The sensitive socialisation period in puppies (3-14 weeks) is the most important developmental window for welfare, with experiences during this period having lifetime effects on behaviour and fear.
The socialisation period is the most leverage point in a dog's lifetime welfare trajectory. Adequate positive exposure during this window creates confident, resilient adult dogs. Deprivation - whether through isolation, puppy farm early separation, or lack of owner knowledge - creates fear-based behaviour problems that cause chronic suffering and are difficult to fully remediate. Breeders and new owners bear shared responsibility for optimal socialisation.