Interactive effects of calcium and top-dressed 25-hydroxy vitamin D3 on egg production, egg shell quality, and bones...

Calcium and vitamin D are critical in attenuating metabolic Ca insufficiency often observed in older hens. We investigated interactive effects of dietary Ca and top-dressed 25-hydroxy vitamin D3 (25OHD3) on egg production, eggshell quality (thickness, EST, and breaking strength, ESBS), serum Ca, kidney, liver, and bones attributes in 74-wk old Lohmann LSL-lite layers. A total of 4 levels of Ca (3.0, 3.5, 4.0, and 4.5%) and 3 levels of 25OHD3 (0, 69, and 138 μg/kg) were tested. All diets had basal level of 3,300 IU of vitamin D3/kg, were allocated to 84 individually housed hens (n = 7), and fed to 81 wk of age. Dual-energy X-ray absorptiometry was used to measure bone mineral content (BMC) and density (BMD) in left ulna, femur, and tibia at week 74 (13 spare birds, baseline) and week 81. Birds fed diets containing 3.0, 3.5, 4.0, and 4.5% Ca consumed 3.4, 4.1, 4.2, and 4.8 Ca g/b/d. Interaction (P < 0.05) between Ca and 25OHD3 was such that 25OHD3 linearly increased egg weight and percentage of eggs graded as jumbo (≥70 g) at 3.0, 3.5, and 4.5% Ca levels. There was no interaction (P > 0.05) between Ca and 25OHD3 on the rest of the parameters. Calcium increased EST and ESBS quadratically (P < 0.05), EST increased with Ca intake up to 4.1 g of Ca/b/d whereas Ca intakes (3.4 and 4.8 g of Ca/b/d) had poor ESBS relative to intermediate Ca intakes. Kidney ash concentration increased linearly (P = 009) with Ca intake. However, BMC and BMD in ulna, tibia, and femur declined (P < 0.05) at week 81 relative to baseline. In conclusion, top dressed 25OHD3 linearly increased egg weight at various Ca intakes with no negative effect on eggshell quality or bone attributes. Feeding 4.1 to 4.2 g of Ca/b/d improved eggshell quality, however, higher intake deteriorated eggshell quality and increased renal ash accumulation with no benefit on skeletal integrity.