Effects of calcium diet supplements on egg strength in conventional and furnished cages, and effects of 2 different nest floor materials.

Several studies have demonstrated a greater incidence of cracked eggs in furnished than in conventional cages. Hens kept in furnished cages may have greater bone strength, so they may lay eggs with weaker shells because they may utilize more calcium for bone mineralization and less for shell formation. The effects of increased dietary calcium content were therefore studied in 3-hen conventional and 8-hen furnished cages. In addition, the effects of 2 different nest floor materials were studied in furnished cages. A total of 1,216 Lohmann Selected Leghorn hens were housed in either furnished or conventional cages and offered either the normal calcium supplementation used in commercial diets (37 to 40 g of calcium/kg) or increased calcium supplementation (44 to 50 g of calcium/kg) consisting of added limestone for 3 consecutive feeding phases of 20, 16, and 16 wk. Dietary calcium had similar effects in both cage systems. Greater limestone supplementation increased the laying rate (P < 0.05). Increased dietary limestone had no significant effects on egg quality, and no effects on tibia-breaking strength or specific gravity were observed. The laying rate was higher in conventional than in furnished cages (P < 0.05), but there was no significant difference between the cage types in terms of total egg mass produced. The cage type had no effect on tibia-breaking strength. However, the specific gravity and ash content of tibias were higher in hens kept in furnished than in conventional cages (P < 0.001). Based on this study, the weakening of eggshells in furnished cages is not caused by a possible calcium shortage resulting from high bone mineralization.