Here are some alternative textures for you to use, simply rename the texture you want so that it no longer has a number. So for example, delete the original cow.png and rename cow2.png to cow.png.

If you would like a random texture to display in game for every mob, please install: https://github.com/FarnGitHub/Farn-s-Random-Mob/releases/tag/1.3.1 by adding the zip file to the "Version" tab of a b1.7.3 instance within MultiMC (or any fork/alternative of MultiMC.)