The Ability of Hens to Adjust Calcium Intake When Given a Choice of Diets Containing Two Levels of Calcium

Two experiments were conducted in which 270 hens received a choice of diets offered in two plastic cups. The treatments consisted of hens fed diets containing 3.0% calcium (Ca) in both cups, 6.0% Ca vs. 0.7% Ca, or 3.0% Ca vs. 0.7% Ca. Young hens exhibited the ability to discriminate between high and low levels of Ca. They greatly increased their consumption of the 3.0% Ca over the 0.7% Ca diet. Old birds showed an immediate marked aversion to the 6.0% Ca diet. They did not increase their consumption of the 3.0% Ca over the 0.7% Ca diet as did young hens. Reversing the position of the diets after the young hens' initial adjustment resulted in a reversal of the hens' positional preference for the feed. The birds tended to eat more of the higher calcium diet in the early morning and late afternoon, the times of greatest Ca need or anticipated need. This indicated that the young hens regulated their calcium intake according to metabolic need. Young hens in the regulating groups maintained egg production and egg weight, but not specific gravity of eggs nor serum calcium, at levels comparable to controls.