Whereas I do understand the rationale for AZA and its target species conservation breeding programs, I am no supporter of any phase out where almost over night the species of which individuals are still living in captivity become worthless and are (then) neglected to the point their biological needs (of which reproduction is one) are ignored forthwith.
Why in these instances does the policy phase out fail where individual of any such species on target phase out are then not transferred to other regional zoo associations where the species would be of benefit as well as a possible desired target species. You are effectively condemning these to functional extinction (which happens in nature only when only individuals of one sex remain and no options are available in the wilds to find mates of the opposite sex and fulfilling the biological life path to reproduce and care for the next generation(s).
While I will absolutely not deny that many phase-outs and general handling of populations within AZA facilities have not always historically been handled in best practice. Some major, shameful mistakes have been made and many facilities and programs are still dealing with those consequences. That said, I think that it is a rather harsh and unfair blanket statement to say that the animals in a phase-out population are considered worthless overnight or that they are suddenly forgotten about or neglected-- I think you would find that that statement would not fall well on the ears of any staff member caring for any of these animals. I can assure you that those animals are still receiving the same level of care as any other animals in the collection, even if they are no longer "valuable" to the collection's future. Many of the animals that find themselves in these situations are older individuals that are past breeding age anyways (whether or not they were kept out of breeding situations historically is another question, but unfortunately, what is done, is done--- see mismanagement referenced above). If the animals are still of breeding age, most facilities will try to place them in breeding situations outside of the AZA. For example, a large number of ungulates that have and are being phased out of the AZA are sent out to breeding situations in the private sector. Lowland tapir are rather common and are breeding in the private sector. The very few left in the AZA, with the exception of Brookfield's pair, are all well advanced in age.The facility at which I work is currently home to a small herd of common eland, that while they are not a phase-out species in the AZA, they are a phase-out species at our facility. These animals, including two elderly individuals, are still receiving the same level of care as the rest of our animals, even though we are not breeding them any longer and are looking to phase-out the species. We are still as vigilant with their health and well-being as we are with our "extremely valuable" animals. We have been slowly but surely placing our breeding age animals at other facilities where they will be able to continue breeding-- eland just aren't the easiest animals to place, so it has been a few at a time.