Metabolic Bone Disease
Metabolic bone disease, or MBD, is a preventable problem that can occur in animals we rehabilitate. MBD has also been seen in wild animals with no prior human contact, though this is rare. A knowledge of this condition, and it's causes, can help us care properly for those species particularly at risk.
MBD is most often caused by improper diet. Vitamin D, which under normal circumstances the body produces on it's own (needing sunlight to do so), is vital to the body's ability to absorb calcium.
Sun received through windows and window screens is not adequate because these filter the important UV rays necessary for this to take place. Professionally formulated milk replacers have vitamin D in them, but as the animal is weaning they are receiving less and less of this vital nutrient so 20 minutes of full sun a day is recommended, or all spectrum or full spectrum bulbs can be used if the former is not possible. Because the formula we feed is balanced with *all* the vitamins necessary, the weaning diet is critical.
Since MBD can get started in as little as 5 days time, an animal that is not eating needs to be monitored closely. Often the signs are slight, and by the time it is obvious what is going on, correcting it becomes more difficult. MBD also affects the internal organs as well; so what we see on the outside is just the tip of the iceberg.
Some of the more subtle signs of MBD are excessive sleeping, not wanting to move around or jump and climb. MBD hurts! The bones (being effected the most), and muscles become weak and the animal is in pain. Swollen joints and improper bone growth (legs splaying in or out) are also sign of MBD's progression. In more drastic cases there are seizures and lack of use of the back legs. Because MBD is the thinning of the bone, a fall that would not normally have any effect can cause a leg or the spine to fracture or break.
One way to tell if you are dealing with MBD is a radiograph (advance cases) however the stress factor on the animal must be taken into account. The other is to watch how they move and observe their abilities. Can they hang upside down without discomfort? Are they using the full extension of their legs and body, (in other words moving *freely*)? It is important for you to know what *normal* is so that you can identify the possible onset of MBD in the early stages.
In rare cases, MBD is not caused by incorrect diet but by genetics. The body doesn't synthesize sun properly to create vitamin D, or the body doesn't process calcium correctly. While this is extremely rare, it has happened. Another possible cause of MBD, when a correct diet is being fed, is hierarchy. Even young animals have a pecking order and often the one at the bottom doesn't get the adequate food needed to keep calcium/phosphorus at the proper levels. Again, a good commercial diet that makes up 80% of their daily food will go a long way in preventing this. Monitoring weight gain, growth and overall heath will let you know if this is happening.
MBD can be treated, but the sooner it is caught the better. Correcting the diet, if that is the problem, is the first order of business. Adding additional calcium, along with making sure there is adequate access to vitamin D through natural sunlight or lighting mentioned above has proven to work well. Supplementing with actual vitamin D should only be done under the supervision of veterinarian, vitamin D is a fat soluble and can build up and become toxic, more is *not* always better. The most important thing to remember is an ounce of prevention is worth a pound of cure. In a perfect world Ca/pH should be at 2:1 and a good commercial diet, that is balanced, is the place to start. For the other 20% of the daily foods there are many dietary books on the market that will help you in keeping the Ca/pH ratios close to the acceptable level.
These are just the very basics and, depending on the severity of the MBD, other steps may also be necessary. If you have never dealt with MBD before it is important that you check with your veterinarian and/or another rehabilitator that is familiar with the problem and procedure.
It is important that we understand what part calcium and phosphorus play in the body. Below is a straight forward explanation of the very important rolls these two minerals, (also known as macroelements) have in bone growth and overall development of the animals in our care.
"They are major mineral constituents of the animals body and are largely associated with skeletal formation. Calcium is also important in blood clotting, excitability of nerves and muscles, acid-base balance, enzyme activation and muscle contraction, whereas phosphorus is involved in almost every aspect of animal metabolism, such as energy metabolism, muscle contractions, nerve tissue metabolism, transport of metabolites, nucleic acid structure, and carbohydrate, fat, and amino acid metabolism." Robbins, Wildlife Feeding and Nutrition Second Edition.
Metabolic Bone Disease (MBD) is a deficiency of calcium in a squirrel’s diet. It is caused by an improper diet wherein seeds, nuts, and corn are the major, or only, components of a diet. The condition will kill the squirrel. This is not a theory - it is common because some people ignore the warnings, do not follow the dietary instructions, give the animals a diet high in seeds, nuts, and corn, and low in calcium bearing foods. In addition to bone development, calcium is needed for all organic functions, including heart, respiration, blood circulation, muscle, and eyesight. Do not think you and your squirrel will be the exceptions if you feed a diet composed of seeds, nuts, and corn. This deadly diet is often sold in stores under the descriptor “Squirrel Feed”.
Seeds, nuts, and corn are high in phosphorous and contain low, or no, calcium (almonds and hazelnuts do have a small amount of calcium, but also contain phosphorous). The body needs phosphorous as well as calcium, but when phos ratios exceed calcium ratios, the phos blocks the absorption of calcium, making it unavailable to the body. If one feeds a low amount of high calcium foods, and a high amount of phos foods, it will cause mbd. Therefore, calcium foods must be the major component of the diet. Squirrels love nuts, seeds, and corn and will eat those foods exclusively if given the opportunity. When these foods are the major component of the diet, they are the nutritional equivalent of candy. When given as small portions of a diet, with high calcium foods being the major item on the menu, seeds, nuts, and corn become just one more nutritional element, in this case a positive element. Again: a diet of seeds, nuts, corn will cause metabolic bone disease if they are the major, or only, components of a diet.
Symptoms of MBD: general body soreness, activity levels decline, lethargy, sometimes a drop in appetite, sometimes labored breathing, increasing in severity to seizures and or paralysis, then death if not treated. The symptoms usually manifest around the age of 10 weeks; the caretaker may not see the symptoms, or recognize what he or she is seeing, until the symptoms become severe and the animal goes down. This is the point at which people usually call me crying, “something is wrong with my baby, he is paralyzed (or having seizures).” Some babies are dying in the person’s hands as we talk. This anguish is so preventable if one feeds a high calcium diet.