VETS are asking East Lancashire dog owners to keep their animals on leads when walking near sheep.
It comes as the annual lambing season gets underway.
British Veterinary Association president and vet Robin Hargreaves said ewes were particularly vulnerable at this time of year and sheep worrying could have tragic consequences.
He said: “Even dogs who are usually calm and good natured can become very excitable and difficult to control when faced with livestock.
“Tragically this can lead to chasing, attacks and fatalities for sheep and other animals.
“Over the coming months ewes in the field are likely to be heavily pregnant or to have recently given birth.
“Chasing and worrying can have severe consequences at this time, leading to serious injuries, early labour and fatalities.”