In a nutshell, excess calcium over time causes kidney damage, can lead to gout and calcification of other organs and tissues. Excess has to be processed by the kidneys. Eventually kidney segments become atrophied and non-functional. There are 2 kidneys with 3 segments each. A bird can appear normal and continue laying while damage accumulates as long as there are 2 functioning segments. Once one of those last 2 segments fails, a chicken can die within 24 hours with the only symptoms depression, weight loss, darkened head, white pasty diarrhea, attempting to hide or simply sudden death. The truth is, most people with a bird that dies suddenly, shrug it off and don't get a necropsy - never suspecting diet.
http://poultryinfo.co.za/articles/Old/avian-urolithiasis-eng.pdf
Because of the high productivity of modern hens as opposed to jungle fowl, there is a complex relationship between calcium, phosphorus, vitamin D3 and the hormonal system of the layer in calcium metabolism during the lay cycle. Calcium and phosphorus balance is critical for proper egg production and eggshell quality. Layer ration should be formulated with correct amount of calcium and phosphorus (usually 3.5 - 4.0% calcium, 0.35-0.40% phosphorus
https://mikethechickenvet.wordpress.com/2012/07/10/bones-shells-and-hen-health/
Birds not building eggs shells daily, do fine on 1-2% calcium. 4% replaces that lost in the medullary bone when they deposit 2 grams of calcium in each egg shell. That 2 grams is the majority of the calcium in the bloodstream at any time.
Roosters, since they don't build egg shells are at particular risk. On breeder farms where roosters don't have separate feed systems, roosters die at 4 times the rate of hens due largely to lithiasis and gout.
http://www.thepoultrysite.com/articles/2337/urolithiasis-in-male-broiler-breeders/
http://www.poultryshowcentral.com/chicken_gout.html
http://poultryinfo.co.za/articles/Old/avian-urolithiasis-eng.pdf
Because of the high productivity of modern hens as opposed to jungle fowl, there is a complex relationship between calcium, phosphorus, vitamin D3 and the hormonal system of the layer in calcium metabolism during the lay cycle. Calcium and phosphorus balance is critical for proper egg production and eggshell quality. Layer ration should be formulated with correct amount of calcium and phosphorus (usually 3.5 - 4.0% calcium, 0.35-0.40% phosphorus
https://mikethechickenvet.wordpress.com/2012/07/10/bones-shells-and-hen-health/
Birds not building eggs shells daily, do fine on 1-2% calcium. 4% replaces that lost in the medullary bone when they deposit 2 grams of calcium in each egg shell. That 2 grams is the majority of the calcium in the bloodstream at any time.
Roosters, since they don't build egg shells are at particular risk. On breeder farms where roosters don't have separate feed systems, roosters die at 4 times the rate of hens due largely to lithiasis and gout.
http://www.thepoultrysite.com/articles/2337/urolithiasis-in-male-broiler-breeders/
http://www.poultryshowcentral.com/chicken_gout.html
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