Effect of limestone particle size on bone quality characteristics of hens at end-of-lay

A study was conducted to determine the effect of different limestone particle sizes in layer diets on bone quality characteristics at end-of-lay hens. Calcitic limestone (360 g Ca/kg DM) that is extensively used in commercial poultry diets was obtained from a specific South African source. Limestone particles were graded as small (<1.0 mm), medium (1.0 2.0 mm) and large (2.0 3.8 mm) and included (94.4 g/kg) into isoenergetic (14.3 MJ AME/kg DM) and isonitrogenous (172 g CP/kg DM) layer diets. Sixty-nine, individual caged Lohmann-Silver pullets, 17 weeks of age, were randomly allocated to the three treatments (n = 23) for the determination of various bone dimensional and mechanical properties at end-of-lay. At 70 weeks of age, 10 birds per treatment (n = 10) were randomly selected and sacrificed for the removal of tibia and humerus bones. Different limestone particle sizes had no effect on bone weight, length or diameter at 70 weeks of age. However, an increase in limestone particle size resulted in a significant increase in tibia breaking strength and -stress. These results suggested that larger particles limestone (>1.0 mm) have a beneficial effect on improving the mechanical properties of bone of older laying hens. ________________________________________________________________________________