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CALCIUM - NEEDS AND DANGERS
By T. E. Roudybush, C. R. Grau
For Exotic Bird Report Number 7 (1/1/1987)

 

Calcium has been recognized as an essential element in the diet for almost 200 years. The first experiment to show this was reported in 1791 by Fordyce (1), who observed in his canaries that the hen “at the time of laying requires a quantity of calcareous earth, otherwise she is frequently killed by the eggs not passing forward properly.” We now recognize this as “egg binding”.

 

The main function of calcium in the animal is as a structural component of bone. Other functions include its need in blood coagulation, muscle contraction, myocardial function, and normal neuromuscular irritation. It is an important component of the intercellular cement which holds cells together. In birds, of course, calcium has the additional function of being the main mineral component of egg shells, which are almost entirely calcium carbonate, 40% of which is calcium. The calcium requirement for egg laying in a laying breed chicken is at least 100 times the requirement of the same hen when it is not laying. Because this remarkable change from a low to a high requirement may take place in less than a month, we are left with the difficult task of evaluating and expressing the calcium requirement of birds.

 

In a recent report, Blomquist (2) recommended levels of 1% calcium in the diets of mature nonbreeding pet and cage birds and 2.5% calcium for growing or reproductively active birds. Although no data were cited in support of these figures, it is likely that they are based on recommendations for egg-laying and rapidly growing chickens (3). There is now a body of evidence which indicates that these levels of calcium are well in excess of the requirement and that 2.5% calcium causes deleterious effects in growing birds.

 

Norris et al (4) found that adult White Leghorn male chickens were able to maintain bone calcium stores at 0.0025% calcium in the diet, but needed between 0.025% and 0.05% calcium to maintain normal plasma calcium levels and alkaline phosphatase activity. Rowland et al (5) found that non-laying White Leghorn hens were able to maintain bone strength at less than 0.02% calcium in. the diet. Both of these levels are well below the 1% recommendation of Blomquist (1).

 

For growing birds the National Research Council (3) recommends 1.2% calcium for turkeys from 0-8 weeks of age. This is the highest level of calcium recommended for any growing birds.

 

Several investigators who have fed levels of calcium above the NRC recommendations have observed deleterious effects. Smith and Taylor (6) fed chickens from 1 day to 10 weeks of age and found reduced body weights and feed efficiency at 1.35% calcium as compared with 0.83% calcium. Shane et al (7) fed diets containing 0.6% or 3.0% calcium to chickens between 8 and 12 weeks of age. The higher levels produced visceral urate deposits, mortality, nephrosis (kidney degeneration), and smaller parathyroid glands. Scott et al (8) cite experiments at Cornell University in which chickens 8-18 weeks old fed diets containing more than 2.5% calcium had 10% to 20% mortality with an incidence of nephrosis, visceral gout, and calcium urate deposits in the ureters. Within one to two weeks on the high calcium diets pullets developed hypercalcemia (high blood calcium) and hypophosphatemia (low blood phosphorus). Parathyroid size was reduced and its activity was greatly decreased. Feeding high levels of calcium reduced feed consumption and weight gain, and sexual maturity was delayed. Mortality from nephrosis continued from the growing period into the production period. On the basis of these severe effects, they recommended feeding not more than 1.2% calcium in the diet of growing chickens. After sexual maturity at 18-20 weeks of age laying chickens can tolerate higher levels of calcium (8). Woodard et al (9) found that pheasants, partridges and chickens fed 3% calcium and 0.3% phosphorus grew poorly, were severely paralyzed, and suffered high mortality. These levels are similar to those used successfully in the diets of laying hens.

 

From the evidence obtained by the several workers cited above, levels of calcium in excess of 1.2% of the diet were found to cause a variety of problems in growing birds. A recommendation of 2.5% calcium for growing birds is clearly in excess of the calcium requirement and is likely to cause severe damage and even mortality in growing birds.

 

For birds that are laying, a level of 2.5% calcium in the diet (1) would at first glance seem reasonable, because the NRC (3) recommends between 2.25% and 3.25% calcium in the diet for various breeds of poultry. However, altricial birds such as parrots, finches, and canaries feed their chicks the same diet which they themselves eat. In a flight with birds in various stages of reproduction it is not practical to feed a diet with a high calcium content to one set of birds and low calcium to another. Some aviculturists attempt to allow birds to balance their own calcium intakes by feeding calcium supplements such as pieces of oyster shell, limestone or cuttlebone along with a low calcium diet. There have been no controlled experiments of this method of calcium feeding so it is not possible to know whether parent birds may be overfeeding or underfeeding calcium to their chicks. Cage birds which incubate and raise their chicks do not usually lay as many eggs in a given time as do poultry kept to lay eggs to be incubated artificially. Thus the calcium requirement for egg laying may be expected to be lower in altricial birds than in poultry.

 

Recent studies in our laboratory indicate that sustained egg production in cockatiels can be achieved by feeding diets containing less than 0.5% calcium. A maximum level for reproduction has not been determined, but it is known that 1.0% calcium is satisfactory for both breeding and growing birds.


                                                          References
 
1.   Fordyce, C. 1791. Treatise on the Digestion of Food. (Second Edition). London (cited
      by McCollum, E.V., 1957, A History of Nutrition, p. 84—85. (Houghton. Mifflin,
      Boston).

2.   Blomquist, R. 1986. The effects of diet and calcium on pet bird health. Avian Rounds,
      vol. 5, pg. 7-9 (New York State College of Veterinary Medicine, Cornell University).

 

3.   National Research Council.1984. Nutrient Requirements of Poultry. 8th revised edition, National AcademySciences, Washington, D.C., 71 p.


4.   Norris, L.C., F.H. Kratzer, H.J.Lin, A.B. Hellewell and J.R. Beljan.1972. Effect of
      quantity of dietary calcium on maintenance of bone integrity in mature White Leghorn 
      male chickens. J. Nutr. 102:1085—1092.


5.   Rowland, L.0., Jr., D.R. Sloan, J.L. Fry and R.H. Harms. 1973. Calcium requirement
      for bone maintenance of aged non-laying hens. Poultry Sci. 52:1415—1418.

 

6.   Smith, H. and J.H. Taylor. 1961. Effect of feeding two levels of dietary calcium on the growth of broiler chickens. Nature 190:1200.


7.   Shane, S.M., R.J. Young and L. Krook. 1969. Renal and parathyroid changes
      produced by high calcium intake in growing pullets. Avian Dis. 13:558-567.


8.   Scott, M.L., M.C. Nesheim and R.J. Young. 1969. Nutrition of the Chicken. M.L.
      Scott and Associates, Ithaca, NY, 276 p.


9.   Woodard, A.E., P. Vohra, L. Snyder and C. Kelleher, Jr. 1979. Growth rate in three
       gallinaceous species fed diets inbalanced in calcium, phosphorus and protein. Poultry
       Sci. 58:687—693.