What you guys call marrow bones are actually the long bones in an animals leg. Usually the femur or humorus (is that it? I have temporarilly drawn a blank on anatomy) bones. The big ones in the upper legs connected to the shoulder and hip.
The best ones for my guys are the femur bones. I have a great butcher who saves them whole for me and cuts them how I want. They always have a good ammount of meat, tendons and ligaments on them which they love to chew off.
I have him cut the joint ends from the shank. An adult cows femur head is almost the size of my dogs head. and the knee end is about half that. The shank may be 3" thick and usually 7-8" long.
When I give them these types of bones, I usually let them chew for 1-2 hours, or until someone (James) gets tired, and then take them away. I can get 2-3 good chews out of them.
I have had these bones last pretty well once the dogs clean them off (several weeks), however, I found as you leave them out the bones minerals get harder and drier and instead of slowly grinding down they start to chip. Once I hear bones cracking I throw them away. I havent yet had any problems, but I have found large chips, that if ingested would probably be sharp (these are usually the type of pieces my dogs usually throw up a couple of days later). I also found when the bones were this hard, that is the most likely time my older dogs chip shards off their teeth. I started taking them away sooner... I seldom see this problem anymore (or puking bone chips).
Be VERY carefull with venison bones. The leg bones arent very thick and crack easily and the pieces are very sharp. I have seen how easily native americans could have used them as knives. They arent just pointy, they actually have an edge.
Large turkey bones are also best fed frozen so they chew up those bones more thoroughly. I fed them raw once and heard the bone crack, I took that leg away from Luke to look at it and saw how easilly they could swallow a sizeable piece when it is all kind of chewed into the meat. Especially if youd dog only chews it enough to bolt it down. When they are frozen they grind up the bones better.
Yes, I am paranoid. But when you have worked for a vet and seen these things from the inside...
Better safe than sorry.
My rule of thumb on size is...
once they are too small to easily hold with their paws to chew, they are gone. Especially foot, hoof and anke bones. Too small to hold and perfect choking size for medium to large dogs. Thick marrow bones that are cut too short (like from steak, or ham) also sometimes get stuck on dogs lower jaw when they try to lick out the inside. Saw that on a Rottie... he somehow got it all the way past his canines
, and it was on there good! Wire saw time!