sentences:  Of concern is the health risk associated with the use of medicinal herbs that contain PAs, notably borage leaf, comfrey and coltsfoot in the West, and some Chinese medicinal herbs.Some ruminant animals, for example cattle, showed no change in liver enzyme activities or any clinical signs of poisoning when fed plants containing pyrrolizidine alkaloids.Yet Australian studies have demonstrated toxicity Sheep, goats and cattle are much more resistant and tolerate much higher PA dosages, thought to be due to thorough detoxification via PA-destroying rumen microbes.