Dogs were popular in Ireland and they roamed free. Complaints about them were frequent – they attacked and even killed the livestock and people lived in fear of being bitten by a rabid dog. No one knew who the owners of the dogs were so, in 1865, Parliament passed a law requiring the Irish to register their dogs –
By March 31st of every year the owners had to go to the local petty sessions court to register their dogs. For the Aherns that would have been in Oldcastle. In 1866, the first year of the law, John Ahern went to Oldcastle in February to register his black mastiff. Within a few years, most people were waiting until March to register the dogs. The real rush came the last few days with several hundred people lining up to make the deadline.
If you didn’t register the dog you were subject to fines.
The copy of the “Bill for regulating Keeping of Dogs and for Protection of Sheep and other Property from Dogs in Ireland” comes from http://eppi.dippam.ac.uk/documents/14740; Sessional Papers 569, Volume 1, Session 1865