Excessive cholecalciferol in a layers diet: decline in some aspects of reproductive performance and increased bone mineralisation of progeny.

Feeding hens a diet containing 5,000 micrograms (200,000 ICU)/kg of cholecalciferol for four 28-d periods had no adverse effect on hen-day egg production or hatchability. Egg weight, shell quality, food consumption and fertility were significantly decreased in hens fed 5,000 micrograms/kg. of cholecalciferol compared with those fed 24 micrograms (960 ICU) cholecalciferol/kg diet. Plasma calcium increased significantly as the concentration of cholecalciferol was increased in the diet. However, no histologically detectable changes in the viscera or changes in the proportion of bone ash were observed with any concentration of the vitamin. Chicks hatched from dams receiving excessive doses of cholecalciferol (5,000 micrograms/kg) and maintained on a rachitogenic diet for 4 weeks had a significantly higher proportion of tibial ash but there was no effect on either body weight or tibial calcium.