
It is any 12 month period! So say your first and fifth litters were born 11months and 29 says apart you would be required to be licensed, even if the next year yopu didn't breed at all.
As already said these rules arepart of the Breeding and sale of dogs (welfare) Act. The law for registered breeders imposes various other requirements such as minimum period between litters, and a minimum age of sale of 8 weeks, proper record keeping etc.