At least for these animals the game has already some models. I do not know anything about its quality and I agree that in future there should be more animals within the game. But when I look at these models I am pretty sure that we could expect some in the future.
To be honst from my point of view it is not a good idea to implement pigs or cows if you do not have the game mechanics implemented to get milk and sell milk ( a specific trailer) and a place to sell it and so on.
Some for chicken and eggs. If we do not have the trailers and economy and so on we do not really "need" these additonal animals at the moment.
So from my point of view we do not only need more animals but we need all the other things around a specific kind of animal.
if I am not deceived, they are the ones that come with the engine version when you buy it there for many years are to do tests and learn since in the demo version that I downloaded they were already
I once put all the animals that are included in the game code on the test map. these are in the pasture on the courtyard.
If you are interested, you can take a look at it.