Secondary plant metabolites from the leaves of trees and shrubs, such as tannins and saponins, can potentially alter the microbial environment in the rumen of the dairy cattle and thereby reduce enteric methane formation. Results from the literature on the use of leaf hay additives in feeds as a methane mitigation option are varied and dependent on types and doses of metabolites. Experimental work is done on the leaves of Fraxinus excelsior, Hedera helix, Salix viminalis, Leucaena leucocephala as additives to maize silage. Results from in vitro trials showed that all species reduced methane formation, but also the degradability, when used as pure feeds compared to maize silage. When applied as 3% additives to maize silage no significant effects on methane or degradability was observed. H. helix reduced degradability significantly less than other leaf hay species as pure feed, rendering it an interesting species to do further research on. Agroforestry systems with trees and shrubs on pastures are practised in some cultures and grazing of forestlands has been more common in Europe historically. These systems are again receiving attention for their multiple environmental benefits, such as biodiversity enhancement, soil protection, and carbon sequestration. Leaf hays potential to reduce enteric methane should be considered in the design of modern agroforestry systems with grazing ruminants.
Niels Mark Jacobsen