Calcium deposits typically take the form of bumpiness on an egg shell, with a feel like rough sandpaper. Sometimes calcium deposits are grainy and soft, and can be scraped off with a fingernail, while other times the calcium deposits are hard. In the latter case, chipping off the extra calcium usually weakens the shell in that spot.
Occasionally the chicken's reproductive system will go into overdrive. The result is two eggs forming at once. Normally, only one egg forms every 24 hours; when an extra one develops, some of the calcium from one shell can get misplaced and end up attached to the second shell. This results in one egg being laid with little or no shell at all and the other one being plastered with extra calcium.
Lack of Calcium
Calcium requires vitamin D3 for proper absorption. If your hen is lacking that vitamin, she might not be getting enough calcium in her system. Her body will store what little there is to salvage calcium for use by her bones and cells. A little more vitamin D3 in the chicken's diet usually solves the problem.
Illness and Prevention
Often, sick chickens will fail to produce quality eggs. Instead, they lay eggs with cracked, pitted, bumpy or thin shells. Illnesses can cause a hen to stop eating and drinking properly, which creates the lack of calcium in her diet. Bronchitis, laryngotacheitis and avian encephalomyelitis are three disorders that can cause a hen to lay eggs with calcium deposits on them. Proper vaccination of laying hens can reduce the conditions that create these difficulties.
Lighting and Water Supply
Strong egg shells require a certain amount of light each day, which is why egg farmers set up artificial lighting systems on timers in the chickens' living quarters. Adequate water is also necessary for every part of the chicken's body, including the reproductive system. Giving hens cool water works best to produce better and more eggs, while warm water in the hot months does just the opposite, and reduces the amount and quality of eggs laid.
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