fatty acid (BCFA), along with CP contents as an indicator of RDP supply and in vitro propionate production as a proxy for glucogenic nutrients (GN) supply. Enset (Ensete ventricosum) leaves and water hyacinth (Pontederia crassipes) leaves exhibited a moderate reduction in fermentability, with approximately 15.5% lower total VFA and ARDOM than pasture (p < 0.001), however they showed higher net NH₃-N accumulation (19.4% and 43.8%, respectively) along with higher CP (141 and 157 g kg^-1 DM, respectively) than average pasture (110 g kg^-1 DM), indicating their potential as alternative feeds. Conversely, Euclea divinorum leaves showed a marked reduction in fermentability, with approximately 50% lower total VFA and ARDOM than pasture (p < 0.05), lower or negative net NH₃-N and lower CP (85 g kg^-1 DM) than average pasture, which made it less suitable as pasture alternative. Generally, mango seed kernels showed poor in vitro rumen fermentation characteristics compared with pasture. By contrast, Moringa stenopetala and Moringa oleifera pods demonstrated an interesting potential as complementary feeds to pasture because of high net NH₃-N, BCFA, CP, and propionate (p < 0.001). They also exhibited higher or comparable ARDOM relative to pasture. Enset corms showed higher total VFA and propionate than pasture (p < 0.001), yet with negative net NH₃-N accumulation (p < 0.001). Utilizing enset leaves and water hyacinth as alternative roughages could mitigate feed shortages and reduce grazing pressure in tropical regions, whereas Moringa pods and enset corms as complementary feeds could also enhance the efficient use of tropical low-quality forages in dairy cows.