Growing-finishing performance and carcass characteristics of pigs fed normal and genetically modified low-phytate corn 1,2,3

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1 Growing-finishing performance and carcass characteristics of pigs fed normal and genetically modified low-phytate corn 1,2,3 J. D. Spencer*, G. L. Allee*,4, and T. E. Sauber *Department of Animal Sciences, University of Missouri, Columbia and Optimum Quality Grains, LLC, Urbandale, IA ABSTRACT: A genetically modified corn hybrid homozygous for the lpa1 allele, containing low phytate (LP), and its nearly isogenic equivalent hybrid (normal) were compared in two experiments with growing-finishing swine. In Exp. 1, 210 barrows (27 kg) were allotted to one of six dietary treatments with two corn hybrids (LP and normal) and three P feeding regimens. There were five replicate pens (seven pigs/pen) per treatment. Treatments consisted of diets that were supplemented with P throughout the growing-finishing period (.2% P and.15% supplemental P during growing and finishing phases, respectively) or only during the growing phase (.2% supplemental P) or that were not supplemented with P throughout the growing-finishing period. Performance at the end of the growing phase was based on a 2 2 factorial arrangement of treatments with two corn hybrids and two levels of added P (0 and.2%). This resulted in 10 replicates for the treatments supplemented with.2% P. The finishing phase (73 to 112 kg) was a 2 3 factorial arrangement of treatments with the two types of corn and three regimens of added P during the finishing period. Breaking load (BL) and ash of the fourth metacarpal were evaluated from one pig/pen at the end of the growing phase and from all pigs after slaughter. Pigs fed the LP corn diet without added P had greater body weight gain, feed efficiency, BL, and ash content of the fourth metacarpal than pigs fed the normal corn diet without added P. Performance was similar between pigs fed the LP diet without added P and pigs fed LP and normal corn with added P. In Exp. 2, 1,092 gilts (34 kg body weight) were allotted by weight in a commercial facility to one of three treatments: 1) normal corn/soybean meal diet containing.29% and.22% available P during the growing and finishing phases, respectively; 2) LP corn/ soybean meal diet with the same available P level as Treatment 1; and 3) same as Treatment 2 for 8 wk, then no inorganic P supplementation during the finishing phase. All pigs were slaughtered at approximately 122 kg. There were no significant differences in growingfinishing performance or BL among treatments. However, pigs fed diets containing LP corn possessed carcasses with less backfat and a higher percentage of lean (P <.01). These results confirm that the P in LP corn is available to the pig and suggest that pigs fed diets containing this genetically modified corn will have more desirable carcasses. Key Words: Maize, Performance, Phosphorus, Phytic Acid, Pigs 2000 American Society of Animal Science. All rights reserved. J. Anim. Sci : Introduction Approximately 70% of the P in corn/soybean meal swine diets is unavailable to pigs (NRC, 1998), which results in a large amount of P being excreted into the environment. Sweeten (1992) reported that swine produce over 15 million U.S. tons of manure annually containing 460 thousand tons of P. The increasing concen- tration of animals confined in one location creates a situation in which nutrients such as P can accumulate and create heightened environmental concern. Recently, two nonlethal maize (Zea mays L.) low phytic acid (lpa) mutants have been developed that have 33% (Lpa2) to 66% (Lpa1) less phytic acid P in the kernel than normal corn (Raboy and Gerbasi, 1996). 1 The authors would like to thank Iowa Select Farms, Iowa Falls, IA and C. Hagen and C. Berentschot for assistance in conducting the commercial study (Exp. 2). 2 Contribution from the Missouri Agric. Exp. Sta. Journal Series No. 12,926. Received December 28, Accepted December 7, Partial support for this study was provided by Pioneer Hi-Bred International, Inc., Johnston, IA 50131; Optimum Quality Grains, LLC, Urbandale, IA 50322; Murphy Family Farms, Nevada, MO 64772; the Six State Animal Waste Consortium; Missouri Pork Producers Association; Missouri Farmers Association; and the Missouri Corn Growers Association. 4 Correspondence: 111 Animal Science Research Center (phone: ; fax: ; AlleeG@missouri.edu). 1529

2 1530 Spencer et al. Phenotypically, these corn hybrids are the same as any normal corn, but the seeds contain considerably lower amounts of phytate P in the germ portion of the kernel, with little effect on total kernel P. Two corn hybrids were grown in Iowa during the summer of 1996; one hybrid was homozygous for the lpa1-1 allele, containing low-phytate and the other was the nearly isogenic, normal, equivalent hybrid. Using these two hybrids in concurrent research in our laboratory, we determined the available P content of this LP corn to be approximately.17% for pigs (Spencer et al., 2000). We further determined that P excretion could be reduced 37% in pigs weighing 20 kg if one formulated diets with LP corn and no supplemental P, and we compared them to pigs fed a diet formulated with normal corn and supplemental P from dicalcium phosphate (Spencer et al., 2000). Two studies were conducted to determine the effects of feeding a low-phytate corn on growth performance, bone strength, and carcass characteristics of growingfinishing swine in experimental and commercial production environments. Experiment 1 Materials and Methods Two hundred ten barrows (17 d of age) (Pig Improvement Company C-16 Line 418) were transported to an off-sight segregated early weaning facility and fed common diets containing.9% Ca and.8% P to a body weight of approximately 27 kg. At that time, the barrows were allotted by weight to one of six dietary treatments in a randomized complete block design and taken to an off-site growing-finishing facility. There were five replications (pens) per treatment. Seven pigs were placed in each pen measuring m that allowed for.79 m 2 per pig during the growing phase (27 to 73 kg). All pigs had ad libitum access to one two-hole feeder and nipple waterer. Treatments consisted of diets that were supplemented with P throughout the growingfinishing period (.2% and.15% supplemental P during the growing and finishing phases, respectively) or only during the growing phase (.2% supplemental P) or that were not supplemented with P throughout the growingfinishing period. Performance evaluated at the end of the growing phase (block average of 73 kg) was based on a 2 2 factorial arrangement of treatments with two corn types (low-phytate and normal) and two levels of P addition (.2 and 0%) from dicalcium phosphate. This resulted in 10 replicates for the treatments supplemented with.2% P from dicalcium phosphate and five replicates for treatments not supplemented with inorganic P. Performance evaluated at the end of the entire growing-finishing period (block average of approximately 112 kg) was analyzed as a 2 3 factorial arrangement of treatments with two corn types (low-phytate and normal) and three supplemental P feeding regimens. Table 1. Percentage composition of diets fed during the growing phase (29 to 73 kg) of Exp. 1 a Low-phytate (LP) Item Added P: Ingredient LP corn corn Soybean meal (48% CP) Lysine HCl Limestone Dicalcium phosphate Salt Vitamin premix b Mineral premix c Antibiotic d Calculated composition, % Total P a As-fed basis. All diets were formulated to contain 16% CP,.9% lysine,.6% Ca, and 3,460 kcal ME/kg. b Supplied per kilogram of diet: vitamin A, 8,800 IU; vitamin D 3, 880 IU; vitamin E, 17.6 IU; vitamin K, 3.19 mg; vitamin B 12,.024 mg; riboflavin, 6.6 mg; pantothenic acid, 22.4 mg; niacin, 26.4 mg. c Supplied mg/kg diet: Zn, 165; Fe, 165; Mn, 33; Cu, 16.5; I,.3; Se,.3. d Supplied 55 mg of chlortetetracycline per kilogram of diet. All grower diets were formulated to contain.60% Ca and.90% lysine (Table 1). Formulated levels of Ca and lysine in the finisher diets were.50% and.65%, respectively (Table 2). All diets were mixed and pelleted at the University Feed Mill, where the corn hybrids were stored to ensure preservation of identity. All diets for the growing and finishing phases were mixed and pelleted in order; all the normal corn diets were mixed first, followed by all the low-phytate corn diets. This Table 2. Percentage composition of diets fed during the finishing phase (73 to 112 kg) of Exp. 1 a Low-phytate (LP) Item Added P: Ingredient LP corn corn Soybean meal (48% CP) Lysine HCl Limestone Dicalcium phosphate Salt Vitamin premix b Mineral premix c Antibiotic d Calculated composition, % Total P a As-fed basis. All diets were formulated to contain 13% CP,.65% lysine,.5% Ca, and 3,467 kcal ME/kg. b Supplied per kilogram of diet: vitamin A, 6,600 IU; vitamin D 3, 660 IU; vitamin E, 13.2 IU; vitamin K, 2.39 mg; vitamin B 12,.018 mg; riboflavin, 4.95 mg; pantothenic acid, mg; niacin, 19.8 mg. c Supplied mg/kg diet: Zn, 110; Fe, 110; Mn, 22; Cu, 11; I,.2; Se,.2. d Supplied 55 mg of chlortetetracycline per kilogram of diet.

3 Low-phytate corn for growing-finishing swine 1531 allowed for the mixer and augers to be flushed with the corresponding corn source to ensure that grain identity was maintained and minimize the potential for contamination. All diets were steam-pelleted with a 4.45-cmthick die to make a 4.8-mm pellet before they were individually bagged in 22.7-kg paper bags. At a block average of approximately 73 kg, pigs were switched to finishing diets, and real-time ultrasound was used by a certified technician for evaluation of 10th rib backfat and loin eye area. Additionally, one pig per pen was randomly selected to be slaughtered to obtain the fourth metacarpal for determination of bone breaking load and ash content. All bones were stored, prepared, and analyzed for breaking load and ash determinations as described previously (Spencer et al., 2000). This left six pigs in all pens and allowed.92 m 2 per pig during the finishing phase (73 to 112 kg). When the block averaged approximately 112 kg, all pigs were subjected to real-time ultrasound and slaughtered for extraction of the fourth metacarpal for breaking load and ash determinations. Statistical Analysis The data were analyzed as a randomized couplete block design with a factorial arrangement of treatments. The growing phase was a 2 2 factorial and the finishing phase and entire growing-finishing period was a 2 3 factorial. The pen served as the experimental unit. Analyses was performed using the GLM procedure of SAS (1997) and tested for the main effects and interaction. Carcass measurements of 10th rib backfat and loin eye area were adjusted for live weight by covariance. When interactions of the main effects were found, individual treatment means were separated using the least significant difference test. Experiment 2 One thousand ninety-two gilts (approximately 34 kg body weight) (Pig Improvement Company C22 Line 406) were blocked by weight and randomly allotted in a randomized complete block design to one of three dietary treatments consisting of: 1) normal corn/soybean meal diets formulated to contain.29% available P during the growing phase and.22% available P during the finishing phase; 2) low-phytate corn/soybean meal diet formulated to contain the same available P level as Treatment 1; or 3) low-phytate corn/soybean meal diet formulated to contain the same available P level as Treatments 1 and 2 during the growing period, then no added P from dicalcium phosphate for the remainder of the finishing period (Tables 3 and 4). Available P estimates used in diet formulation for low-phytate and normal corn were.17 and.03%, respectively. These values were obtained from previous research in our laboratory (Spencer et al., 2000) using the same corn hybrids. Additionally, two pens of pigs (one pen of 26 gilts and one pen of 26 mixed-sex pigs) were fed low-phytate corn/ soybean meal diets (.16% available P) with no supplemental P throughout the growing-finishing period for observation. A four-stage growing-finishing phase feeding program (two grower diets followed by two finisher diets) was used, with phase changes occurring every 4 wk. Housing. Pigs were housed in a confinement facility ( m) with double curtain-sided tunnel ventilation and total slats with a scraper manure removal system. Twenty-six pigs were placed in each pen measuring m, allowing for.64 m 2 /pig. All pigs had ad libitum access to one five-hole dry feeder and two nipple waterers. There were 14 replications per treatment, plus the two observational pens of pigs fed lowphytate corn diets without supplemental P. The low-phytate and normal corn diets were ground and mixed at separate feed mills in order to maintain grain identity and minimize the potential for contamination. All diets were sampled and subjected to particle size analysis (ASAE, 1983) to determine the uniformity of particle size between treatments. Diets were fed in the meal form. Daily feedings were recorded, and animal weights were taken every 2 wk for calculation of average daily gain, average daily feed intake, and feed efficiency. After pigs reached an average weight of approximately 122 kg body weight, the animals were transported to a commercial processing facility. At the time of slaughter, two carcasses per pen were randomly selected for extraction of the fourth metacarpal for determination of breaking load by methods described previously (Spencer et al., 2000). For the two observational pens fed low-phytate corn diets with no supplemental P, 15 carcasses/pen were selected for determination of breaking load. Carcass lean percentage was calculated for all carcasses from ultrasonically measured fat, loin depth, and hot carcass weight. The equation used for percentage lean calculations was derived and calculated privately by the commercial processor. After processing, all carcasses were inspected for broken spines or any abnormalities that might be associated with a Pdeficiency. Statistics. Data were analyzed as a randomized complete block design with three treatments. The two observational pens fed low-phytate corn diets with no supplemental P were not included in the statistical analysis. The pen served as the experimental unit. Criteria were tested for treatment effects, with means separated using the least significant difference test. Carcass measurements of backfat depth, loin depth, and percentage lean were adjusted for the covariate of hot carcass weight (SAS, 1997). Experiment 1 Results At the end of the growing phase, a significant (P <.01) corn phosphorus interaction was found for ADG, ADFI, and feed efficiency (Table 5). Pigs fed normal

4 1532 Spencer et al. Table 3. Percentage composition of diets fed during the growing phases (weeks 0 to 8) of Exp. 2 a Week: 0to4 b 4to8 c Item Treatment: Obs. d Obs. Ingredient, % corn Low-phytate corn Soybean meal (48% CP) Fat e L-lysine HCl CuSO Premix Limestone Dicalcium phosphate f Salt Choline chloride Calculated composition, % Crude protein Lysine Calcium Total P Available P g a As-fed basis. b Premix supplied per kilogram of diet: P,.6 mg; Cu, mg; Fe, mg; I,.54 mg; Se,.28 mg; Zn, mg; vitamin A, 6,600 IU; vitamin D, 1,485 IU; vitamin E, 33 IU; vitamin B 1,33 g; vitamin K, 3.3 mg; Mn, 57.8 mg; riboflavin, 4.95 mg; pantothenic acid, 16.5 mg; niacin, 26.4 mg. c Premix supplied per kilogram of diet: P,.2 mg; Cu, 9.98 mg; Fe, mg; I,.4 mg; Se,.3 mg; Zn, 89.8 mg; vitamin A, 5,500 IU; vitamin D, 1,100 IU; vitamin E, 24.2 IU; vitamin B 12, 26.4 g; Mn, 70.3 mg; riboflavin, 4.4 mg; pantothenic acid, 17.6 mg; niacin, 26.4 mg. d Two observational pens of pigs fed low-phytate corn diets with no supplemental inorganic P. e Animal/vegetable blend. f Contained 21% P. g Available P estimates were.17,.03, and.16% for low-phytate corn, normal corn, and soybean meal, respectively. corn diets responded more to added P by improving performance than pigs fed diets formulated with lowphytate corn. Tenth rib backfat (P =.73) and loin eye area (P =.65) were similar for all treatments at the end of the growing phase. An interaction of corn type and P supplementation occurred for bone breaking load (P <.07) and grams of ash in the fourth metacarpal (P <.01). The response in bone characteristics due to supplemental P was greater for pigs fed normal corn than for pigs fed low-phytate corn. Pigs fed low-phytate or normal corn diets supplemented with inorganic P had the highest (P <.05) values and pigs fed normal corn diets with no supplemental P had the lowest values (P <.05) for bone breaking load and ash content (Table 5). At the end of the entire growing-finishing period, there was a significant corn phosphorus interaction (P <.01) for final weight, ADG, ADFI, and feed efficiency (Table 6). No depression in performance occurred when pigs were fed diets formulated with low-phytate corn, with or without P addition. Only pigs fed diets formulated with normal corn and no supplemental P throughout the growing-finishing period had reduced (P <.05) performance. Pigs fed diets containing low-phytate corn tended to have an increased loin eye area compared to pigs fed normal corn diets (main effect of corn hybrid, P <.14). There was no effect of treatment on final backfat (Table 6). Breaking load and ash content of the fourth metacarpal were increased by supplemental P, but the response was greater for pigs fed normal corn than for pigs fed low-phytate corn, resulting in a significant corn phosphorus interaction (P <.01) (Table 7). There was no significant difference in breaking load between pigs fed low-phytate corn with no supplemental P and those fed normal diets with supplemental P throughout the growing-finishing period. As expected, pigs consuming a normal corn diet with P supplementation withdrawn during the finishing phase had metacarpals with a lower (P <.05) breaking load than pigs consuming a diet formulated with normal corn and supplemented with inorganic P throughout the growing-finishing period. Experiment 2 Particle size analysis found that there were differences in geometric mean diameter between treatments due to the separate grinding of low-phytate and normal corn at different feed mills. The normal corn diets had the smallest particle size, with an average of 776 m, and the low-phytate corn diets had larger mean particle sizes of 1,140 m for Treatment 2 and 1,204 m for Treatment 3. The low-phytate corn diets without supplemental inorganic P fed during the growing and finishing periods had a mean particle size of 1,189 m.

5 Low-phytate corn for growing-finishing swine 1533 Table 4. Percentage composition of diets fed during the finishing phases (weeks 8 to 16) of Exp. 2 a Week: 8to12 b 12 to 16 c Item Treatment: Obs. d Obs. Ingredient, % corn Low-phytate corn Soybean meal (48% CP) Fat e L-lysine HCL Premix Limestone Dicalcium phosphate f Salt Choline chloride Calculated composition, % Crude protein Lysine Calcium Total P Available P g a As-fed basis. b Premix supplied per kilogram of diet: P,.2 mg; Cu, 9.98 mg; Fe, mg; I,.4 mg; Se,.3 mg; Zn, 89.8 mg; vitamin A, 5,500 IU; vitamin D, 1,100 IU; vitamin E, 24.2 IU; vitamin B 1, 26.4 g; Mn, 70.3 mg; riboflavin, 4.4 mg; pantothenic acid, 17.6 mg; niacin, 26.4 mg. c Premix supplied per kilogram of diet: P,.16 mg; Cu, 7.98 mg; Fe, 63.9 mg; I,.32 mg; Se,.24 mg; Zn, 71.9 mg; vitamin A, 4,400 IU; vitamin D, 880 IU; vitamin E, 19.4 IU; vitamin B 1, 21.1 g; Mn, 56 mg; riboflavin, 3.5 mg; pantothenic acid, 14 mg; niacin, 21.1 mg. d Two observational pens of pigs fed low-phytate corn diets with no supplemental inorganic P. e Animal/vegetable blend. f Contained 21% P. g Available P estimates were.17,.03, and.16% for low-phytate corn, normal corn, and soybean meal, respectively. Previous research has shown an improvement in feed efficiency when particle size of grain is reduced (Mahan et al., 1966; Lawrence, 1983). Wondra et al. (1995) reported an improvement of 10.3% in feed efficiency when corn particle size was reduced from 1,000 to 400 m in pelleted diets for finishing swine. Reviewing data from several experiments, Hancock et al. (1997) suggested that pigs fed corn diets with particle sizes ranging from 1,200 to 400 m will experience a 1.3% improvement in feed efficiency for each 100- m reduction in mean Table 5. Effect of phosphorus addition to low-phytate and normal corn on pig performance and bone and carcass characteristics during the growing phase (27 to 73 kg) of Exp. 1 a Low-phytate (LP) Item Added P, %: CV P-value Final body weight, kg 76.8 g 74.4 f 77.0 g 66.9 e 5.92 <.01 h Avg daily gain, kg.93 g.89 f.93 g.74 e 3.19 <.01 h Avg daily intake, kg 2.28 f 2.21 f 2.29 f 2.04 e 3.73 <.01 h Gain/feed.41 f.40 f.41 f.36 e 2.48 <.01 h Backfat depth, cm b f e h Loin eye area, cm 2b f e h Breaking load, kg force cd 112 g 94 f 107 fg 67 e <.07 h Ash, g cd 5.06 g 4.64 f 4.96 fg 3.44 e 6.94 <.01 h Ash, % cd f e h a Each value is the least squares mean of 10 or 5 pens (7 pigs/pen) containing high lean-growth barrows (PIC C-16 Line 418) for.2 and 0% added P treatments, respectively. b Backfat depth = 10th rib backfat depth; loin eye area = 10th rib loin eye area. Measurements were taken by real-time ultrasound. Values adjusted for covariate of live weight. e Fourth metacarpal. d Values represent treatment least squares mean of five pigs for all treatments. e,f,g Means in the same row without a common superscript differ (P <.05). h Corn phosphorus effect.

6 1534 Spencer et al. Table 6. Effect of phosphorus addition to low-phytate and normal corn diets on performance and carcass characteristics of growing-finishing pigs (27 to 112 kg) in Exp. 1 ab Low-phytate Entire Growing No P Entire Growing No P Item Added P: grow-finish only addition grow-finish only addition SEM P-value Final weight, kg d d d d d 96.6 e 1.32 <.01 f Avg daily gain, kg.88 d.89 d.90 d.87 d.88 d.73 e.014 <.01 f Avg daily intake, kg 2.51 d 2.55 d 2.53 d 2.50 d 2.54 d 2.23 e.032 <.01 f Gain/feed.37 d.36 d.36 d.36 d.36 d.33 e.004 <.01 f Backfat depth, cm c =.88 Loin eye area, cm 2c <.14 g a Phosphorus addition was.2% during the growing phase (27 to 73 kg) and.15% during the finishing phase (73 to 112 kg). b Each value represents the least squares mean of five pens (six pigs/pen) of high lean-growth barrows (PIC C-16 Line 418). c Backfat depth = 10th rib backfat; loin eye area = 10th rib loin eye area. Measurements taken by real-time ultrasound and adjusted by covariate of final weight. d,e Means in the same row without a common superscript differ (P <.05). f Corn phosphorus effect. g Main effect of corn hybrid. particle size. In addition to calculated gain/feed, Table 8 provides gain/feed for the low-phytate corn diets adjusted for differences in mean particle size assuming an improvement in gain/feed of 1.3% for each decrease in particle size of 100 m. There were no differences among treatments for average daily gain or breaking load (Table 8). Gain/feed was decreased (P <.10) for pigs fed low-phytate corn diets, but this was likely due to the larger particle size of the low-phytate corn. Adjusting gain/feed for particle size suggests that no true differences in gain/feed existed among treatments. Pigs fed low-phytate corn diets had less backfat and a higher percentage of carcass lean (P <.01). After processing, inspection of carcasses revealed that only eight carcasses (less than 1% of the total number of carcasses) were found to have broken spines, with no specificity for any particular treatment. No depression in performance, carcass characteristics, or bone strength was observed for the two pens of pigs fed low-phytate corn diets formulated with no supplemental P throughout the growing-finishing period (Table 9). Furthermore, out of 52 carcasses from these two pens, none was found to contain a broken spine or have any visible symptoms of a P deficiency. Discussion These studies demonstrate the marked difference in P availability for pigs between a genetically modified low-phytate corn and its nearly isogenic equivalent normal corn. In Exp. 1, pigs fed low-phytate corn/soybean meal diets with no added P had no depression in growth performance or carcass characteristics. It should, however, be stressed that these animals were all barrows and had a very high feed intake (approximately 2.5 kg/ d for the entire growing-finishing period), which resulted in an intake of approximately 4.25 g of available P per day. This average intake of available P is very close to the recommended level of available P per day proposed by the NRC (1998) for growing pigs from 20 to 120 kg. These intakes are considerably higher than those seen in most commercial production situations, in which pigs are typically raised at a higher density. Also, high lean-growth barrows typically consume approximately 415 g of feed a day more than their gilt littermates (NRC, 1998). Therefore, it is critical to pay special attention to feed intake, especially grams of available P intake, in commercial production systems if one is to formulate diets with low-phytate corn and no Table 7. Effect of phosphorus addition on characteristics of the fourth metacarpal from pigs fed low-phytate and normal corn diets (27 to 112 kg) in Exp. 1 ab Low-phytate Entire Growing No P Entire Growing No P Item Added P: grow-finish only addition grow-finish only addition SEM P-value Breaking load, kg force g fg de ef d 79.4 c 3.72 <.01 h Ash, g 7.4 fg 7.8 g 6.9 de 7.2 ef 6.5 d 4.5 c.169 <.01 h Ash, % 61.2 e 61.1 e 59.3 d 60.1 de 59.0 d 53.5 c.570 <.01 h a Phosphorus addition was.2% during the growing phase (27 to 73 kg) and.15% during the finishing phase (73 to 112 kg). b Each value represents the least squares mean of five pens (six pigs/pen) of high lean-growth barrows (PIC C-16 Line 418). c,d,e,f,g Means in the same row without a common superscript differ (P <.05). h Corn phosphorus effect.

7 Low-phytate corn for growing-finishing swine 1535 Table 8. Growth performance, metacarpal breaking load, and carcass characteristics of pigs fed diets containing low-phytate or normal corn in Exp. 2 a corn Low-phytate corn Low-phytate corn Growing diet available P, %: Item Finishing diet available P, %: SEM Avg daily gain, kg Avg daily intake, kg 2.01 d 2.10 de 2.11 e.04 Gain/feed Unadjusted.36 d.34 e.35 e.01 Adjusted b Breaking load, kg force c Backfat depth, cm 1.72 d 1.65 e 1.59 e.03 Loin depth, cm Lean, % d de e.21 a PIC genetics (C22 Line 406). Twenty-six gilts/pen, 14 pens per treatment. Measurements of backfat depth, loin depth, and percentage lean adjusted for covariate of hot carcass weight. b Adjusted feed efficiency for variation in particle size. c Breaking load of the fourth metacarpal, two carcasses/pen. d,e Means within a row with different superscripts differ significantly (P <.10). supplemental P. From the results in Exp. 1, we further concluded that removing inorganic P supplementation from normal corn/soybean meal diets when pigs weigh 73 kg significantly decreases the bone breaking load, which could lead to potential processing problems such as spinal breaks or further trim loss. If one is to use the method of withdrawing inorganic P sources from diets fed to finishing swine, extreme caution should be paid to possible economic losses at the time of processing due to trim loss and the potential decrease in the overall carcass value. Experiment 2 further showed that in a commercial swine production system, pigs fed low-phytate corn diets formulated on an available P basis show no depression in growth performance or bone characteristics. Table 9. Growth performance, carcass composition, and bone characteristics of observational pens of gilts and mixed-sex pigs fed low-phytate corn diets formulated with no supplemental phosphorus throughout the growingfinishing period a of Exp. 2 Item Gilts Barrows + gilts Growing diet available P, % Finishing diet available P, % Avg daily gain, kg Avg daily intake, kg Gain/feed Unadjusted Adjusted b Backfat depth, cm Loin depth, cm Lean, % Breaking load, kg force c a PIC genetics (C22 Line 406). Twenty-six pigs/pen. Measurements of backfat depth, loin depth, and percentage lean adjusted for covariate of hot carcass weight. b Adjusted feed efficiency for variation in particle size. c Breaking load of the fourth metacarpal, 15 carcasses/pen. Furthermore, even at the higher pig densities and under the commercial production environment of Exp. 2, no depression in performance or bone strength occurred when pigs were fed diets formulated with low-phytate corn and no supplemental P throughout the growingfinishing period. This suggests that it may be possible to feed diets with no supplemental P to growing-finishing swine even under conditions in which feed intake is lower than that observed in Exp. 1. The increased loin eye area and percentage of muscle of pigs fed diets containing low-phytate corn diets in Exp. 1 and 2 may be due to an increase in amino acid availability in the low-phytate corn resulting from less phytate being available for amino acid-phytate complexes. Phytate can have a negative effect on protein utilization by complexing with proteins under acidic conditions (De Rham and Jost, 1979). Even at low or neutral ph, it is thought that phytate can bind with protein and amino acids. Singh and Kridorian (1982) reported that phytate can also bind with trypsin in the gastrointestinal tract, thereby decreasing the digestibility of proteins by making proteases less accessible. The use of exogenous, microbially derived phytase that improves the digestibility of phytate P has also been shown to improve the digestibilities of certain amino acids. Jongbloed et al. (1997) reported that in 45-kg barrows the addition of 800 phytase units/kg significantly increased the apparent ileal digestibility of methionine and arginine. Further trends toward increased apparent ileal digestibility of crude protein, lysine, cystine, tryptophan, histidine, and proline were reported as well. In turkey poults, Yi et al. (1996) reported that levels of 750 phytase units/kg also increased digestibilities of amino acids. However, future experimentation using low-phytate corn in swine and poultry diets is needed to confirm the effects of low-phytate corn on amino acid digestibilities.

8 1536 Implications We conclude that low-phytate corn with reduced levels of inorganic P supplementation can be fed to growing-finishing swine in experimental and commercial conditions with no detrimental effects on pig performance, bone strength, or carcass characteristics. Furthermore, results from Exp. 2 lend validity to our previously determined available P estimates for low-phytate corn of.17%, because these diets were balanced to an equal available P content. These results confirm that P in low-phytate corn is available to the pig and suggest that low-phytate corn-soybean meal diets with no supplemental P may be adequate for growing-finishing swine. Feeding low-phytate corn may also enhance nutrient availabilities, leading to improved carcass merit. Literature Cited ASAE Method of determining and expressing fineness of feed materials by sieving. In: Am. Soc. Agric. Eng. Standard S319. pp 325. Yearbook of Standards, ASAE. De Rham, O., and T. Jost Phytate protein interactions in soybean extracts and low phytate soy protein products. J. Food Sci. 44: Hancock, J. D., K. J. Wondra, S. L. Traylor, and I. Mavromichalis Grinding, mixing, pelleting, and formulation strategies to improve growth performance and decrease cost of gain in pigs. Presented at 58th Minnesota Nutr. Conf. and BASF Tech Symp., Sept , Bloomington, MN. Spencer et al. Jongbloed, A. W., L. dejong, P. A. Kemme, Z. Mroz, and A. K. Kies Nutrition news: Protein and amino acid effects of phytase in swine diets. NN BASF Corp., Mount Olive, NJ. Lawrence, T. L. J The effects of cereal particle size and pelleting on the nutritive value of oat-based diets for the growing pig. Anim. Feed Sci. Technol. 8: Mahan, D. C., R. A. Pickett, T. W. Perry, T. M. Curtin, W. R. Featherson, and W. M. Beeson Influence of various nutritional factors and physical form of feed on esophagogastric ulcers in swine. J. Anim. Sci. 25: NRC Nutrient Requirements of Swine. (10th Ed.) National Academy Press, Washington, DC. Raboy, V., and P. Gerbasi Genetics of myo-inositol phosphate synthesis and accumulation. In: Subcellular Biochemistry: Myo- Inositol Phosphate, Phosphoinositides, and Signal Transduction. pp Plenum Press, New York. SAS Software: Changes and Enhancements through Release SAS Inst. Inc., Cary, NC. Singh, M., and A. D. Kridorian Inhibition of trypsin activity in vitro by phytate. J. Agric. Food Chem. 30: Spencer, J. D., G. L. Allee, and T. E. Sauber Phosphorus bioavailability and digestibility of normal and genetically modified low-phytate corn for pigs. J. Anim. Sci. 78: Sweeten, J. M Livestock and poultry waste management: A national overview. In: J. Blake, J. Donald, and W. Magette (Ed.) National Livestock, Poultry, and Aquaculture Waste Management. pp American Society of Agricultural Engineers, St. Joseph, MI. Wondra, K. J., J. D. Hancock, K. C. Behnke, R. H. Hines, and C. R. Stark Effects of particle size and pelleting on growth performance, nutrient digestibility, and stomach morphology in finishing pigs. J. Anim. Sci. 73: Yi, Z., E. T. Kornegay, and D. M. Denbow Effect of microbial phytase on nitrogen and amino acid digestibility and nitrogen retention of turkey poults fed corn-soybean mean diets. Poult. Sci. 75: