英语语法分析

If the grazing rearing was still used, the medicaments deworming must be utilized to drive trematoda in the ducks within 20-30 days from starting their grazing rearing.

如果仍然采用放牧的模式饲养，则放牧鸭群从开始放牧后20—30天内应做好吸虫的药物驱虫。