Oyster shell is sometimes fed to chickens because it is an excellent source of calcium. Purina Mills® complete feeds are formulated to meet calcium requirements so supplemental oyster shell is usually unnecessary.
However, for older hens in hot weather, particularly those laying larger eggs, extra calcium may be beneficial. In this instance, a small amount of oyster shell can be fed at 1 pound per 100 hens daily. Over-supplementing with oyster shell should be avoided since too much calcium in the diet can lead to the same symptoms as a calcium deficiency and include weak or soft shells and reduced egg production.