The effect of disease, nutrition and management of egg and eggshell quality in laying hens.

Egg and eggshell quality were assessed under three different circumstances: challenge with infectious bronchitis virus (IBV) of complete-fed and choice-fed Isa Brown laying hens; the provision of calcium supplement in the form of either oyster shell or limestone chips and either choice-fed or included in a complete ration; a comparison of three different strains before, during and after an induced moult. The Isa Brown hens did not learn to choice-feed successfully. As a result, the choice-fed birds, which consumed protein concentrate in excess of feeding recommendations, laid heavier eggs with reduced eggshell quality and darker yolks. The eggshells of the complete-fed birds were darker and there was a significant transient decrease in the depth of the shell pigment in response to the IBV challenge. Calcium supplementation with ground oyster shell gave better eggshell quality than ground limestone and there were improvements in shell quality with higher levels of inclusion. There were strain differences in eggshell quality in the moult experiment. All strains showed a deterioration in eggshell quality as the birds were going out of production at the start of the induced moult. Eggshell quality improved following the moult, as evidenced by a significant increase in eggshell breaking strength.