We got Motorcycles. We got Trucks. We got APC's. But what about using good old animals for war?
Both imported horses and tamed local creatures could work. Of course if realism is wanted, several things have to be considered.
Size is rarely considered nowadays, but to be actually effectively rideable into combat the horse needs to be large enough. The size of modern breeds ranges from barely 1000s to over 2000s.
During the bronce age, few horses were large enough for riders. So the chariot was the closest equivalent to cavalry in the day. Note that the size can go very small - Dogs can also drag a sled/chariot.
So I guess small animals can only be used for Chariots - wich are basically trucks.
Not trying to ride a Lion is obvious. But did you know that most Herbivores are quite agressive as well?
It must be clearly said that Zebras are not just stripy horses!
If you capture the dominant horse of a group, the rest will follow. And it will not fight you too much.
A Zebra herd could not care less for one of them being captured. You got to capture them one after the other. And good luck rearing up new generations. That is if you could keep capture one in the first place. They will basicalyl fight you until either it is free or it is dead.
And let us not get started on Hyppos, wich hold the murder record for Animals in africa. Yes, they are more dangerous then the actuall carnivores. By an order of magnitude.
I guess they should not have a too high c-rating.
Of course very agressive animals can be used as well - as the fighting part of the force. Dogs have been and are still used as attack animals. Small Frame, social structures, natural weaponry, predator instincts.
Just make sure you properly train your anti-tank dogs.
The ideal tamed and domesticated animal eats something that humans do not eat.
However even if they do not, this would be less of a problem in Shadow Empires: The powers do have industrial era food production and supply mechanics. And a severe shortage of manpower and IP. So even if the Animals ate the normal food, that can still be prefereable over machines that eat fuel!
Why use Biofuel Refinery when you got a food/work converter already there?
On this front, high Xeno Toxicity could actually help. Imported animals would need to be supplied the hard way, but tamed local ones would have food sources humans definetly can not use!
Equipment and IP
Atmosphere Hazard for humans, is also Atmosphere hazard for all domesticated Earth Animals.
If it is just air filters/oxygen enrichment gear or radiation filters, animals could be fitted with that as well. It woud adds some material cost. Animals in war have regulary been armored, so that is not a big extra cost.
However at some point the investment in protecting the animal will outweight the advantage of having them in the first place. Latest when you would need Thermal- or Environmental suits, it would loose all benefits. You propably spend more IP on cladding them in a custom spacesuit then it would cost you to just get a bike instead. And especially the war dog, looses his ability to smell and actually bite.
Again, the local fauna would be more usefull here, given that it is - quite literally - adapted to the world.
The Cybernetic way
This would be a later/GR era technology. Instead of making a Robot warrior with AI, why not put a human brain into a Robot Warrior Body?
Or a Dog Brain into a Robo-Dog body?
In a way, even the Warhammer 40k Servitor counts. And they also got Cyber-Mastiffs. It could even be a vat-grown brain
This option is usually picked because you either could not make a AI - but had the cyber interface technology - or because you are fighting AI.