The impact of cutting prior to goat grazing on variegated thistle (Silybum marianum)

Variegated thistle (Silybum marianum) is a prevalent weed on the East Coast of the North Island of New Zealand. Goats may provide a novel management tool to control thistles, but little is known about how cutting thistles prior to grazing affects thistle consumption by goats. This study investigated the extent to which goats consume either uncut entire variegated thistle plants or cut thistles. Eight groups of three goats were presented with thistle vegetation in each of two replicate 1-hour feeding sessions on 2 consecutive days. Averaged over both days, in the cut treatment, goats consumed 99% of the leaves that had been removed from the thistles and reduced the ground cover of the thistle plants by 68%. In the uncut treatment, ground cover of the thistles was reduced by 46%. A combination of cutting and goat grazing is likely to be a useful tool for stopping variegated thistle debris from smothering pasture and for inhibiting seed setting. Further work is required to test this at paddock scale.