I was thinking that perhaps animals could be trained in different ways. Specifically two options:
Raise a Feed Animal: This option will allow you to expend a unit of edible food (for that animal's type) and make the animal into a "Feed animal" ie "Feed Cow" Effectively, a feed animal becomes a size or two larger allowing it to produce more meat, fat, and bones when butchered. The higher quality of the training, the more the animal produces relative to its size. This would give your animal trainer a more domestic use than training animals of destruction.
Train a Pack Animal: This task would give the creature the ability to act as hauler for any number of goods. A pack animal could be assigned to a hauler and will follow the hauler and pick the same type of goods that the hauler has tasked. The higher the quality of training the animal gets the stronger and tougher it becomes, allowing it to hold more weight. Additionally, the quality can affect personality traits that dictate the animal's work ethic, stubborness, and the time it takes to make pathfinding decisions.
If quality isn't really a hidden factor in animal training, it should be. For example, a legendary trainer should be able to train better war dogs than a novice. War dogs would be faster, stronger, tougher, and get a damblock bonus based on quality level. Hunting animals could have sharper senses and be able to detect hidden units from farther away or have more agility and greater ambush skill. Also, a well-trained animal could also be a point of admiration for fortess-dwellers. You could have thoughts like: "Tobol Smashedbins admired an excellently trained war dog lately. Tobol Smashedbins admired his own highly trained pack mule."