Witchcraft in this world is practiced openly by witches and is exclusively female. Magic works through long, complicated rituals that require multiple components. The most powerful of these demand human sacrifice, in which an individual is killed and their mana (life energy) is used to fuel a spell. Mana is continuously produced by the body in order to keep a person alive and functional. It exists in various quantities in different places, such as the heart, blood, intestines, liver, etc. Certain rituals require certain parts to be used (burned, eaten, etc) in order to release the mana that resides there and fuel a spell. Some examples would be cutting out the heart of a person and devouring it in order to add their mana to yours and temporarily increase your strength before going to war, or hundreds of people would be burned in a pit to fuel a battalion of soldiers. Sacrificial victims could be criminals, prisoners of war, and other undesirables that society deem fit to be killed. This would depend on the state and their laws and customs.
Witches who are sentenced to die for whatever reason are routinely just killed with no special circumstances. Again, depending on the policy, this could be brutal or humane. Males, however, are regarded as better components for these kind of spells. Why would this be the case?