ZOO keepers in Edinburgh have started daily tests to try to work out the best time to mate their giant pandas.

Edinburgh Zoo is collecting samples from female panda Tian Tian to pinpoint when she will be most susceptible to male panda Yang Guang's advances.

She is expected to be in season at some point between the start of March and early May and the tests will help the zoo pinpoint when to introduce the pair for breeding.

Panda keeper Alison Maclean collects one sample from Tian Tian every morning and each afternoon one of the zoo's veterinary team takes a further sample from the panda.

These samples are then taken to Chester Zoo in England for hormone testing.

The tests are similar to the urine tests done on humans, with the experts looking for a rise in the concentration of oestrogen.

Female pandas are only interested in mating for three days a year but it is hoped Tian Tian and Yang Guang will produce a cub during their spell in Scotland.

Iain Valentine, director of research and conservation at Edinburgh Zoo, said: "The scientific work behind the scenes has very much begun. It is vital for us to have as full a picture as possible of when Tian Tian is receptive to mating, as the window will only be three days.

"Although not with each other, both pandas have bred before and we are fairly optimistic we can achieve a successful breeding. Signs have been positive to date and Tian Tian has had time to get used to the scents and sounds of Yang Guang.

"Primarily dictated by light levels, which are different here to the part of China the pandas are from, we do not know exactly when Tian Tian will be in season. However, we expect it to be between the start of March and anytime up to very early May."

Dr Sue Walker, endocrinologist at Chester Zoo, said: "This rise in oestrogen will coincide with breeding behaviour in the panda and allow keeping staff to determine the most appropriate time to introduce them for breeding."