NUTRITIVE VALUE AND IN VITRO DIGESTIBILITY OF NON-CONE HOP (HUMULUS LUPULUS L.) BIOMASS

Abstract

More than 50% of hop ( Humulus lupulus L.) biomass is discarded as waste. Potentially, this by-product, comprising leaves, bines, and unrecovered cones (non-cone biomass) can be processed into a high value forage. In this study we used classical forage and hop analysis methods to determine the nutritive and chemical properties of non-cone biomass from five (Cascade, Chinook, Newport, Nugget and Zeus) hop cultivars. Cascade had significantly higher crude protein ( p ≤0.05), while ash, starch and sugar content were not statistically different among cultivars. Acid and neutral detergent fiber ranged between 187-295 g·kg -1 and 274-397 g·kg -1 of DM, respectively, with Cascade recording significantly ( p ≤0.05) higher fiber than other cultivars. In vitro, dry matter (604-685 g·kg -1 ) and NDF (374-478 g·kg -1 ) digestibility were significantly ( p ≤0.05) higher in Newport, while true dry matter disappearance (709-793 g·kg -1 ) was significantly ( p ≤0.05) lower in Cascade. Variations were also observed in plant metal content with Ca being significantly ( p ≤0.05) lower in Cascade, K in Nugget, and S in Zeus, while Mg was highest in Newport. Overall, crude protein and nonstructural carbohydrate content in hop biomass were comparable, respectively, to alfalfa, and to forage grasses like brome and Kentucky bluegrass, and acid and neutral detergent fiber levels were slightly lower than in alfalfa and legume-grass hays. Digestibility also compared favorably to other forages including legume-grass hays and alfalfa silage. Hop biomass can be a good source of dietary calcium, magnesium, and trace elements, and furthermore was found to contain low levels of lupulone, a compound in cone biomass recommended as a natural alternative to synthetic antibiotics. Our findings suggest non-cone hop biomass may be of significant value as a supplement in livestock nutrition.