<P> When intravenous injection is not possible, euthanasia drugs such as pentobarbital can be injected directly into a heart chamber or body cavity . </P> <P> While intraperitoneal injection is fully acceptable (although it may take up to 15 minutes to take effect in dogs and cats), an intracardiac (IC) injection may only be performed on an unconscious or deeply sedated animal . Performing IC injections on a fully conscious animal in places with humane laws for animal handling is often a criminal offense . </P> <P> This can be an appropriate means of euthanasia for large animals (e.g., horses, cattle, deer) if performed properly . This may be performed by means of: </P> <Dl> <Dt> Free bullet </Dt> <Dd> Traditionally used for shooting horses . The horse is shot in the forehead with the bullet directed down the spine through the medulla oblongata, resulting in instant death . The risks are minimal if carried out by skilled personnel in a suitable location . </Dd> <Dt> Captive bolt </Dt> <Dd> Commonly used for cattle and other livestock . The bolt is fired through the forehead causing massive disruption of the cerebral cortex . In cattle, this stuns the animal, though if left for a prolonged period it will die from cerebral oedema . Death should therefore be rapidly brought about by pithing or exsanguination . Horses are killed outright by the captive bolt, making pithing and exsanguination unnecessary . </Dd> </Dl>

What drug do they give dogs to put them down