This new two-part series follows tiny Chihuahuas, working Sheep Dogs, rescue pups in need of a home and amazing assistance puppies that will one day transform the lives of disabled people.

Viewers will have a privileged look at the rarely-seen magic of the early days, through to the moment they move to new homes, and see how puppies form the strongest bond of their lives: not with their mums or their siblings, but with humans. In Devon we meet Snuggles, Smiley and Cheeky the Chihuahuas at just a few hours old. They can't see or hear properly, but they can smell and sense heat, guiding them to what they need most: mum's early milk, which is packed with energy and antibodies to protect the vulnerable newborns from disease. Chihuahuas are offi-cially the world's smallest dogs, so puppies don't come much tinier than this. Amazingly they only weigh around 100 grams, lighter than an apple and far, far sweeter.

The Chihuahua puppies are being reared by hobby breeder Dan, who says: 'When you first hold that little puppy, it's just incredible… I think I'm quite hard-faced about certain things, but it gets me welling up every single time.'

In the Cotswolds are two boy and four girl Labrador Golden Retriever

cross puppies who have a special destiny ahead of them as assistance dogs for the charity Dogs for Good. In Gloucestershire are eight Border Collie pups, five girls and three boys while in Essex the fourth litter of five puppies are in desperate need of a home – they're living at Dogs Trust, the UK's largest dog welfare charity, who care for almost 17,000 dogs every year.

Over the following weeks cameras will follow the four litters as they reach various landmarks and see how puppies can sleep for as much as 20 hours a day due to the tiring of their untrained muscles and how a staggering 80 per cent of puppy play involves biting.

After eight weeks, the puppies take the next step on their journey, having laid the foundations for the special bond that will define their lives with their new human families.

Puppy Secrets: The First Six Months is on ITV at 8pm tonight