Farmers are being urged to vaccinate livestock against bluetongue as midge activity reaches its peak period.
The risk of the disease spreading is increasing every day as the country enters the height of summer, the NFU said.
Livestock owners should remain vigilant for the disease and inspect animals on a regular basis, particularly the mucous linings of the mouth and nose, it added.
“We are concerned that there has been a drop in the number of suspect cases being reported compared to this time last year.
“It is imperative that livestock keepers monitor their stock closely and are aware of the symptoms of bluetongue.
“If there’s any doubt at all farmers should inform their local animal health office or call the DEFRA helpline.”
The NFU said clinical signs varied, but in sheep symptoms included eye and nasal discharge, swelling of the mouth, head and neck, respiratory problems and lameness.
Cattle sometimes showed no signs of the illness, but symptoms included conjunctivitis, swollen teats, tiredness and saliva drooling from the mouth.
“If livestock keepers aren’t sure about the symptoms they can get advice from the local animal health office, local vet or the DEFRA website,” the union said.
“It is essential that any suspect cases are reported and livestock keepers should remember that the vaccine is still available and can be ordered from their local vet.
“It’s vital we protect our industry from this disease, so the message remains very clear – don’t hesitate, vaccinate.”