Circadian Rhythms of Serum Calcium in Hens and the Relationship of Serum Calcium to Shell Quality

A total of 860 Single Comb White Leghorn hens was used in four experiments in which 1060 blood samples were taken. The first three experiments were designed to establish a circadian rhythm for serum calcium, and to determine the effect of anterior heart puncture stress on serum calcium levels. The fourth experiment was designed to establish a diurnal serum calcium pattern for hens at time of oviposition, and to correlate serum calcium to shell quality and time of oviposition. A definite circadian rhythm for serum calcium was shown to exist on randomly selected birds. Serum calcium peaked at approximately 10:00 a.m. and 10:00 p.m., and troughed at 6:00 a.m. and 6:00 p.m. The stress of anterior heart puncture was shown to depress serum calcium levels by two mg. % for as much as 12 hours. The diurnal serum calcium pattern tended to level out when blood was taken only from hens immediately after oviposition. This indicates a positive correlation between serum calcium level and time of oviposition. Birds laying eggs with the best shell quality did not necessarily have the highest serum calcium values. Shell quality and serum calcium exhibit a very small negative correlation of –0.008. Time of oviposition and shell quality were positively correlated.