Pertinax, this is what I meant - if female elephants are put together with a mature bull when they`re young (10-20 years old), they will usually get pregnant by natural mating and deliver without problems, and there is nothing AI can do better then natural mating.
And taking Whipsnade as example, I`d say even AI can`t do much if the females have already passed the ideal breeding age - out of 6 females, 2 never got pregnant at all (Mya and Dilberta - do I understand you right Vetandy that AI might have tried on both?), 2 fell pregnant but had very serious birth complications that resulted in the death of both calves and one female, and only 2 delivered healthy calves (and 50% of those died from herpes). That is not exactly a good result, espcially if you compare this with the natural breeding results in Emmen, where 6 of 6 young females bred and until today raised a grand total of 17 surviving calves until today (+ 2 born to Emmen females in Cologne).
Regarding the problems Whipsnade is facing now, I am not sure that stopping all breeding attemps is necessary now. In my opinion, they should change to protected contact and keep the calves as stress-free as possible..
If you look at other zoos that lost calves to herpes, they usually have continued breeding with a good survival rate (for example Rotterdam lost 2 calves to herpes in 1998 and 2002, but 9 other calves born to females from the Rotterdam herd in Rotterdam and Dublin from 1997 - 2009 are surviving until today).
The former Port Lympne elephants have not been retired from breeding neither, Bindu is the breeding bull in Cologne, and the only 2 females in breeding age are now at Antwerp where Khaing Phyo Phyo is due to give birth again any moment.
By the way, I am not sure that the 2 stillborn calves in Port Lympne in 2005 both died due to herpes, I have heard that the calf of Tin Tin Too died because the mother had many benign tumors in the uterus. She was considered to be infertile due to this condition and everyone was surprised when she showed signs of labor, but she could not expell the calf due to the large tumors and both died. This is at least what a friend of mine had been told by a keeper in P.L.