175 Effects of increasing calcium to available phosphorus ratios in diets containing phytase on growth performance and bone mineral content of nursery pigs

Abstract

The objective of this experiment was to evaluate the growth performance of nursery pigs in response to increasing total calcium to available phosphorus (aP) ratios in diets containing phytase (250 FTU/kg, Natuphos E, BASF, Florham Park, NJ). A total of 480 nursery pigs (BW=5.74 ± 0.62 kg; L337 X Camborough, PIC, Hendersonville, TN) with 10 pigs/pen and 7 pens per treatment (6 pens fed 2.75:1 diet) were allotted to 7 treatments consisting of increasing ratios of calcium to available phosphorus: 1.25, 1.50, 1.75, 2.00, 2.25, 2.50, 2.75. From d-7–0, pigs were fed a common diet. They were then fed the treatment diets during two experimental phases from d1–14, and d15–28, respectively. Available P was formulated to 0.33 and 0.27% (about 90% of requirement) in dietary phases 1 and 2, respectively. Body weight, ADG, ADF and G:F were determined. Mineral content of the femur was measured on d 35 on 1 pig per pen using DXA procedures. Data were analyzed as repeated measures using PROC MIXED (SAS, 9.3). Orthogonal polynomial contrasts were used to determine linear and quadratic effects of increasing the Ca:aP ratio. Increasing Ca:aP resulted in a linear decrease in ADG (353, 338, 328, 304, 317, 291, 280 g/d; P < 0.01), ADFI (539, 528, 528, 500, 533, 512, 489 g/d; P < 0.05) and G:F (0.68, 0.66, 0.64, 0.62, 0.61, 0.59, 0.58; P < 0.01). Increasing Ca:aP also resulted in decreased BW on days 14 and 28 (P < 0.01). Bone mineral content (BMC) decreased with increasing Ca:aP ratio (6.2, 6.3, 5.7, 5.9, 5.5, 5.6, 5.3 g; P < 0.05). In conclusion, all outcomes indicated that any level of calcium above the minimum used in this experiment impaired growth performance and skeletal development. Additional, longer term studies are required as these results were unexpected.