Forage shrubs in North Island hill country 3. Forage digestibility

A range of shrubs was evaluated as potential sources of forage for grazing animals. Shrubs were established in rows in hill pastures near Wood ville. Nine “true” shrubs, and two erect grasses, pampas grass ( Cortaderia selloana ), and toetoe ( C. fulvida ) were evaluated. The true shrubs were: Chamaecytisus palmensis , tagasaste; Medicago arborea , tree medic; Ulex europaeus , gorse (two variants: wild gorse and short‐spined gorse); Cytisus scoparius , broom; Robinia pseudoacacia , black locust; Leptospermum scoparium , manuka; Cassinia leptophylla , tauhinu; and Ceanothus griseus , ceanothus. Digestibility of shrubs was assessed by in situ (nylon bag) digestion in cows' rumens, and by in vitro (cellulase) methods. The two methods ranked most forages similarly, but some inconsistencies did occur. Tree medic and tagasaste were highly digestible (71–73% estimated in vivo DM digestibility). Manuka, pampas, and toetoe had low digestibility (48–56%). Stem material was less digestible than leaf. Digestibility was strongly related to combinations of functions of cell wall content, degree of lignification, and degree of silicification. Oesophageal‐fistulated sheep and goats were allowed to graze each of the shrub species in the field. They selected a diet 5–6% units more digestible than the average of the forage on offer.