Abstract
Though there is yet much to be learned about proper feeding of the hundreds of species of birds maintained and bred by the aviculturist, application of current knowledge could enhance the success of breeding programs. I believe that inadequate nutrition is one of the major factors inhibiting avian reproduction. Aviculturists can learn to recognize developing problems, and more importantly, act to prevent nutritional diseases. I shall describe a few nutritional and metabolic diseases that can be avoided.
METABOLIC BONE DISEASE
The metabolic bone disease complex is the winner in any contest of nutritional diseases most likely to interfere with avian propagation. "Metabolic bone disease" (MBD) is a term denoting a group of diseases, usually caused by inadequate dietary and husbandry managment, and characterized by metabolic defects affecting the structure and function of bones. MBD develops as a result of prolonged ingestion of a diet deficient in calcium and/or vitamin D; or a diet with an improper ratio of calcium to phosphorus. Many names have been given to the syndrome, including osteomalacia, osteoporosis, rickets, nutritional secondary hyperparathyroidisrn, cage layer paralysis, and fibrous osteodystrophy.
Clinical Signs of MBD
All birds are potentially susceptible to MBD, but certain groups are more likely to be fed inadequate diets. These groups include the carnivores, fruit eaters, and seed eaters, especially those consuming seeds with high oil content. Orphan birds are frequently affected.
In juvenile, growing birds, MBD is manifested as rickets, and characterized by stunted growth, bowing of the legs, swollen joints, spontaneous fractures, inability to perch and poor plumage development. Raptors fed an all meat diet may develop rickets in as short a period of time as 10-14 days.
Mature birds develop osteomalacia, or demineralization of bone. The clinical signs are usually more subtle and develop at a slower rate in adults as compared with immature birds. Nonetheless, the effects are severe.
Spontaneous fractures occur as a result of usually inconsequential trauma. Abnormal moults are common as moulting imposes a drain on calcium resources. Egg production may fail or soft shelled eggs are laid.
Other clinical signs include drowsiness, feather picking, regurgitation, excessive drinking, and loose stool. The loose stool may be caused by excess water intake, stirnulted by a need for increased urine flow to remove excess phosate.
Birds are also prone to hypocalcemic tetany Affected birds appear to be weak and drowsy. They may sway back and forth slightly on a perch until suddenly they fall either forward or backward. In some birds, the premonitory sign is wing fluttering. Startling the bird by opening a cage, or other activity, may precipitate a seizure. Usually in less than a minute the bird recovers from the seizure, but lies exhausted on the cage floor. Intervals between seizures may be minutes, hours, or days. A prolonged seizure may lead to death by preventing breathing.
Metablic processes
All animals require both calcium and phosphorus. Meeting the requirements of birds is especially critical because of the horrendous drain on calcium resources to form the egg shell. Failure to produce a normal egg obviously leads to reproductive failure.
The bird draws upon dietary calcium and calcium in a special type of bone called medullary bone to provide the calcium to form the shell. If dietary calcium is lacking, more will be drawn from the bone until the bone becomes soft and nonfunctional. Ultimately, egg laying ceases. In the immature bird, a similar deficiency of calcium prevents proper mineralization of growing bones (rickets).
The amount of calcium that can be absorbed is dependent upon the absolute amount of calcium in the diet, the presence of vitamin D and the ratio of calcium and phosphorus in the diet. Birds acquire vitamin 03 from the action of ultraviolet light on the skin of the feet, shanks and bare face. Ultraviolet rays can not pass through window glass, so glassed skylights or windows prevent the production of skinvitamin D3. Certain types of plexiglas do allow passage of U. V. light.
Too much phosphorus in the diet, common in both seed eaters and carnivores fed nothing but meat, tends to tie up the available calcium. A normal calciumphosphorus ratio, (Ca/P), is 2: I. A ratio of 1: 10 is commonly seen in seed-eater diets such as those to many of the parrots and 1 :20 in all-meat diets frequently fed to raptors.
For example, a 360-gm parrot could consume approximately 10% of its body weight or 36 gm of sunflower seeds daily. The sunflower seeds contain O. 17% calcium, which supplies 0.06 gm of calcium to the bird. If the bird is maintained on this unsupplemented diet, no medullary bone will be formed, it is highly likely that overt MBD will ensue. It is highly unlikely that ovulation can occur, but if ovulation does take place, 0. 78 gm of calcium will be expended to supply the shell for one egg. The 0.06 gm supplied in the diet falls far short of the requirement. Furthermore, the high oil content of sunflower seeds could further diminish the amount of absorable calcium because of the formation of insoluble calcium soaps in the intestine. The results of a total diet of sunflower seeds may be no eggs, or soft
shelled eggs, and MBD. I
It is not difficult to diagnose overt meta- . bolic disease using a combination of diet I evaluation, clinical signs and x-rays. Subclinical effects are hard to detect, but can be devastating to propagation attempts. It behooves the aviculturist to make certain the diet is balanced for calcium and that vitamin 03 is supplied.
A most important suggestion is to start chicks eating a wide variety of foods. Birds that become habituated to single food items are generally doomed to malnutrition, as was a hyacinthine macaw that would eat only coconut meat.
Look for a moment at the composition of a standard parakeet mix, Table 1. The calcium content and the Ca/P ratio are poor. Unless a calcium supplement is added, a bird fed this diet is liable to develop metabolic bone disease. Some calcium sources are listed in Table 2. Notice that some forms of calcium phosphate contain more phosphorus than calcium. Feeding such a supplement would be detrimental.