Those Czech zoos that euthanise surplus offspring (not all do it) are usualy pretty open about it. They get backlash but it is smaller than if they euthanised animals in secret and then it would be "revealed" to unsuspecting public by a journalist. On the other hand, old animals are not euthanised (unless it is heath related), even lonely old animal will be given best care for years, because it is seen it has earned it by many years "serving" for the zoo. So euthanising for example of last lion or monkey after death of its companion, which is surprisingly common in Australia etc., would not fly here.
We have sad historic examples of captive breeding programs that have collapsed and ceased to exist just because at some moment holding capacity was full or that species was not "in" for time beeig, all zoos simultanously stopped bredding for some years. And when capacity was freed partly again, zoos realised all females grew old or their anticonception could not be reversed anymore, and all the hard work of several generations of zoo workers was just for naught. All those animals who were catched in nature, that were founders of the breeding program, were caught for nothing, their genes didnt survive in the end, only due to bad management.
Zoos in the past were more like museums, they would buy animals, exhibit them, took care about every single animal till its death (so they didnt need to buy a new one). Ever since zoos have decided to stop bringing in new wild-caught animals and started managed breeding programs, they have changed from "museums" into "farms". With all related ethical problems.
Each person drows its limit what animal is ok to be slaughtered. Nobody oposes vermin control like poisoning of rats in sewer system. Vegans dont want any domesticated animal to be killed. "Average" person is ok with slaughter of domestic animals, vernison (deer, wild boar etc.), but doesnt want most large popular zoo animals to be killed. They would be ok with antelope/bison/fox, probably not with a monkey or dolphin. What we see as acceptable is based on cultural norms and individual ethics so it will differ between countries. I urge people to always keep in mind we dont have universal norms on this planet. They change rather quickly depending on space and time.
We have sad historic examples of captive breeding programs that have collapsed and ceased to exist just because at some moment holding capacity was full or that species was not "in" for time beeig, all zoos simultanously stopped bredding for some years. And when capacity was freed partly again, zoos realised all females grew old or their anticonception could not be reversed anymore, and all the hard work of several generations of zoo workers was just for naught. All those animals who were catched in nature, that were founders of the breeding program, were caught for nothing, their genes didnt survive in the end, only due to bad management.
Zoos in the past were more like museums, they would buy animals, exhibit them, took care about every single animal till its death (so they didnt need to buy a new one). Ever since zoos have decided to stop bringing in new wild-caught animals and started managed breeding programs, they have changed from "museums" into "farms". With all related ethical problems.
Each person drows its limit what animal is ok to be slaughtered. Nobody oposes vermin control like poisoning of rats in sewer system. Vegans dont want any domesticated animal to be killed. "Average" person is ok with slaughter of domestic animals, vernison (deer, wild boar etc.), but doesnt want most large popular zoo animals to be killed. They would be ok with antelope/bison/fox, probably not with a monkey or dolphin. What we see as acceptable is based on cultural norms and individual ethics so it will differ between countries. I urge people to always keep in mind we dont have universal norms on this planet. They change rather quickly depending on space and time.