Police are appealing for the owners of more than 20 horses found in Alfreton to come forward.
The 22 horses were discovered on land off Park Mill Drive to West Houses, between Alfreton and South Normanton, on Monday.
The Control of Horses Act 2015 clamps down on people illegally abandoning the animals – a practice known as fly-grazing – in a bid to improve horse welfare and standards.
Fly-grazing horses can be designated to another landowner after only four days under the act, which came into force earlier this year.
Police want horse owners to check their stock before the cut-off date for the animals to be moved on Friday.
Community Safety Inspector Erika Green said: “Although this is not directly a policing issue, we are working closely with the landowner and the county’s Horsewatch co-ordinator Leslie Manger to try to locate the owners of the horses.
“Some of the animals are microchipped but they are not registered so I am urging local horse owners to ensure they are not missing any animals.”
Anyone who has information or would like any more details should call police on 101.