Adenosine triphosphatase in the uterus and duodenum of chicken hens during eggshell formation

Plasma calcium concentration and uterine and duodenal adenosine triphosphatase (ATPase) activities were determined during shell formation for high (H) and low (L) shell strength lines of hens selected from the last of four consecutive generations. The H and L lines were divided into three groups according to shell formation at 0, 15, and 22 h following oviposition. Plasma total calcium was determined from blood samples collected from the common carotid artery. Activity of ATPase was determined in uterine and duodenal mucosa. Shell strength, shell weight, percentage of shell per egg and shell thickness of the H line hens significantly exceeded those of the L line. During shell formation, no significant fluctuation in plasma calcium levels was observed within a line, but overall mean plasma calcium concentrations were higher in the H line than L line. Uterine ATPase activity increased with time after oviposition in both lines, with that of the H line being greater. Duodenal ATPase activity of H line hens remained fairly constant throughout the period, but this value showed fluctuations in the L line hens. It thus appears that laying hens with high and low shell strength may vary in their ability to use calcium for shell formation.