Misuse mate .Dehydration and stress .Perhaps ive seen some bad examples but id rather a good summer litter than nurture a touch and go autumn,winter litter that needed heat and before anyone says it ,dogs do not need heat lamps in the summer in any shape or form to rear a litter .Each to their own i guess ,just my take .It also means someone has to be checking them a lot more than without due to the thing failing etc ,hence more fuss ,more stress .Like i said just my way and i wont be changing any time soon .