The Effect of Citric Acid, Phytase, and Their Interaction on Gastric pH, and Ca, P, and Dry Matter Digestibilities

Purdue University 2002 Swine Research Report. Organic acids have been supplemented to weanling pig diets in an attempt to improve postweaning lag. Organic acids have proved beneficial in improving average daily gain (ADG) and increasing nutrient digestibility (Falkowski and Aherne, 1984; Edmonds et al., 1985; Geisting and Easter, 1985). There has also been interest in acidifying grower pig diets in an attempt to increase ADG and improve feed efficiency, but results are variable. Some studies report positive effects on ADG and feed efficiency (Jongbloed et al. 1996; Kirchgessner and Roth, 1989; Kirchgessner and Roth, 1990) while others do not (Thacker and Bowland, 1980). Typically, a decrease in stomach pH is observed with acid addition (Sciopioni et al., 1978; Radcliffe et al., 1998; Burnell et al., 1998; Rice et al., 1999). However, the majority of reported research on stomach pH provides data taken at only one point in time, at slaughter, and it is difficult to understand the effects of acid on stomach pH over time or the stress of slaughter influencing stomach pH. There has been recent interest in combining acid and phytase to investigate possible interactive effects. Microbial phytase has two optimal peaks of activity at pH 2.5 and 5.5 (Simmons et al., 1990), and the stomach pH of a pig varies from 1.0 to 4.5 (Chesson, 1987). Phytase activity changes along the digestive tract, with the most efficient hydrolysis of phytate by phytase occurring in the stomach (Yi and Kornegay, 1996; Mroz et al., 1997). It is hypothesized that by adding acid and phytase in combination, the stomach pH would decrease and create a more optimal environment for enzyme activity. It also seems plausible that by acidifying the diet, gastric emptying might be slowed, which in turn would alter nutrient digestibility. However, research in this area is scarce. Our objectives were to determine the effects of organic acids alone or in combination with phytase on stomach pH over time, rate of digesta passage, and nutrient digestibility.