Internet Article: http://www.petcarevabeach.com/calcium.html
Referenced: 02/23/08
Author: Pet Care Veterinary Hospital
CALCIUM METABOLISM
Calcium is an essential mineral needed in everyday bodily functions. Most calcium is found within our bones and teeth,
but the small amount circulating in the blood stream and body fluids helps the body perform such vital functions as
muscle contractions, heart contraction, intestinal movement and nerve impulse conduction.
In most mammals the body has a system of checks and balances which keeps calcium at a steady, normal level in our
blood stream. Vitamin D and the hormones calcitonin and parathyroid hormone (PTH) all play a role. When the calcium
level drops low, PTH is released and stimulates the development of an active form of Vitamin D in the kidneys. This
Vitamin D then tells the intestines to absorb more dietary calcium into the bloodstream thus raising the levels. When
calcium levels rise, calcitonin is released promoting calcium withdrawal from the blood and deposition in bone, thus
keeping blood levels in a normal range. *1
Now, rabbits don't metabolize calcium like other mammals (aren't we finding out that rabbits do a lot of things different
from other mammals!). In the rabbit, the higher the dietary intake of calcium, the higher the level of circulating calcium in
the bloodstream. Therefore, rabbits that eat diets high in calcium will have proportionately higher blood calcium levels. So
what happens to all this excess calcium? It is excreted in the urine! Yes, rabbits will excrete up to 60 percent of their
ingested calcium in the urine (vs. other mammals which will excrete only 2 percent of ingested calcium in the urine).
That's why normal rabbit urine will look "cloudy" - this opacity is due to all the calcium carbonate crystals in the urine.
This syringe shows a rabbit’s urine with a significant amount of calcium-type crystals (figure 1). If this builds up in excess
it can cause a urine sludge syndrome as is seen in this rabbit having his bladder emptied and flushed (below)
On a radiograph (x-ray) the high degree of urine calcium crystals will show up light and outline the bladder. Some degree
of calcium buildup in the rabbit’s urine is normal but too much will predispose to infection and lead to trouble controlling
urinations.
So what does this mean to a rabbit's health? Well, that depends a lot on genetics, the individual rabbit, and factors we
still don't know about. The normally high urine PH of herbivores, such as rabbits, increases the risk of precipitation of
urinary calcium into stones or thick toothpaste-like deposits of calcium crystals known as sludge.*2 When a rabbit
develops bladder stones or sludge it will usually show signs of not feeling well. You may notice depression, lack of
appetite, weight loss, lethargy, thick creamy urine, straining to urinate, a hunched position, teeth grinding (indicating
abdominal pain) and urine scald of the skin around the prepuce or vagina. The rabbit will lose control of its normal
urinary habits and dribble urine, which keeps the fur around the perineum moist, thus leading to an inflamed dermatitis
or scald.*3
When these signs are seen, a trip to your veterinian is in order. Along with knowledge of the above history, a physical
exam, urinalysis, bladder x-rays and blood calcium levels will help your veterinarian make a diagnosis. Due to the high
levels of calcium excreted in the urine, many rabbits will have a small amount of calcium "sand"/crystals show up on a
radiograph.*3 Larger volumes of this crystalline sludge and actual bladder stones are not normal, and will be reflected in
the rabbit's overall disposition and health.
The diagnosis is made...now what can be done? The focus is now on treatment and prevention of recurrence. Treatment
involves ruling out underlying bacterial infection and treating with antibiotics. If bladder stones are present, surgery is
necessary to remove the offending, painful stone. If sludge alone is present, subcutaneous fluids are given on a daily
basis to increase urine output and "flush" the bladder. Also, manually expressing the bladder to expel the sludge helps
speed the process. In some rabbits, urinary catheterization under anesthesia is necessary to allow complete flushing of
the bladder.
Once the offending calcium sludge or stones are removed we focus on prevention. As mentioned earlier, a rabbit's blood
and urine calcium levels reflect dietary intake of calcium. Decreasing dietary calcium will directly lower serum calcium
levels and subsequently the amount of calcium excreted in the urine. To reduce calcium intake, grass hay (timothy, oat,
orchard grass) and green vegetables should be the primary diet and the amount of pellets reduced to 1 - 2 ounces per
day. Oxbow's timothy hay and high fiber Bunny Basics T pellets are both low in calcium and recommended. Oxbow has
been one of the only manufacturers to date to realize that basing a pellet on timothy vs. alfalfa is overall healthier for the
rabbit. In the vegetable arena, collards, chicory greens, lambs quarter, and mustard spinach are higher in calcium than
other choices and are best avoided. Please note, alfalfa hay is also high in calcium which is why we recommend the grass
hays.
The fiber rabbits need for nutrition, proper digestion and to aid in normal dental wear comes from feeding grass hays.
Variety is the spice of life and that includes the hay you feed your bunny. Oxbow Pet Products offers a variety of hays and
Pet Care Veterinary Hospital recommends the timothy, orchard grass, oat or botanical hays for the adult rabbit. Botanical
hay, Oxbow's newest variety, is a timothy hay with added dried herbs for flavor and so far our rabbit patients have given
it an overwhelming paws up!
So once again we see how important nutrition is and how proper nutrition in the form of high fiber, low calcium diets can
help keep a bunny's intestinal and urinary tract healthy and functioning properly.
References
Nutrition of the Domestic Rabbit
Laboratory Animal Science
P.R. Cheeke
Whary, Mart T., Peper, Randell L.
Calcium Carbonate Urolithiasis in a Rabbit
Laboratory Animal Science 1994
Paul-Murphy, Joanne
Urinary Tract Diseases and Disorders
Proceeding HRS Veterinary Conference 1998