Observations on the calcium balance of laying hens

Two groups of Single Comb White Leghorn pullets, 4 months of age, were fed 1·85 and 2·70% calcium in the diet, respectively, for twelve consecutive periods, each consisting of 4 weeks. Records of egg production and egg weight were kept throughout the entire experiment for each hen. Calcium balance and egg-shell quality studies were conducted with 16 pullets for 5 consecutive days out of each 28-day period. A highly significant difference between the lots favouring the high-calcium birds was found in egg production, shell weight, and calcium retention. There were no significant differences between the lots in percentage calcium retention, food consumption, and body weight. The high-calcium group was shown to retain more calcium from the feed and excrete more calcium through eggs. Calcium retention and percentage calcium retention increased upon commencement of egg production to reach a maximum at the second period of production. Both remained fairly constant thereafter. The hens went into negative balance early in production and returned to positive balance during the later part of the first laying year. The return to positive balance could be explained by an increase in calcium retention and a decrease in egg production. There was no reduction in shell weight, or shell weight per unit surface area during the period covered by this trial.