Special Calcium Appetite in Laying Hens

Abstract

An experiment was conducted to study calcium appetite and dietary calcium level related to laying hen performance. The experiment consisted of three periods: pre-experimental, training, and experimental. A total of 80 commercial strain laying hens (58 weeks old) were divided into two groups. One group (20 birds) served as a control throughout the experiment and was fed 3.5% dietary calcium without a free-choice calcium supplement. The other 60 birds were randomly divided into 3 sets of 20 and were all fed 3.5% dietary calcium for a pre-experimental period (13 days) as an adaptation period to a new environment prior to a training period (5 weeks). Dietary calcium level was decreased by .5% each week through the 5th week (to 1% Ca) for all 60 hens during the training period. The birds were given access to a free-choice calcium supplement (calcium carbonate granules) during both the pre-experimental and training periods. This dietary regimen was used in an effort to allow all hens to adapt to a supplemental feeding program and be prepared or conditioned for sudden changes in dietary calcium level. At the end of the training period, the 3 sets of 20 hens were fed either 1, 3, or 5% dietary calcium and a free-choice calcium supplement for 6 weeks.As dietary calcium level was increased, there was a decrease in free-choice supplemental calcium intake; however, all birds (except controls) consumed very large amounts of calcium. The training procedure was successful: no hens rejected the supplement. Neither dietary calcium level nor total calcium intake affected feed intake. Hens that received the free-choice supplement produced significantly more eggs than the controls. There were no significant differences in eggshell strength, egg weight, or total plasma calcium; however, ionized blood calcium was significantly lower in some treatment groups than in the control group. The results showed that although these laying hens possessed a special appetite for calcium, they could not regulate calcium intake. As the level of dietary calcium was reduced, hens consumed larger quantities of free-choice calcium supplement; however, they appeared to have little or no ability or desire to reduce or stop consuming the free-choice calcium supplement even after their calcium requirements had been met. There was an indication that 3.5% dietary calcium may not be enough for optimum egg production from hens past 58 weeks of age.