Effect of Various Calcium:Phosphorus Ratios at Low and High Dietary Phosphorus for Starter, Grower and Finishing Swine

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Abstract
Three 2 × 4 factorial randomized-block design experiments were conducted to evaluate the effects of various Ca:P ratios (1.3:1, 2.0:1, 3.0:1, 4.0:1) at two dietary P levels (.05% below NRC, .10% above NRC) on growth, serum mineral and bone measurement characteristics in starter, grower and finisher swine. Experimental diets were formulated using corn and soybean meal with total dietary Ca and P levels adjusted using limestone and dicalcium phosphate at the expense of cornstarch. Pigs fed low P diets displayed a trend toward lower daily gains and higher feed conversions after the Ca:P ratio exceeded 1.3:1, whereas when high dietary P was provided, adverse effects on performance were not observed until the Ca:P ratio exceeded 2.0:1. Serum Ca concentrations were higher (P<.01) and serum P lower (P<.01) with increasing Ca:P ratio, with the response more pronounced at low dietary P levels. Percent bone ash decreased as Ca:P ratio widened during the starter (P<.01) and grower (P<.01) production phases, with finisher-phase bone ash demonstrating a minimal response. Dietary P level had a greater effect on percent bone ash than Ca:P ratio, with high dietary P resulting in increased percent bone ash in the starter (P<.01), grower (P<.01) and finisher (P<.01) phases. Bone-bending moment and bone stress were higher at the high dietary P level in grower (P<.01) and finisher (P<.01) phases, whereas bone-bending moment and bone stress declined during grower (P<.05) and finisher (P<.05) phases, respectively, as Ca:P ratio widened. Bone wall thickness increased (P<.01), but inside bone diameter decreased (P<.05), with high dietary P. Wider Ca:P ratio resulted in decreased bone wall thickness in both grower (P<.01) and finisher swine (P<.10). These results suggest that high Ca:P ratios can adversely affect swine performance and bone development during each production phase. When low dietary P is provided, Ca:P ratios above 1.3:1 resulted in decreased growth and bone development, whereas when high dietary P levels are provided, detrimental effects were not exhibited until the Ca:P ratio exceeded 2.0:1. Copyright © 1986. American Society of Animal Science. Copyright 1986 by American Society of Animal Science.

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