Two experiments using 413 crossbred growing-finishing pigs were conducted to assess the use of a commercial microbial phytase (Natuphos) in corn-soybean meal diets to improve phytate P bioavailability and thus reduce inorganic P supplementation and fecal P excretion. In Exp. 1 (n = 189), the following diets were used: 1) .50/.40% total P, respectively, for grower and finisher phases, and no phytase; 2) .40/.35% P and no phytase; 3) diet 2 plus 250 U phytase/kg; and 4) diet 2 plus 500 U phytase/ kg. The total Ca level was .58/.48% for diet 1 and .53/.43% Ca for diets 2, 3, and 4 in the grower and finisher phases, respectively. Feeding the low-P diet without supplemental phytase resulted in an overall 18% reduction in ADG (P < .05), 15% reduction in ADFI (P < .05), and 3% poorer feed efficiency (P < .08). Adding 250 to 500 U phytase/kg to the low-P diet restored ADG, ADFI, and feed conversion to levels not significantly different from and within 96% of that observed for pigs fed the adequate-P diet. The overall apparent digestibility of P was linearly (P < .01) improved with addition of 250 and 500 U phytase/kg to the low-P diet, but Ca and DM digestibilities were not affected by phytase or P level. In Exp. 2 (n = 224) the following diets were used: 1) .38/.33% total P, respectively, for grower and finisher phases, and no phytase; 2) .42/.37% P and no phytase; 3) .46/.41% P and no phytase; 4) diet 1 plus 167 U/kg phytase; 5) diet 1 plus 333 U/kg phytase; and 6) diet 1 plus 500 U/kg phytase. All diets contained .41/.36% Ca for grower and finisher phases, respectively. Pigs fed the low-P control diet grew slower (P < .01) and less efficiently (P < .10) than pigs fed diets with added P or phytase. With increasing levels of supplemental phytase or P there was a linear increase (P < .01) in ADG, digestibility of P, and digested P and a quadratic improvement (P < .05) in feed efficiency. Tenth rib mineralization based on shear force and ash were linearly increased (P < .08 to .001) as phytase or P was added to the low-P diet. There were generally no effects of P or phytase level on carcass quality. Using prediction equations derived from the response traits of ADG and P digestibility in Exp. 1 and ADG, P digestibility, and bone shear force in Exp. 2 to added phytase or P, we estimated that 500 U phytase released an amount of phytate P that was approximately equivalent to .87 to .96 g of P from dicalcium-monocalcium phosphate supplements. Fecal P excretion was estimated to be reduced 21.5%.

Four trials were conducted to examine concentration of zinc in tissues and performance of pigs fed high levels of Zn from ZnO, Zn-methionine, Zn-lysine, or ZnSO4. In Trials 1 (n = 80, 28 d of age, 7.5 kg BW), 2 (n = 80, 26 d of age, 7.1 kg BW), and 3 (n = 70, 23 d of age, 5.3 kg BW), pigs were assigned either to a control diet containing 105 mg/kg of Zn and 15 mg/kg of Cu or to supplemental dietary treatments of 3,000, 2,000, or 1,000 mg of Zn/kg of diet. In all three trials, dietary sources were ZnO, Zn-methionine, Zn-lysine, or ZnSO4. The trials lasted 2 wk. In Trial 1, performance of pigs generally was not improved by feeding 3,000 mg of Zn/kg from any of the Zn sources. Serum, liver, and rib Zn concentrations (P < .01) and liver Zn concentrations (P < .05) were greater for pigs fed the high Zn diets. In Trial 2, feeding high Zn did not affect overall performance. Pigs fed the high Zn diets had greater (P < .01) serum, liver, kidney, and rib Zn concentrations. In Trial 3, there were no differences (P > .10) in ADG or ADFI, but serum and liver Zn concentrations were greater (P < .01 and .05, respectively) for pigs fed high Zn diets. Within Zn sources, serum and liver concentrations of Zn were greater (P < .05) for pigs fed ZnSO4 rather than ZnO in Trials 1 and 2. In Trial 4 (n = 72, 7.1 kg), 25-d-old pigs fed diets containing 3,000 mg/kg of Zn from feed-grade ZnSO4, reagent-grade ZnSO4, or feed-grade ZnO in a 4-wk growth trial had similar ADG and ADFI, but the gain:feed ratio was lower (P < .05) for pigs fed the reagent-grade ZnSO4. Serum, liver, and kidney Zn concentrations were lower (P < .05) for pigs fed the ZnO diet after wk 2 than for pigs fed the ZnSO4 diets, but no differences (P > .10) were observed at the end of wk 4. In summary, performance was not enhanced by feeding pharmacological levels of zinc after weaning, although serum and tissue Zn concentrations were increased. When compared with the bioavailability of Zn in ZnSO4, the bioavailability of Zn was lowest for ZnO and intermediate for Zn-lysine and Zn-methionine.

Three trials were conducted with recently weaned pigs (n = 198) to determine the effects of feeding different types of clay in conjunction with aflatoxin-contaminated diets. In Trial 1, pigs (n = 54; trial length 4 wk) were assigned to either an uncontaminated treatment (NC), 800 ppb of aflatoxin from contaminated corn (AC), or AC with one of four clays. In Trial 2 (n = 81; trial length 5 wk), pigs were assigned to NC, AC (500 ppb of aflatoxin from rice starch), or AC with one of seven types of clay. In both trials, pigs fed AC had decreased ADG and gain:feed ratios (P < .05) compared with controls. The clays differed in their ability to produce gains similar to those of controls. The clays did reduce changes in the serum measurements normally affected by aflatoxin, including albumin, total protein, gamma glutamyltransferase (GGT), and alkaline phosphatase (ALP) levels, in a manner similar to their effect on ADG. In Trial 3, pigs (n = 63) were assigned to one of seven diets for 4 wk: NC, AC (800 ppb of aflatoxin) with no clay, AC with one of four levels of a treated Ca bentonite (.25, .5, 1, and 2%), or AC and .5% hydrated sodium calcium aluminosilicate. The addition of treated Ca bentonite to AC improved ADG (P < .05) and ADFI (P < .01) linearly. Gain:feed ratios were not affected by treatments. The inclusion of treated Ca bentonite to the AC diet linearly decreased aspartate aminotransferase (AST) levels and quadratically decreased ALP and GGT levels (P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Ninety-six crossbred weanling pigs (36 d of age, initial weight of 8.8 kg) were used in a three-phase study to determine the effects of feeding an aflatoxin-contaminated corn (AC) diet (922 ppb of aflatoxin B1) with and without sodium bentonite (clay) on performance, liver function, and mineral metabolism. In the nursery phase, control corn (NC) or AC was fed in corn-soybean meal diets with and without 1% clay for 6 wk. Compared with NC, AC decreased ADFI and ADG (P < .01) and increased serum activities of gamma-glutamyltransferase (P < .01) and alkaline phosphatase (P < .05). In the growing phase, 48 pigs from the nursery phase were fed NC but continued on their respective clay treatments for 5 wk. Pigs previously fed AC had higher (P < .01) ADFI and lower (P < .05) gain/feed, serum Ca, K, and glucose; ADG, other serum values, and liver minerals were not affected by treatments. In the metabolism phase, 24 barrows from the nursery phase were continued on the same corn and clay treatments for two 4-d total collections of urine and feces. Feeding AC increased (P < .05) P and Na absorption. The addition of clay lowered Mg and Na absorption (P < .01) for both AC and NC. Significant interactions for many minerals indicated that the effects on mineral metabolism were more pronounced when AC was fed. Serum and liver mineral concentrations were generally unaffected by the treatments in all phases. Feeding clay with AC results in partial restoration of performance and liver function without greatly influencing mineral metabolism.

We conducted two trials (n = 144 and 96) to evaluate the response of feeding either ZnSO4 x H2O or a zinc-lysine complex (ZnLys) in combination with various lysine levels on growth performance, liver, kidney, and 10th rib Zn concentration, serum Zn humoral immune response and absorption of Zn (chromic oxide method) of young pigs. The following treatments were started after a 7-d postweaning adjustment during which all pigs were fed a common diet adequate in zinc. Diets were as follows: 1) basal 1 (B1), .8% dietary lysine without added Zn (basal contained 32 ppm Zn); 2) B1 plus 100 ppm Zn from ZnSO4; 3) B1 plus 100 ppm Zn from ZnLys, 4) basal 2 (B2), 1.1% lysine without added Zn; 5) B2 plus 100 ppm Zn from ZnSO4; 6) B2 plus 100 ppm Zn from ZnLys. In Trial 1 only, 100 ppm Zn from ZnSO4 (diet 7) or ZnLys (diet 8) was added to a .95% lysine basal diet. The basal 20% CP diet contained 9.0% corn gluten meal to lower the total lysine level. Within lysine level, all diets were made isolysinic by using crystalline lysine. Zinc sulfate, ZnLys, or lysine replaced dextrose in the basal diet. After 4 wk on test, one barrow in each pen was killed; liver, kidney, left 10th rib, and contents of the stomach, small intestine, and lower colon were removed for Zn analyses. Performance (ADG and ADFI) was only improved (P < .05) in one of the two trials when either zinc source was added to the basal diets, but performance was higher (P < .01) for pigs fed 1.1% lysine diets compared with .8% lysine diets in both trials. Serum Zn concentrations were lower (P < .001) for pigs fed both dietary lysine basal diets without added Zn. The humoral response to sheep red blood cells and ovalbumin was not influenced (P > .20) by lysine level, or Zn level and source. Pigs fed diets without added Zn had lower (P < .001) liver, kidney, and rib Zn concentrations than pigs fed diets with added Zn regardless of Zn source. Dietary lysine did not influence liver Zn, but kidney (P < .01) and rib (P < .001) Zn concentrations were lower for pigs fed the higher lysine level. Digestibility coefficients of Zn were lower in the stomach for pigs fed diets without added Zn, similar among Zn levels and sources in the small intestine, and higher in the lower colon for pigs fed the basal diets without added Zn. Lysine level and Zn source did not influence Zn absorption. The ZnSO4 and a zinc lysine complex seemed to be equally effective in promoting growth performance, zinc absorption, and tissue stores of young pigs when diets contained deficient, adequate, or slightly more than adequate levels of lysine.