Dogs are colourblind and struggle to distinguish between red and green, meaning finding a red ball in the park could prove tricky, scientists have said.

Experts have known for some time that dogs have poor vision, and are up to eight times worse than humans at seeing things in detail. But until now, nobody knew why.

Now scientists have developed a test for dogs and found that they struggle to tell red and green apart, much like colour blind humans, a condition known as deuteranopia.

In the wild, dogs are a crepuscular species, meaning they are most active in dawn or dusk, for which colour vision is not needed. But through domestication, pets are awake mostly in the daytime, for which their eyes have not yet evolved.

Dr Marcello Siniscalchi, of the department of veterinary medicine at the Univesity of Bari in Italy, said dog trainers may want to avoid red clothing or shoes if working on grass, because animals will struggle to see their movements.

“Overall, the direct demonstration that dogs are red-green colour blind is not only important for people directly involved in dog training but also for owners who want to improve their dog's attentive skills during some activities such as play that is at the heart of a healthy owner-dog relationship,” he added.