Georgian era (looks like newly brass plated over white metal)
I have seen one exactly like this sell at auction for $1300 in 2004. It was described as a Slave Collar despite clearly having 'whose dog are you' engraved upon the name plate. Would look beautiful as a piece of jewellery. The man I bought it from adorned his Saluki with it.

Brass Plate Antique Dog Collar

£600.00Price