Bullmastiffs are short haired dogs which means that they don’t require a lot of complex grooming, but they do shed a lot so you might consider brushing your dog’s fur every couple of weeks.
Even though while they are puppies there will really be no need to brush your dog’s coat it would be good if you did so every once in a while, just to get the dog used to being handled by you. He will get used to it much more easily while he is a puppy, and it will make your life much easier. You won’t have a problem making a small puppy be still, it might be much more difficult if you had to try the same with an adult animal that can weigh more than 130 pounds.
When brushing your dog you should use a soft pin brush and downward motions, starting at his hind quarters and moving towards the head. Be gentle, the dog might have small scabs that you wouldn’t want to upset. Brushing him is the perfect opportunity to check for ticks, parasites or skin irritations. Brush your dog as often as the both of you are comfortable with it, if you did it often enough he might even enjoy the massage that comes with it, and while it is not a health imperative for a dog to get brushed often, he will shed less hair in your house.
Sometimes you might want to accompany the brushing with a bath. You can soak the dog completely if you want, but the dry shampoo should usually do the trick. If you do decide to bathe him, just make sure that you have completely rinsed out the shampoo, because no matter how mild it is, if there is any of it left in the dog’s coat it will probably cause skin irritation.
You should also remember to every once in a while check his ears for inflammation and rinse them with antibiotic ear wash. Signs of inflammation are bad odor and redness. If you feel up to it you might also trim his nails, but that is something best left to the professionals.