| The first two studies were designed to evaluate the effects of a bacterial phytase (Exp 1 and 2) and a fungal phytase (Exp. 2) on nutritional and physiological responses in weanling pigs. Pigs were weaned at 21d of age and housed individually. Treatments consisted of a negative control diet (0.45% total P and 0.14% available P) supplemented with either 0, 500, 1,000 and 2,000FTU/kg of phytase and a positive control (PC) diet without phytase (0.6% total P and 0.29% available P). In Exp 2, treatments were the same as Exp. 1, with the addition of a fungal phytase at 500 and 1,000FTU/kg. In Exp 1, supplemental phytase increased bone ash % (P=0.01). Pigs fed the PC diet also had a higher bone ash (P=0.01) than pigs fed the NC. Pigs fed phytase had a linear increase in G:F (P=0.03). Pigs supplemented with phytase also tended to have an increase in the gene expression of chymotrypsinogen. In Exp 2, pigs fed the PC diet had a higher bone ash than pigs fed the NC diet (P=0.01). There was also a linear increase for both phytases in bone ash. The A. niger phytase had a quadratic effect on ADG ( P=0.04) and G:F (P=0.02) as phytase was added in the diet. When comparing the PC and NC, the PC tended to increase ADG ( P=0.09) and G:F (P=0.09) than NC. The third study was designed to determine the effect of high levels of phytase on performance of weanling pigs that were challenged with Escherichia coli F18. Pigs were weaned at 21d and were assigned to 1 of 6 dietary treatments arranged in a 2 x 3 factorial randomized complete block design. The 36 pens were held in 2 separate barns, 1 for the control group and 1 for the challenged group. Factors consisted of: 1) disease challenge status and 2) dietary treatments (a control diet with adequate phosphorus at 0.60% total P, 0.29% available P, a diet with 0.45% total P and 0.14% available P and 500 phytase units, and a diet with 2,500 phytase units). After 2wk, pigs were either challenged with E-coli or not and placed in experimental pens. Because of contamination, 22 pens were used as "challenged" pens and 14 were used as control pens. During the third weigh period (d10 to 17) there was an interaction between disease and phytase (P=0.01) indicating lower growth rates in healthy pigs fed 500FTU/kg of phytase. Phytase or disease had no other impact throughout the study. The fourth study was designed to measure the ability of an E. coli phytase to improve the bioavailability of P using a slope ratio assay in nursery pigs. Pigs were weaned at 21d and fed a common diet for 14d. Dietary treatments consisted of 1) a NC diet which was deficient in P (0.55% and 0.17% Ca and available P respectively), 2) NC diet plus 0.075% additional P, 3) NC diet plus 0.15% additional P, 4) NC diet with 250 FTU of phytase, 5) NC diet with 500 FTU of phytase, 6) NC diet plus 1000 FTU of phytase. Bone ash also had an estimated available P equivalence of 0.051, 0.071, and 0.117% for 250, 500, and 1,000FTU/g respectively. Bone P had an estimated available P equivalence of 0.041, 0.088, and 0.146% for 250, 500, and 1,000 ftu supplementation levels, respectively. Serum P had an estimated available P equivalence of 0.066, 0.106, and 0.128% for 250, 500, and 1,000ftu supplementation levels, respectively. There was an estimated available P equivalent foce apparent fecal digestibility of 0.030, 0.046, and 0.090 for 250, 500, and 1,000 ftu supplementation levels, respectively. |
