Weeds are unwanted plants that grow along with crop plants. During the harvest time of crop plants, some weed plants are also harvested and seeds of weeds may cause some harm to livestock because these weeds are poisonous in nature. Some poisonous weeds are like grasses. During the collection of food for livestock, they come along and harm the animals. They release toxins and are harmful during consumption. Both people and cattle are poisoned by water hemlock plants.