Evaluation of a Dietary Phosphorus Depletion-repletion Strategy on Grow-finish Pig Performance

Abstract Dietary phosphorus depletion-repletion strategies have been employed to reduce environmental phosphorus excretion, without significantly impacting pig performance and bone health. This strategy relies on enhancing phosphorus retention and compensatory utilization for the restoration of bone mineralization and growth following a short period of depletion. Our objective was to evaluate a four-phase phosphorous depletion-repletion strategy on grow-finish pig growth performance. A total of 216 pigs (23.5 ± 2.28 kg BW; PIC 337 x 1050) were blocked by initial body weight and assigned to one of three dietary groups (n = 18 pens/treatment; 4 pigs/pen). Within each phase, corn soybean-meal based diets were formulated to be isocaloric, isonitrogenous, and equal in total calcium. Dietary treatments and digestible phosphorus (digP) for phases 1 and 3 were: 1) adequate digP utilizing monocalcium phosphate (0.30 and 0.21% digP; CON); 2) adequate digP utilizing 350 FTU/kg phytase (0.30 and 0.21%; PHY); and 3) deficient digP without monocalcium phosphate or phytase (0.10 and 0.09%; DEF). In phases 2 and 4, all pigs were fed a common replenishment diet supplemented with 1,500 FTU/kg phytase, formulated to 0.28% and 0.25% digP, respectively. Pig BW and pen feed disappearance were recorded at phase change to calculate ADG, ADFI, and feed efficiency (G:F) within each phase and overall. All data were analyzed using stats package in R with pen as the experimental unit with treatment and block as fixed effects. Overall pig removals and well-being were not affected by dietary strategy. In phases 1 and 3, the DEF treatment reduced pig BW, ADG, and G:F by 15%, 27% and 17% (P 0.001), compared to CON and PHY diets. In phase 2, DEF treatment ADG and G:F increased by 13% and 10% (P 0.05), compared to CON and PHY pigs. In phase 4, DEF treatment G:F increased by 10% (P = 0.01), compared to PHY pigs. Overall, CON had the highest ADG compared to PHY and DEF fed pigs (0.98 vs 0.93 vs 0.88 kg/d, respectively; P 0.001). However, no differences were observed for overall ADFI (P 0.05). Further, CON had the highest overall G:F compared to PHY and DEF pigs (0.39, 0.38 and 0.37, respectively; P = 0.001). At market CON BW tended to be greater compared to PHY and DEF pigs (127.3, 124.4, and 123.6 kg, respectively; P = 0.073). The DEF strategy increased total days on feed compared to CON and PHY pigs (114 vs 106 and 106 days, respectively; P 0.001). In conclusion, phosphorous depletion-repletion strategies could be used in grow-finish pigs. However, the duration and severity of phosphorus depletion and replenishment duration need to be optimized to mitigate growth and feed efficiency losses.