A farmer in Holme Moss, West Yorkshire, was left heartbroken after 28 sheep were discovered dead in a field on Wednesday.
Several of the carcasses showed bite marks, while a few were recovered from water close to the farm.
Photos released show the bodies stacked inside a trailer following the grim find.
Laura-Jane, who owns the flock, posted on Facebook that she felt "absolutely devastated" by the loss.
She noted the sheep had been "alive and appeared perfectly healthy" just a day earlier.
Laura-Jane suggested the animals might have been "grabbed" by another creature, hinting at a possible chase or attack by dogs.
A post-mortem examination was performed, yet veterinarians could not determine a definitive cause of death.
Three additional sheep are reported to be seriously ill.
In her statement, Laura-Jane said: "Absolutely devastated to have found 28 of our sheep dead in a field near Holme Moss. All were alive and appeared perfectly healthy yesterday.
"Some were found dead in the water, while others had visible bite marks and clear signs of having been grabbed by another animal, raising serious concerns that they may have been chased and attacked by a dog or dogs.
"Post-mortem examinations have been carried out, but the vets have found no obvious illness or underlying health problems to explain the sudden deaths.
"We also have another 3 sheep at home that are extremely poorly."
She has urgently appealed for any leads, urging anyone who saw loose dogs, chased sheep, or anything unusual in the Holme Moss area to contact her.
"To lose 28 healthy sheep in such a short space of time is absolutely heartbreaking. We desperately need answers. Please share any information, however small, could help."
