I have some pig textures that won't work except for the biome specific ones, the baby, and the nametaged ones. To be clear, the "skins.1" doesn't work, they show up as just regular pigs.
From the Optifine docs:
# (Required) Range of entity textures to use.
# The texture index "1" is the default texture from "assets/minecraft/texture".
textures.<n>=<list of texture indices>
# Alternatively the Random Mobs property "skins.<n>" can be used.
# skins.<n>=<list of skins>
Make special note of that second point. Index "1" is a little different. If you currently have a variant assigned to that texture, you'll need to move it to a different index number in order for it to work.
I am aware that index "1" is the default texture, but I don't know how that knowledge will help me solve my problem. Previously when I said "skins.1" is the one not working, I meant that "skins.1=2-5 7 9 12 14 15 19-29 31-40 42 44" isn't working from the properties file I posted.
I tried changing "skins.1" to "skins.2" (and then re-numbering all of the others) and then gave it a list of forest and plains biomes, but that didn't work. I have a feeling that optifine doesn't like the baby specification and doesn't act properly when using it but I haven't tested it.