Title page for ETD etd-62597-112336


Type of Document Master's Thesis
Author Radcliffe, John Scott
Author's Email Address jradclif@vt.edu
URN etd-62597-112336
Title Quantifying the Effects of Microbial Phytase and Diet Acidity on Ca and P Utilization by Weanling Pigs
Degree Master of Science
Department Animal and Poultry Sciences
Advisory Committee
Advisor Name Title
Webb, Kenneth E. Jr.
Kornegay, Ervin T. Committee Chair
Harper, Allen F. Committee Member
Keywords
  • Rib Mineralization
  • Pigs
  • Phytase
  • Phosphorus
  • Calcium
  • Citric Acid
Date of Defense 1997-06-27
Availability unrestricted
Abstract
Five experiments were conducted, utilizing 512 crossbred weanling pigs to determine the P (Exp. 1) and Ca (Exp. 2 and 3) equivalency values of microbial phytase based on performance, rib mineralization and P and Ca digestibility estimates, and to investigate the possible interactions of phytase and citric acid (Exp. 4 and 5). In Exp. 1, adding phytase to low P diets linearly increased ADG (P < .001), rib shear force (P < .01), shear energy (P < .02), ash weight (P < .001) and ash percent (P < .001), Ca (P < .001) and P (P < .001) digestibility and digestible Ca (P < .001) and P (P <.001). Added P linearly increased ADG (P < .003), rib shear force (P < .003) shear energy (P < .001), ash weight (P < .001) and ash percent (P < .01), Ca (P < .02) and P (P < .001) digestibility and digestible Ca (P < .02) and P (P <.001). Based on phytase and P linear or nonlinear response equations for ADG, rib shear force, shear energy, and ash weight, P digestibility, and digestible P, the average equivalency of 500 U/kg of phytase was .78 g of P per kg of diet. In Exp. 2, dietary addition of phytase linearly increased rib ash % (P < .03), Ca (P < .001) and P (P < .001) digestibilities, and digested Ca (P < .001) and P (P < .001), but had no effect (P > .10) on ADG and rib shear force and ash weight. Added Ca linearly increased ADG (wk 3-4, P < .04), and rib shear force (P < .001), ash percentage (P < .001) and ash weight (P < .01), and digested Ca (P < .001), but P digestibility (P = .07) and digested P (P = .08) were numerically decreased. In Exp. 3, added phytase linearly increased ADG (wk 3-4, P < .002), feed efficiency (wk 3-4, P < .02), rib ash weight (P < .001), Ca total tract digestibility (P < .001), and Ca (P < .001) and P (P < .001) ileal digestibilities. Added Ca linearly increased ADG (wk 3-4, P < .02), feed efficiency (wk 3-4, P < .01), rib ash percentage (P < .001) and ash weight ( P < .001), shear force (P < .03) and energy (P < .008), and total tract (P < .001) and ileal (P < .001) digestible Ca. Based on phytase and Ca linear or nonlinear response equations for ADG in wk 3-4, measurements of rib mineralization, and digestible Ca, 500 U of microbial phytase was estimated to be equivalent to 1.08 g and .78 g of Ca in Exp. 2 and 3, respectively. In Exp. 4 and 5, dietary phytase addition linearly increased rib shear force (P < .004 and P < .02), shear energy (P < .001), dry bone weight (P < .001), ash weight (P < .001) and ash percent (P < .001). Calcium (P < .001) and P (P < .001) digestibilities were also improved in both experiments when phytase was added. Addition of citric acid in both experiments, reduced dietary pH and stomach digesta pH (P < .05). The addition of citric acid improved ADG (P < .05), feed efficiency (P < .04) and Ca digestibility (P < .05) in Exp. 4, but decreased Ca digestibility in Exp. 5 and had no effect on performance. In Exp. 5, the addition of 2.0% citric acid to the diet supplemented with 500 U/kg of phytase caused a decrease (P < .04) in the phytase activity recovered in the stomach digesta resulting in a phytase by citric acid interaction (P < .02). In summary, the addition of 500 U/kg microbial phytase to weanling pig diets, causes the release of approximately .78 g of P and .93 g of Ca, thus decreasing the need for supplemental P and Ca. The addition of citric acid to phytase supplemented diets does not appear to enhance the efficacy of microbial phytase based on the results of these studies.

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