You have to be careful with horse and cow poo. Some of the worm-killer drenches given to horses, cows and sheep are designed to last for a long time, and of course they are for killing worms. It isn't true that the are inactive once they come out of the animals. A study done here to look at the effect of horse poo in national parks showed that the inhabitants of leaf litter and soil were killed by it. The areas around the poo remained empty of invertibrates for at least several months. Joy