Horses are not native to Australia. Over the centuries domesticated horses have run wild across the land. The wild "breed" of horses are called Brumbies. Like the introduced camels they reach pest proportions.
Environmentalists usually kick up a fuss when it is decided to carry out a cull. However, this is necessary as they do not have natural predators here. Horses, donkeys and camels are dying of starvation as the land will not support the numbers. It is more humane to shoot them.
farmers establish water points for cattle and sheep. The wild animals hang around water holes and eventually destroy them. Consequently, native species are dying from lack of water.
Culling is being done from helicopters. The shooters are very accurate and there is no suffering. Unfortunately, it is necessary to leave the animals where they die because it is too expensive to take them to an abattoir to use as pet food. It is a pity really. Ancestors of the horses were used by the Australian Light Horse in WWI.