Effect of microbial phytase, vitamin D 3, and citric acid on growth performance and phosphorus, nitrogen and calcium digestibility in growing swine

Abstract

Two experiments were conducted to determine the effects of feeding microbial phytase, vitamin D 3 and/or citric acid on grower pig performance and nutrient digestibility. In experiment 1, 30 crossbred pigs (23.4 kg) were fed one of five diets during a four week trial. The basal diet (negative control) was based on corn and soybean meal and contained 6.9 g kg −1 calcium, 551 IU vitamin D but no inorganic phosphorus (3.2 g kg −1 total phosphorus). The experimental diets were supplemented with either vitamin D 3 (2000 IU kg −1), phytase (750 phytase units kg −1) or both. A positive control diet, containing monocalcium phosphate to supply a normal phosphorus level (5.1 g kg −1 P), was also used. Daily gain, feed intake and feed efficiency of pigs fed a low phosphorus diet were improved by the addition of phytase ( p<0.05). Serum phosphorus was increased and alkaline phosphatase activity was decreased ( p<0.05) by the addition of phytase. Pig performance was not improved by supplementing vitamin D 3 (+2000 IU kg −1) but serum phosphorus increased and alkaline phosphatase activity decreased. Addition of vitamin D 3 (+2000 IU kg −1) to the diet containing phytase tended ( p>0.05) to increase pig performance. In the second experiment, 12 castrates weaned at 28 days of age were used in a 6×6 incomplete latin square design experiment involving six diets. A corn-soybean meal basal diet, containing no inorganic phosphorus, provided 3.8 g kg −1 total phosphorus. The experimental diets were similar to the basal diet but were supplemented with phytase (750 phytase units kg −1) alone or in combination with either 15.0 g kg −1 citric acid or 2000 IU kg −1 of added vitamin D 3. An additional diet provided all three additives in combination while a positive control diet, containing 10.6 g kg −1 dicalcium phosphate, was formulated to provide 5.6 g kg −1 total phosphorus. Each pig was housed in a steel metabolism cage and fed a restricted quantity of feed, three times daily. The apparent digestibility of dry matter, phosphorus and calcium was significantly ( P<0.05) improved by the addition of phytase. The addition of vitamin D and/or citric acid tended ( p>0.05) to further increase the digestibility of these nutrients. Nitrogen digestibility was increased ( p<0.05) by phytase in combination with vitamin D and/or citric acid but not when supplemented alone. Phosphorus excretion from pigs fed the low phosphorus (3.8 g kg −1 P) diet plus phytase, alone or in combination with citric acid or vitamin D, was 27% less than pigs fed the positive control diet. Fecal nitrogen excretion was 8.3% lower for pigs fed phytase compared with the positive control diet while further reductions were obtained when fed in combination with citric acid or vitamin D. These results indicate that the addition of phytase, to a corn-soy diet containing no inorganic phosphorus, liberated enough phosphorus from phytate to allow pig performance similar to that achieved with a diet containing supplemental inorganic phosphorus. There was no further increase in the effectiveness of phytase as a result of the addition of vitamin D 3 and/or citric acid.