No, they're euthanized. Big difference in the humane department.
In theory, this statement is true. But in practice it is not always, or even usually the case. For example, one of the most common forms of mass euthanasia is the CO2 chamber. The way this is supposed to work is the animals are placed in the chamber that has natural air and slowly the CO2 levels are increased until the animal falls asleep and dies peacefully. In reality, the people working these chambers often become immune to the deaths of the animals on some level and they want to "get the job done." They will "charge" the chamber with high, sometimes lethal levels of CO2 before putting the animals in. The animals are then aware that they are suffocating and panic through the process. I have this information directly from someone who had to do community service volunteering at a local pound.
I apologize for what may seem graphic to some, but I did leave out the gruesome details including only enough to make my point.