Calcium and Phosphorus Metabolism and Eggshell Thickness in Laying Hens Producing Thick or Thin Shells

Abstract

Two experiments were carried out to investigate the Ca and P metabolism of hens laying thick- (THK) or thin-shelled (THN) eggs on shell-forming days (SF) and days on which shell formation does not occur (NSF). In Experiment 1, 10 hens identified as producing THK or 10 hens producing THN eggs were offered a diet containing 3.5% Ca and .4% available P. Feed consumption, egg production, egg weight, egg deformation, and shell weight were recorded over 8 days. Shells and excreta were collected daily for Ca and P analysis. Feed, Ca, and P intake did not differ significantly (P>.05) between the two groups of hens, however, feed intake and Ca retention increased significantly (P<.05) on SF compared with NSF days. The THK hens retained significantly (P<.05) more Ca compared with THN hens. No differences (P>.05) were recorded for egg production, although there were differences (P<.05) in egg weight and shell deformation between the two groups of hens. Increased egg weight did not account for differences (P<.05) in eggshell deformation. Although percentage shell Ca was not significantly different (P>.05), total shell Ca was different (P<.05) between the two groups.In Experiment 2, both groups of birds (THK and THN) were allowed simultaneous access to two different diets, a high-energy, high-protein diet low in Ca and P, and a low-energy, low-protein diet high in Ca and P. There were no significant (P>.05) differences in feed intake on NSF versus SF days, however, feed intake was significantly (P<.05) different between the two groups of birds. There were no differences (P>.05) in Ca and P intake or retention for SF versus NSF days nor between THK and THN hens. Although there was no difference (P>.05) in P intake or P retention between the groups, P retention did decrease significantly (P<.05) on SF compared with NSF days. Although egg production and egg weight did not differ (P>.05) between THK and THN hens, eggshell deformation, shell weight, and grams of shell Ca did differ significantly (P<.05) between the two groups of birds.