Only once?
Incidentally, I believe Pandas are pretty much The Most Pathetically Inept Creature Ever. Their physiology and diet are so horribly mismatched that they struggle to reproduce at the best of times. The milk they produce is so low in fat (due to their poor diet) that their young are always on the edge of starvation. This exacerbated by the problem that they give birth very early, because their diet is so poor that they can’t afford the energy to carry the foetus until it is properly developed.
This may all have been misinformation by Mr Attenborough, but I think you should be shooting for something a little more successful than a Panda.