Influence of time of calcium intake on bone and dietary calcium utilization

Sixteen hens, 67 weeks old, having oviposition times at 0700 +/- .25 hr, were used in Experiment 1. Hens were randomly divided into two treatments and fed a .08% calcium diet following oviposition. For 5 days, at either 0800 (AM) or 1600 (PM) hours, hens received 3.65 g of calcium by intubation. On Day 1, the calcium source contained 25 microCi of calcium-45 (45Ca). Eggs and excreta were collected daily for 45Ca analysis. Experiment 2 was similar to Experiment 1 except that 34-week-old hens were used. Calcium-45 activity of the egg shell, excreta, serum, and total contents of the gastrointestinal (GI) tract was determined. Results of Experiments 1 and 2 indicated that hens receiving their daily supply of calcium in the PM deposited significantly more of that day's dietary calcium on the following day's egg than hens receiving calcium in the AM. Excreta from the AM-treated hens contained significantly more 45Ca than that from the PM-treated hens during the first 24 hr in both experiments. In Experiment 2, the quantity of 45Ca in serum and GI tract contents was significantly higher from hens in the PM treatment. It was concluded that hens utilized significantly more calcium for egg shell formation from PM consumption rather than AM consumption and, therefore, were less dependent on bone reserves when the calcium was consumed in the PM.