Some add charcoal in feeds but the question there is that charcoal might also absorb the nutrient the feeds provide for the animal and flush it with the feces of the animal.
Some give lactobacilli to the animal. They mix sugar, water and yakult then cover it, air tight/sealed then after 1 week this is what they add in the feeds of the animal.
You could try also to put charcoal to the feces of the animal to prevent it from smelling.
Water + manure = bad swell, if you will lessen the water that interact with the manure there would be less smell.