Efficacy of different levels of a cholecalciferol 25-OH-derivative in diets with two limestone forms in laying hen nutrition

An experiment was conducted on 180 Hy-Line Brown hens (from 26 to 70 weeks of age) in a 5 x 2 factorial arrangement with five levels of vitamin D 3 and 25-OH-D-3 derivative rations and two forms of limestone in the diet. Diets were supplemented with 1500 IU of vitamin D-3; vitamin 25-OH-D-3 derivative was substituted for cholecalciferol in amounts equivalent to 0, 25, 50, 75 and 100%. Limestone (8.5% in the diet) was supplied in fine pulverized (LF, 0.1-0.4 mm) or mixed: fine + grit (LG, 2-4 mm) form as a 1: 1 mixture of LF:LG. Eggshell quality, tibia bone breaking strength and performance indicators were studied. Supplementation of the diet with LF + LG limestone decreased feed intake and, at 70 weeks of age, increased eggshell breaking strength and tibia bone strength in comparison with group LF. At 66 weeks of age, hens fed 25% of vitamin D-3 as 25-OH-D-3 laid eggs with thicker and denser shells. At 66 and 70 weeks of age, partial or complete substitution of cholecalciferol with 25-OH-D-3 increased eggshell breaking strength. The effect of 25-OH-D-3 on bone breaking strength was not confirmed statistically. Under the conditions of this experiment, simultaneous use of LF + LG and 25-OH-D-3 in the diet for older layers appears to be the most efficient combination for achieving high resistance of eggshells and tibia bones.