Dog is inhaling his food

of my 6 dogs 5 of them have been together since they were little, and about a month ago when they hit 6 months i started tying them out to feed to stop the fighting, they have all slowed down their eating, this dog is new to my pack so I am still learning him as his is still learning me, I am gonna try the smaller bowl and rocks thing first, sure hate to have to pour more feed to him if I dont need to, when he craps it is coming out like rabbit turds which makes me think he isnt digesting it well because he eats is so fast without chewing, which in turn would keep him from putting on weight. If you look at my other dogs they are fat compared to him and they are all within 6 to 7 lbs of him and being fed the same amount. He is supposed to be 2 but i think he is more like 18 months, the rest of my dogs are a year old or less