The effect of cockle-shell grit, dietary level of calcium and EDTA on eggshell quality and laying performance of crossbred hens

Abstract

The eggshell quality and laying performance of White Leghorn x Australorp hens were measured in a 3 x 2 x 2 factorial experiment involving three levels (3.0, 3.5 and 4.0 per cent) of calcium, two calcium supplements (ground limestone and cockle-shell grit) and two levels (0 and 500 p.p.m.) of EDTA. The basal diet contained 14 per cent meat and bone meal as the sole protein supplement. Maximum eggshell quality was achieved on diets with 3.5 per cent calcium as ground limestone or 3.0 per cent calcium as cockle-shell grit plus ground limestone, respectively. Mortality increased with increasing levels of ground limestone in the diet. The dietary level of calcium had no effect on laying performance from 24 to 48 weeks of age but from 49 to 72 weeks of age, diets with 3.5 and 4.0 per cent calcium depressed rate of egg production (P < 0.05), hen-housed egg production (P < 0.01) and feed intake (P < 0.05) and increased mortality (P < 0.05). Egg weight, liveweight and feathering were not affected by calcium level in the diet but tibia-bone ash content was increased (P < 0.05) by the two higher levels of calcium. A daily intake of 3.5 g calcium per hen was adequate for maintenance of both eggshell quality and egg production. Compared with ground limestone, cockle-shell grit increased egg specific gravity (P < 0.05) and henhoused egg production from 49 to 72 weeks of age when the average daily maximum temperature was 27.2¦C. It also increased feed intake (P < 0.05), reduced mortality (P < 0.05) during the 24 to 48 weeks of age period, increased liveweight gain (P < 0.01), final weight (P < 0.05) and feather condition (P < 0.05). EDTA decreased eggshell weight (P < 0.05) and eggshell weight per unit area (P < 0.05).