Grazing of pasture weeds by goats and sheep. 2. Scotch broom (Cytisus scoparius L.)

Abstract

Sheep and goats were allocated to 1.6 ha paddocks containing populations of scotch broom with 4–10% ground cover and grazed by either 4 sheep or 6 goats. Subjective scoring of defoliation and persistence was conducted at 4–8-weekly intervals over almost 2 years. While the sheep had minimal impact on the vigour of the broom plants, goats had a major impact when broom density was low (4% ground cover) but no impact when broom density was at 10% ground cover. This same pattern was evident for defoliation. Goats also stripped bark from broom stems during winter increasing broom ill thrift in goat paddocks. While sheep browsed up to 90 cm height, goats browsed up to 120 cm at low broom density. Both sheep and goats removed stem and flowering points preventing seed production within browse reach and also removed the new broom shoots over summer, whereas sheep preferred pasture once it became more abundant. Pasture availability was greater in goat-grazed paddocks over the flowering period and when new shoots were produced by broom. When broom seeds were fed to goats, 8% of the seeds remained viable following ingestion.