@iliekponiez This is just a shot in the dark, but does one of your sims have a Collection Helper, and do you leave it active? If so, try turning it off.
Other than that, are you up for a little testing? If so, it might be worth purging all the wild animals in Appaloosa Plains to see whether it helps. I have no idea if it will, but that's one obvious difference between AP and Oasis Landing. If you're interested and are willing to use a few mods, please install NRaas ErrorTrap, Overwatch, MasterController, and Register, if you haven't already.
When you load AP, click on City Hall or an in-game computer and select NRaas > Register > Animal Control, and set the number of each type of animal to zero. Then, if you don't want to wait for the existing ones to be removed, you can do so manually: NRaas > MC > Sim > Advanced > Total Annihilation > Species > [all but human]. Select only the strays and wild animals from the list, not the resident pets at first.
As a side note, there will always be some extra animals listed that never appear on-camera: cats and dogs from the adoption service, horses available for breeding. You can delete these too, but they'll just respawn. However, they won't affect performance, so don't worry about them either way. I'm mentioning them so you don't think you need to keep purging them or that the process didn't work properly.
Once you've done this, use "save as" to rename the save, so the original remains intact as a backup, quit, delete the cache files in your user folder, and reload. For reference, the cache files are:
- CASPartCache.package
- compositorCache.package
- scriptCache.package
- simCompositorCache.package
- socialCache.package
If this helps, but you don't want to lose all the strays, you can try with one or two categories at a time, e.g. removing the horses and unicorns and deer but leaving the others. If it doesn't help, try removing the domestic horses too. That would be sad, or at least I'd be sad, but it's worth finding out either way.