252. Evaluation of Phytase Inclusion on Tissue Accretion in Pigs Fed Phosphorus Deficient Diets

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Abstract Phytase is commonly added to swine diets to help improve phosphorus availability, bone mineralization, and to reduce inorganic phosphorus supplementation. Our objective was to evaluate lean, fat and bone tissue accretion in pigs fed diets deficient in phosphorus and increasing levels of phytase. Forty mixed sex pigs (9.41 ± 0.3 kg BW) were assigned to individual pens and one of four treatment groups for a 42-day study. Diets were corn–soybean meal–based mash and formulated to contain 0.09 to 0.40% available phosphorus (avP). The dietary treatments were: 1) No added monocalcium phosphate or phytase (0.09% avP, phosphorus deficient), 2) Treatment 1 with the addition of 500 FTU/kg phytase (0.24% avP), 3) Treatment 1 with the addition of 2,000 FTU/kg phytase (0.34% avP), and 4) Treatment 1 with the addition of monocalcium phosphate (0.40% avP, phosphorus adequate). Diets were all isocaloric and calcium was formulated to 0.78% in all diets. Pig body weights and feed disappearance were recorded at the beginning and end to calculate ADG, ADFI, and feed efficiency (G:F). On day 42, all pigs were scanned using a dual-energy x-ray absorptiometry (DXA) to analyze whole body lean, fat, bone mineral content (BMC), and bone mineral density (BMD). All data were analyzed in R with pig as the experimental unit. Final body weight increased linearly as avP increased from 0.09% to 0.40% (22.8, 29.1, 33.1, and 35.1 kg, respectively; P < 0.001). Average daily feed intake in the 0.09% avP diet was 0.73 kg compared to 0.99, 1.21, and 1.14 kg (0.24%, 0.34%, and 0.40% avP diets, respectively; P < 0.001). Additionally, GF increased linearly as avP increased (0.52, 0.58, 0.57, and 0.65, respectively, P < 0.001). Over the 42-d period, whole-body lean tissue accretion increased linearly as avP increased (330, 483, 570, and 625 g/d, respectively, P < 0.001). Moreover, fat accretion increased linearly as avP increased (67.2, 98.3, 103.5, and 113.1 g/d, respectively; P = 0.001). In the 0.09% avP diet, BMC accretion content was -1.28 g/d, compared to 0.52, 3.61 and 8.36 g/d (0.24%, 0.34% and 0.40% avP diets, respectively, P < 0.001). As dietary avP% increased, whole body lean tissue mass as a proportion of total mass remained unchanged (81.2, 81.5, 81.6, and 81.6 %, respectively; P = 0.882), whereas BMC mass as a proportion of total mass increased linearly (0.64, 0.72, 0.95, and 1.36 %, respectively; P < 0.001). In conclusion, compared to pigs fed phosphorus deficient diets, 500 and 2000 FTU phytase improved pig body weights, lean and bone mineral accretion. However, increasing dietary phytase alone was insufficient to maintain equal performance to that of pigs fed adequate phosphorus.

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