I doubt if the FML was out more than an hour before I started getting lots of emails concerning body size and skeletal growth. Here are a few answers to many similar questions..... Osteoporosis simply means the bone is getting more porous; the amount of bone mineral declines and bone spaces become larger. In animals with large body weights, such as people, the risk of fracture and deformity becomes a problem. In lighter animals, such as ferrets, osteoporosis is not nearly as much of a problem, especially in terms of fracture. I called a few vets and the vet hospital and was told the risk of bone fracture due to ostoporosis in ferrets is limited to those with extremely advanced cases, which is uncommon except in conjunction with other diseases (usually kidney and related diseases). Osteoporosis can be caused by many factors--some of which are species unique--and beyond the scope of an FML post. But there are two factors that ferrets owners should be aware; neutering and exercise. Exercise is one of the best ways to increase the thickness and decrease the porosity of bone because as the muscles increase in size and strength, they cause biomechanical forces to stress the bone, which increases the deposition of bone minerals. In short, the more you exercise, the thicker and healthier your bones become. Neutering in females has the same type of effect as menopause; the loss of hormones inpairs the bone's ability to maintain itself, and the bone thins and becomes more porous. In males, neutering has two effects; first, it decreases the skeletal growth rate making the ferret smaller. Second, it also results in thinning and porous bone, but probably not to the same degree as in females. What does the ferret skeleton look like in neutered ferrets? I will describe a single bone, the femur (the other bones react similarly). In both male and female whole ferrets, the femur is a robust bone, and fairly thick compared to most other animals of the same weight and size, such as squirrels. Male ferret femurs are 15-30% larger than those from females. Femurs from early-neutered ferrets are substantially lighter, and somewhat shorter. Sexual dimorphism (females being smaller than males) still exists, but the males are only 5-17% larger, a significant decrease in dimorphism. Exams that test the density of the bone show a 10-25% loss of density, which means the bone is lighter and more porous. The differences are so significant to the trained eye that if you placed neutered and whole male skeltons on the table, I could easily separate them at a 95% or better rate. The same is true for females. In tests of mixed skeletons, I am just as good *IF* the skeletons are complete enough to allow sexing, but from individual bones, my success rate is about 85% because the whole females tend to overlap the neutered males in size. Most diets are fine for healthy adult animals. But sick animals have long been recognized as needing additional nutritional suppliments to "put the weight back on." The need for additional nutrients in growing animals has also been long recognized. Building bone is not much different from constructing a building; you need X amount of rebar (bone matrix) and Y amount of concrete (bone mineral). Limit any part of either, and you simply don't have enough materials to build the structure as high as you want it to go (skeletal growth). Only by providing the raw materials IN EXCESS of needs can you ever be sure of building the structure as high as possible by the contract deadline (growth period). In ferrets, this simply means the diet must contain slightly more protein, fat and bone minerals than the ferret can use; the rest just passes through in healthy animals. Notice I *DIDN'T* say carbohydrates? Kibbles are 60% or more carbohydrates, which means growing ferrets have to suck down a tremendous amount of food to equal the same intake of proteins, fats and bone minerals of animals eating a "natural" diet. That results in an increase in food costs, production of poopie, AND fatter ferrets. A person wrote to brag THEIR ferrets were 5 lbs, and attached a picture to prove it. The photo showed an obese ferret; my 5 pounders are quite lean. In fact, because muscle is heavier than fat, mine *look* 3-4 lbs, but are much heavier. Before Carbone went into rut, he topped 6 lbs. One of the ways I've found to make sure the ferrets maximize their skeletal growth is to feed them lots of chicken and turkey, including the skin, fat and bones. If you are afraid of bone splinters (I have *NEVER* had a problem in literally thousands of bone feedings), then instead of feeding them limb bones, feed them the neck and back bones WHICH DO NOT SPLINTER BUT CRUSH! My ferrets gnaw on these bones much like a dog, all my ferrets have strong, dense skeletons, and none of my carpet monkeys chew cloth, rubber, electrical cord or toys. BTW, chicken necks are the best! My ferrets LOVE them! Finally, once the skeleton has reached its adult size, the growth centers fuse and the bone can no longer grow. But it does continue to create new bone to replace older and dead bone, and ultimately the entire skeleton will be replaced, one osteon at a time. So adult skeletons are continually replacing themselves, but they don't grow. Placing a ferret older than a year on a "growth diet" will fail to make thier skeletons grow larger. One final myth to debunk. Eating bone is not the same as eating the "ash" found in most foods. Ash is the minerals left over when a carcass has been tested for composition and calorie value. True, it is mostly bone minerals, but bone can be a vastly different substance. With "ash," you have no idea of the chemical composition of the minerals, nor of their proportions. With fresh bone, you know the protein/fat/mineral content is perfectly balanced, as is the proportions of calcium to phosphate. Eating too much calcium OR phosphate can cause formation of stones, arthritic process and thinning of bones. But those problems do not exist when healthy ferrets eat bone where the minerals are proportional. Bob C and 20 Mo' Belching Bone Munchers [Posted in FML issue 2526]