Edible forage yield and nutritive value of poplar and willow

Abstract

Poplar and willow on farms are a potential source of supplementary forage during summer. To incorporate poplar and willow into farm feed budgets, a method is needed to non-destructively estimate the edible forage yield of the trees. Also needed is an estimate of the nutritive value of the forage. Previously uncut trees on hill farms in the lower North Island were measured and a relationship between tree forage yield and diameter of the trunk at breast height (DBH, 1.4 m) was developed. The DBH was from 5 to 32 cm and the forage yield from 1 to 66 kg dry matter (DM)/tree. Nutritive value of poplar and willow (metabolisable energy 8-9 MJ/kg DM) was similar to that of normal summer pasture, but was lower in fibre and higher in soluble carbohydrate, and of higher nutritive value than drought pasture. The concentrations of the secondary chemicals condensed tannins and phenolic glycosides were high in poplars and willows, and they have some positive effects on livestock performance, but their role requires further research. It was concluded that poplar and willow provide forage of sufficient quantity and quality to warrant using them as supplements to pasture for feeding to livestock during summer droughts.