
In my breed I think most people prefer to avoid having pups during the busiest part of the show season during the summer. We do seem to have more pups registered in the first and last quarter than the two middle ones.
Of course the bitches don't always co-operate, but I like to have pup November to March, with December to February for preference.
For me some of this is also to do with less likelihood of neighbour issues over puppies getting vocal, as the daylight hours are shorter. Also with my breed I have had no problems keeping them warm, but have found hot weather very stressful making Mums and pups upset and also disrupting sleeping and eating patterns.