Mundane beasts
The climate of the Empire ranges beneath the frigid cold of northern Wintermark and Varushka, through pleasant temperate areas such as the Marches and Dawn down to the warm grasslands of the Brass Coast. Summers are warm and dry, autumn and spring are wet and blustery, and winter is cold and often snowy.
Almost any mundane animal that might be expected to prosper in such environments can be found in the Empire, with the only major exception being that of the horse.
Oxen
The ox is the foundation of a lot of wealth, They have been used as domestic beasts of burden for thousands of years. These relatively placid animals are used to draw ploughs and pull wagons, and are kept for their flesh and leather. They are excellent beasts of burden and what they lack in speed and gracefulness they more than make up for in dogged determination. A man on foot can catch an ox-drawn cart even if it has a fair head start (as many fugitives have learnt to their chagrin), but they cannot be matched for sheer ability to move heavy loads over great distances. Working oxen require shoes, usually made by blacksmiths, which are very different to horse-shoes and require a lot more effort to get onto their cloven hooves.
Oxen in Play
These are the same beasts of burden used in our world for around six thousand years. Everyone from a Navarr Striding to a Freeborn trader uses wagons drawn by oxen. They are used in agriculture across the Empire, especially in Dawn and the Marches Nobody uses oxen for cavalry because they are entirely unsuited to it.
Horses
The horse is extinct in the Empire. While there are occasional stories that some have survived outside the Empire, their population was always small and nobody has seen a living example in four hundred years. They have become powerful symbols of the Empire, representing loyalty, strength, speed and fighting spirit. The Imperial Orcs especially use horse symbols, but they are visible on many Imperial buildings and important items.
Horses in Play
In the Empire world, the horse was never a widespread creature as it is in our world. Most people from outside the Empire consider the creatures entirely fanciful. It is fine to use horse images, as the horse is a potent symbol of the Empire, and to possess things that came from or were used with horses, provided they have been well preserved.
Mammoths
There are mammoths in Wintermark and there are known to be herds in Kalsea and a few herds as far south as Narkyst. They are also believed to live in Otkodov where they are extensively hunted by the barbarian orcs. They live in small herds, and are herbivorous. Attempts to domesticate them have proved largely fruitless; they are stubborn, willful creatures that pine and die when kept in captivity. They have been hunted since long before the foundation of the Empire by the Suaq people. A smaller cousin of the mammoth is known to exist in warmer climates outside the borders of the Empire called the elephant.
Mammoths in Play
These creatures are exactly what they seem to be: Mammoths. It is absolutely fine to have hunted them or to have items made out of their body parts. At this time, there are no domesticated mammoths or war mammoths used by Imperial citizens.
Dire Beasts
Some animals in the Empire grow to unusual size, reminiscent in some cases of prehistoric versions. There are dangerous cave bears, great cats with sword-like fangs, primaevil boars, prodigious crocodiles and immense walruses and massive wolves in the wild places of the Empire. Very large versions of less carnivorous creatures also exist - there are immense elk in parts of Varushka and Wintermark, huge cranes pick their way through the reedbeds of the Gancio, and great pale penguins haunt the southernmost reaches of Tsirku.
These creatures are uncommon; where they edge too close to civilisation they quickly become a problem that is addressed by armoured warriors. They are slowly being pushed into extinction, and encounters with them are rare, but they are a know threat of the wilderness. Other dire creatures are known to exist, and in larger numbers, in various places outside the Empire.
Dire Beasts in Play
These beasts are rare, but hardly unknown. A Test of Mettle can easily involve hunting one of these beasts, and a couple of Marchers with long spears might heroically defeat a dire boar in the woods of Upwold. It is fine to roleplay that your armour is made out of dire beast leather, or that the ivory for your wand came from a dire-lion's tusks.
Big Cats
Tigers are native to the foothills of Urizen, and there are some prides of lions on the pampas of the Brass Coast. The forests of Dawn and Varushka alike are haunted by large, dangerous cats similar to overgrown mountain-lions or wildcats. These creatures tend to stay away from humans except in rare cases where one develops a taste for human flesh.
Big Cats in Play
Big cats are more common than dire beasts. A lone character in light armour may receive a serious mauling from one of these creatures, and a fully-grown lion or tiger is more than a match for a single armoured knight. It is fine to roleplay that you have hunted them, and in some cases they may even be domesticated (although they do not travel well, and you cannot bring one onto the field at Anvil unless you can phys-rep it).
Dodo Birds
A particular delicacy is the dodo. This flightless bird is common along the coast of the Bay of Catazar and the animal has been domesticated by Brass Coast farmers. The flesh of the dodo is considered an especially tasty delicacy, and often forms the centrepiece of feasts in Dawn and Sarvos.
The dodo thrives in warm environments. They are flightless, and characterised in stories as slow witted, lazy and promiscuous.
Dodo Birds in Play
You can easily roleplay that chicken and similar white meat is dodo meat.
Beyond the Empire
While giraffes, elephants and the like are not indigenous to the Empire, they exist somewhere in the world. Almost any animal that could exist in the real world probably exists somewhere in the Empire world.