Officers say a ewe and her lamb were bitten by a loose dog during the incident on a farm near Calow on Tuesday, April 12.
A spokesperson for Derbyshire Rural Crime Team said: “Another day, yet another loose dog attacking sheep, this time on a farm close to Calow, Chesterfield.
"The flock was chased and a ewe and her lamb bitten.
"Not only does this cause untold stress to the sheep during the lambing season, it causes the famer unnecessary work, stress and expense.
"You MUST keep your dog under control at all times and once the attacking dog is identified, you will be getting a visit from the police.
"If you have any information about this attack which occurred Tuesday, April 12, around midday, please call 101 and quote incident 545-12/11/2022.”