Effect of phytase supplementation to a high- and a low-phytate diet for growing pigs on the utilization of phosphorus and calcium

Sheng Fa Liao, Willem C. Sauer, John K. Htoo, Miguel Cervantes, Arie Kies, Alfonso Araiza and Adriana Morales

Sheng Fa Liao. Ph.D. in Animal Nutrition, University of Alberta, Canada. Research Associate, University of Kentucky, USA. e-mail: Shengfa.Liao@uky.edu

Willem C. Sauer. Ph.D. in Animal Nutrition. Emeritus Professor, University of Alberta, Canada. Professor Universidad Autónoma de Baja California (UABC), México. e-mail: willem.sauer@afhe.ualberta.c

John K. Htoo. Ph.D. in Non Ruminant Nutrition. Research Associate, University of Alberta, Canada.

Miguel Cervantes. Zootechnical Engineer. Ph.D. in Non-Ruminant Nutrition, University of Kentucky, USA. Professor, UABC, Mexico. Address: Lago Reindeer #933, Jardines del Lago, Mexicali, BC, México CP 21330. e-mail: miguel_cervantes@uabc.mx

Arie Kies. MSc. in Non Ruminant Nutrition. DSM Food Specialties, Delft, The Netherlands.

Alfonso Araiza. Doctor en Ciencias Agropecuarias, UABC. Professor, UABC, Mexico.

Adriana Morales. Ph.D. in Animal Science, Universidad Nacional Autónoma de México. Professor, UABC, Mexico.

SUMMARY

The effect on the utilization of P and Ca of phytase supplementation to a high- and low-phytate diet for growing pigs fitted with a simple T-cannula at the distal ileum, was determined. Eight barrows, 40.6 ±1.7kg BW, were assigned to four dietary treatments according to a repeated 4×4 Latin square design (n=8). Diets were: 1) a high-phytate diet containing 20% rice bran, a rich source of phytate-P; 2) diet 1 supplemented with 2000 phytase units (FTU) per kg; 3) a low-phytate diet containing 2% rice bran; and 4) diet 3 but supplemented with 2000 FTU per kg. Other major diet ingredients were barley, wheat, soybean meal and canola meal, and chromic oxide was added as an inert marker. For high- and low-phytate diets the contents were, respectively, 0.77 and 0.51% total P, 0.48 and 0.22% phytate-P and 1.30 and 0.86% Ca, while available P contents in all diets were similar (0.23%). Feces and urine collections started at 08:00 on day 8 of each 14-day experimental period and continued for 96h. Ileal digesta were collected from 08:00 to 20:00 on days 12-14. The diets were fed at 2.4×ME maintenance requirement according to 1998 NRC standards. Meal allowances of equal amounts were offered twice daily at 08:00 and 20:00. Phytase supplementation improved (P<0.05) the apparent total tract digestibilities and the amount of P and Ca retained. The improvement in P utilization was independent (P>0.10) of diet phytate-P. In the large intestine net absorption of P (P<0.05) occurred for all diets, while that of Ca (P<0.05) only when pigs were fed the non-supplemented low-phytate diet.

Efecto de la adición de fitasa a dietas altas y bajas en fitatos en el uso de fósforo y calcio para cerdos en crecimiento

RESUMEN

Se determinó el efecto de la adición de fitasa a dietas altas y bajas en fitatos en la utilización de P y Ca por cerdos en crecimiento adaptados con una cánula simple tipo T en íleon distal. Se asignaron ocho cerdos, 40,6 ±1,7kg peso corporal, a cuatro dietas de acuerdo con un diseño en Cuadro latino repetido 4 x 4 (n=8). Las dietas fueron las siguientes: 1) dieta alta en fitatos con 20% de salvado de arroz, fuente rica en P-fitato; 2) dieta 1 pero adicionada con 2000 unidades fitasa (FTU) por kg; 3) dieta baja en fitatos con 2% de salvado de arroz; y 4) dieta 3 pero adicionada con 2000 FTU por kg. Otros ingredientes mayores en la dieta fueron cebada, trigo, pasta de soya y pasta de canola; se añadió óxido crómico como marcador inerte. La composición de las dietas altas y bajas en fitatos fue la siguiente: P-total, 0,77 y 0,58%; P-fitatos, 0,48 y 0,22%; y Ca, 1,30 y 0,86%, respectivamente; el contenido de P disponible en todas las dietas fue similar (0,23%). La colecta de heces y orina inició a las 08:00, en el día 8 de cada periodo experimental de 14 d, y continuó por 96 h. El contenido ileal se colectó de 08:00 a 20:00 en los días 12-14. Las dietas se ofrecieron a razón de 2.4x los requerimientos de EM para mantenimiento, de acuerdo con los estándares 1998 del NRC. El alimento se ofreció dos veces al día, en cantidades iguales, a las 08:00 y 20:00. La adición de fitasa mejoró (P<0,05) la digestibilidad aparente en tracto total y la cantidad retenida de Ca y P. La mejora en la utilización del P fue independiente (P>0,10) del contenido de P-fitato en la dieta. Para todas las dietas, se observó absorción neta de P en el intestino grueso; sin embargo, la absorción neta de Ca se observó solo cuando los cerdos se alimentaron con la dieta baja en fitatos no adicionada con fitasa.

Efeito da adição de fitase a dietas altas e baixas em fitatos na utilização de fósforo e cálcio por suínos em crescimento

RESUMO

Determinou-se o efeito da adição de fitase a dietas altas e baixas em fitatos na utilização de P e Ca por suínos em crescimento adaptados com uma cânula simples tipo T em íleo distal. Designaram-se oito suínos, 40,6 ±1,7kg peso corporal, a quatro dietas de acordo com um desenho em Quadro latino repetido 4 x 4 (n=8). As dietas foram as seguintes: 1) dieta alta em fitatos com 20% de farelo de arroz, fonte rica em P-fitato; 2) dieta 1 mas adicionada com 2000 unidades fitase (FTU) por kg; 3) dieta baixa em fitatos com 2% de farelo de arroz; e 4) dieta 3 mas adicionada com 2000 FTU por kg. Outros ingredientes maiores na dieta foram cevada, trigo, pasta de soja e pasta de canola; acrescentou-se óxido crômico como marcador inerte. A composição das dietas altas e baixas em fitatos foi a seguinte: P-total, 0,77% e 0,58%; P-fitatos, 0,48% e 0,22%; e Ca, 1,30% e 0,86%, respectivamente; o conteúdo de P disponível em todas as dietas foi similar (0,23%). A coleta de fezes e urina iniciou-se ás 8 h, no dia 8 de cada período experimental de 14 d, e continuou por 96 h. O conteúdo ileal foi coletado das 8 h às 20 h nos dias 12-14. As dietas foram oferecidas à razão de 2,4x os requerimentos de EM para manutenção, de acordo com os estandards 1998 do NRC. O alimento foi oferecido duas vezes ao dia, em quantidades iguais, ás 8 h e 20 h. A adição de fitase melhorou (P<0,05) a digestibilidade aparente em trato total e a quantidade retida de Ca e P. A melhora na utilização do P foi independente (P>0,10) do conteúdo de P-fitato na dieta. Para todas as dietas, se observou absorção neta de P no intestino grosso; no entanto, a absorção neta de Ca se observou somente quando os suínos se alimentaram com a dieta baixa em fitatos não adicionada com fitase.

KEY WORDS / Calcium / Digestibility / Growing Pigs / Phosphorus / Phytase / Utilization /

Received: 05/08/2006. Modified: 01/23/2007. Accepted: 01/26/2007

Introduction

Feed ingredients of plant origin may contain 0.7-3.5% phytates in the form of poorly soluble Ca-Mg, K-Mg or monoferric salts of phytic acid (Maga, 1982; Suttle, 1983). Swine and poultry have a very limited ability to utilize P contained in phytates. They lack the enzyme phytase, necessary for hydrolysis of phytate. The very limited ability poses nutritional and environmental problems. Growing concerns of environmental P pollution from manure have been globally expressed (Liao et al., 2006).

Previous studies have shown that supplementation of phytase to swine diets can improve the utilization of P from phytate by pigs, and therefore alleviate the negative impact of phytate-P to the environment (Simons et al., 1990; Cromwell et al., 1993; Lei et al., 1993a, b). In light of current knowledge, however, it still does not seem possible to exceed P bio-availabilities of 60 to 70% in feed ingredients of plant origin, even if phytase is supplemented at a very high rate (Liao et al., 2002).

It was hypothesized that the magnitude of improvement in the utilization of P upon phytase supplementation is dependent on the initial phytate content and intrinsic phytase activity in the diet. In other words, a relatively larger improvement would be expected when the dietary phytate content is high and the intrinsic phytase activity is low and vice versa. This hypothesis was tested with two model diets, designed to be relatively high and low in the content of phytate. A further objective was to determine the effect of phytase supplementation on the utilization of Ca. This has been investigated in only a few studies and the results were not always consistent (Adeola, 1995; Kemme et al., 1999; Traylor et al., 2001). The pigs were also fitted with a simple T-cannula at the distal ileum in order to determine the role of the large intestine in the utilization of P and Ca.

Experimental Procedues

Dietary treatments

Two basal diets were formulated to contain a high and a low concentration of phytate-P (Table I). The high-phytate diet contained 20% rice bran, which is a rich source of phytate-P and a poor source of intrinsic phytase (Liao et al., 2002). The low-phytate diet contained only 2% rice bran and 15% corn starch. To each basal diet, Aspergillus niger phytase (Natuphos^Ò, DSM Food Specialties, Delft, The Netherlands) was supplemented at a rate of 2000 phytase units (FTU) per kg diet to formulate two more experimental diets. One FTU is defined as the quantity of phytase that liberates 1mmol of orthophosphate per min from 5.1mM Na-phytate at pH 5.5 and 37°C (Engelen et al., 2001). The diets were supplemented with inorganic P to meet the National Research Council (NRC, 1998) standard for available P, which is 0.23% for growing pigs. Canola oil was included in the diets to increase the content of metabolisable energy (ME) according to NRC (1998) standards. Vitamins, minerals and L-lysine-HCl were supplemented to fulfill the NRC (1998) standards. Chromic oxide was included in the diet at a rate of 0.25% as the digestibility indicator.

Before surgery and during the recuperation period, the pigs were fed ad libitum an 18% CP grower diet. Water was freely available from a low-pressure drinking nipple. The diets were fed in mash form.

Animal trial procedures

Eight Genex F₂ barrows (Large white´Landrace) with average initial BW of 25.3 ±1.7kg, were obtained from the University of Alberta Swine Research and Technology Center. The barrows were housed individually in stainless steel metabolic crates (85´140´65cm; height-length-width) in a barn where the temperature was maintained at 20-22°C. Following a 14-day period of adjustment to the metabolic crates, each barrow was fitted with a simple T-cannula at the distal ileum, about 5cm anterior to the ileo-cecal sphincter. The preparation of the cannulas was previously described by Sauer et al. (1983) and modified by De Lange et al. (1989). The surgical procedure was adapted from that described by Sauer et al. (1983). A detailed description of pre- and post-operative care of animals was previously given by Li et al. (1993).

Following a 7 days recuperation period after surgery, the barrows were fed the four experimental diets according to a repeated 4´4 Latin square design (n= 8). The average BW of the pigs was 40.6 ±1.7kg at the start of the first experimental period. Each of the four experimental periods comprised 14 days. The diets were fed to the pigs at a rate of 2.4 times the maintenance requirement for ME (106kcal/BW_kg^0.75) based on the average BW of the pigs which was determined at the initiation of each experimental period. The meal allowances were offered twice daily at 08:00 and 20:00, equal amounts each meal. Water was added to the meal at a ratio of 2.5:1 (wt/wt) and there was no access to water between meals.

The experimental proposal, surgical procedures, and procedures for use, care and treatment of the pigs were reviewed and approved by the Faculty of Agriculture, Forestry and Home Economics Animal Care Committee of the University of Alberta, Canada, in accordance with the guidelines of CCAC (1993).

Sample collection and chemical analysis

Samples of the feed ingredients were taken after the ingredients were ground through a 2mm mesh screen. Samples of the diets were taken during the time the meal allowances were prepared. The collections of feces and urine were initiated at 08:00 on day 8 of each experimental period and continued for 96 consecutive hours. Feces were frozen at -28°C immediately after collection. Urine, collected through glass wool, was measured volumetrically and stored at -4°C immediately. At the end of each experimental period, urine was pooled for each pig. During pooling the urine was filtered through triple layers of medical gauze. Then, an aliquot of 25% was taken and frozen at -28°C. Ileal digesta were collected into soft plastic tubes (length= 20 cm; i.d.= 4cm) for 36h, from 08:00 to 20:00 on days 12, 13, and 14. Prior to collection, 8ml of a 10% (v/v) formic acid solution was placed into each tube. The tube was attached to the barrel of the cannula with a rubber band, and replaced as soon as it was nearly filled with digesta. Digesta were frozen at -28°C immediately after collection. Detailed procedures for collection of ileal digesta were previously described by Li et al. (1993).

Prior to analysis, feces as well as digesta were pooled for each pig in each experimental period. Feces were dried in a forced-draft oven at 60°C until constant weight, and digesta were freeze-dried. The dried samples of feces and digesta, and samples of ingredients and diets were ground through a 0.5mm mesh screen in a Thomas-Wiley Laboratory Mill (Arther H. Thomas Co., Philadelphia, PA, USA). Urine samples were filtered through Whatman #2 filter paper and then dried in a forced-draft oven prior to analysis.

Dry matter was measured according to AOAC (2000) Method 930.15. Ash was measured according to AOAC (2000) Method 942.05. Gross energy was determined with an AC-300 Leco Automatic Calorimeter (Leco^Ò Corporation, St. Joseph, MI, USA). Crude protein (N´6.25) was measured with a Leco FP-428 Nitrogen Determinator. The NDF contents of the diets were determined by the method of Goering and Van Soest (1970). The P contents were determined photometrically by the molybdovanadate procedure according to AOAC (2000) Method 965.17. The phytate-P contents in the basal diets were analyzed according to the procedures described by Haug and Lantzsch (1983). Ca was analyzed with an atomic absorption spectrophotometric procedure according to AOAC (2000) Method 968.08. With this method, lanthanum chloride was included at the final dilution step providing 1% (g/ml) lanthanum to minimize interference from other minerals. The intrinsic phytase activities in the diets were analyzed with a colorimetric enzymatic procedure (Engelen et al., 1994, 2001). Chromic oxide was determined with a spectrophotometric procedure according to Fenton and Fenton (1979). Analyses of ingredients and diets were carried out in triplicate; analyses of digesta, urine and feces in duplicate.

Calculations and statistical analysis

The apparent ileal digestibility (AID) and the apparent total tract digestibility (ATTD) and balance values of P and Ca were determined. The digestibility values were calculated as

where D_D: AID or ATTD of P or Ca in the assay diet (%), A_F: concentration of P and Ca in ileal digesta or feces (%), I_D: chromic oxide concentration in the assay diet (%), A_D: concentration of P or Ca in the assay diet (%), I_F: chromic oxide concentration in ileal digesta or feces (%). The total amount of P and Ca in feces was estimated based on their ATTD and P and Ca intake. Feces trampled on or contaminated with urine or water were discarded.

The digestibility and balance values were subjected to statistical analysis by using the General Linear Model (GLM) Procedure of SAS^Ò (1990), based on the linear model

Y_ijk = m + T_i + P_j + A_k + e_ijk

where Y_ijk: digestibility or balance value; m: overall mean of the digestibility or balance values; T_i: fixed effect of dietary treatments and i = 1, 2, 3, 4; P_j: random effect of experiment periods and j= 1, 2, 3, 4; A_k: random effect of animals and k= 1, 2, 3, 4, 5, 6, 7, 8; e_ijk: residual experimental error with N (0, s²). The data were analyzed as a 2×2 factorial. The effects of phytate content, phytase supplementation, and the interaction between phytate and phytase were tested. The magnitudes of changes in each parameter upon phytase supplementation to the high- and low-phytate diets were compared with the paired t-test. The differences between the ileal and total tract absorptions, and between the AID and ATTD of P and Ca were also compared with the paired t-test. Probability levels of P£0.05 and 0.05<P£0.10 were defined as significant differences and tendencies, respectively.

Results

Diet analysis

The chemical composition of the experimental diets are presented in Table II. As was expected, since rice bran has a relatively high content of P, neutral detergent fiber (NDF) and ash (Kaufmann, 2003), the contents of P, NDF, and ash were higher in the high- than in the low-phytate diets. As was intended, the content of phytate P was higher in the high- (0.48%) than in the low-phytate diet (0.22%). The analyzed values for the contents of P in the diets were in the same range of values calculated, based on NRC (1998). The analyzed values for Ca were considerably higher than the calculated values based on NRC (1998).

Animals

All pigs remained healthy throughout the experiment and usually consumed their meal allowances within 30min after feeding. The average BW of the pigs were 40.6, 44.4, 53.1, and 60.8kg at the beginning of periods 1, 2, 3, and 4, respectively. The average pig BW was 69.8kg at the conclusion of the experiment. The ADG of the pigs during the experiment was 520g/d. Postmortem examinations conducted at the conclusion of the experiment revealed no intestinal adhesions or any other abnormalities.

Phosphorus balance study

The ileal and fecal outputs of P were lower (P<0.001) in the low- than in the high-phytate diets (Table III). The amount of P absorbed up to the distal ileum was higher (P=0.031) in the low- than in the high-phytate diets, but there were no differences (P=0.394) in the total tract absorption of P between the high- and low-phytate diets. The AID and ATTD of P were higher (P<0.001) in the low- than in the high-phytate diet. However, there was no effect of phytate content on the urinary output of P (P=0.916) and the total amount of P retained (P=0.405).

Phytase supplementation decreased (P<0.001) the ileal and the fecal output of P, and increased (P<0.001) the ileal and total tract absorption, and ATTD of P (Table III). Phytase supplementation also increased (P=0.035) the urinary output of P. The urinary output of P is very small compared to the fecal output. Phytase supplementation increased (P<0.001) the amount of P retained.

These studies indicate that there is net absorption of P in the large intestine (Table V). The total tract absorption of P was higher than the ileal absorption in pigs fed the non- phytase-supplemented (P=0.001) and phytase-supplemented (P=0.049) high-phytate diets. Similarly, the total tract absorption of P was higher than the ileal absorption in pigs fed the non- (P=0.015) and phytase-supplemented (P=0.005) low-phytate diets. Consequently, there were differences between the AID and ATTD of P. The ATTD were higher than the AID of P in pigs fed the high-phytate, non- (P=0.001) and phytase-supplemented (P=0.042) diets, and the low-phytate, non- (P=0.013) and phytase-supplemented (P=0.008) diets.

Calcium balance study

The ileal and fecal outputs of Ca were lower (P<0.001) in the low- than in the high-phytate diets (Table IV). There was an interaction in the ileal absorption (P=0.024) and ATTD (P=0.012) of Ca between phytate content and phytase supplementation to the diets. The ATTD of Ca was higher (P<0.001) in the low- than in the high-phytate diets. There were no differences (P>0.208), however, in the amount of Ca absorbed between total tract and up to the distal ileum. There was no effect of phytate content on the urinary output (P=0.195) and on the amount of Ca retained (P=0.327).

Phytase supplementation did not affect the ileal (P=0.453) and fecal (P=0.164) outputs of Ca (Table IV). The ATTD of Ca increased (P=0.018) upon phytase supplementation to the diets. Phytase supplementation tended to increase (P=0.087) the total tract absorption of Ca. Phytase supplementation decreased (P<0.001) the urinary output of Ca. The urinary output is very small compared to the fecal output. The amount of Ca retained was increased (P=0.015) with phytase supplementation.

The paired t-test showed that the ATTD of Ca was higher (P=0.006) than the AID only in pigs fed the non-supplemented low-phytate diet (Table V). Also, there was net absorption of Ca (P=0.009) in the large intestine only when the non-supplemented low-phytate diet was fed. There were no differences (P>0.115) between the AID and the ATTD of Ca in pigs fed the other diets. The total tract absorption of Ca tended to be higher (P=0.090) than the absorption up to the distal ileum in pigs fed the non-supplemented high-phytate diet. The total tract absorption of Ca was not (P>0.179) different from the absorption up to the distal ileum in pigs fed the phytase supplemented high- or low-phytate diets.

Discussion

Commercial preparations of phytase were developed to increase the bioavailability of P from phytate in feedstuffs of plant origin for non-ruminants, in order to reduce the need for supplementation of inorganic P to diets and to decrease the output of P in manure to alleviate P pollution in the environment. Many studies with pigs have shown that supplementation of phytase can achieve these objectives (Simons et al., 1990; Cromwell et al., 1993; Kemme et al., 1999). Although the recommended rate of phytase supplementation for growing pigs is 500FTU/kg diet, a maximum response can be achieved at a higher rate (Jongbloed et al., 2000). In this study, phytase was supplemented at a rate of 2000FTU/kg diet with the purpose of obtaining a maximum response.

The supplementation of phytase to the high- and the low-phytate diets improved the ATTD of P by 10.4 and 19.6 percentage units (pu), respectively. These results are in agreement with most studies in which phytase was supplemented to diets containing feed ingredients of plant origin as reviewed by Liao et al. (2002). However, the magnitude of improvements in the ATTD of P were smaller in this than other studies reported in the literature, which ranged from 20 to 30pu. The smaller improvements are the result of the relatively high concentrations of P in the diets (0.51-0.77%) as inorganic P was supplemented (Tables I and II). Lei et al. (1993a) reported that phytase supplementation to a corn-soybean meal diet low in total P (0.32%) improved the ATTD of P from 46.4 to 69.0%. At present time, it still does not seem possible to exceed P availabilities of 60-70% in feed ingredients of plant origin even if phytase is supplemented at a very high rate (Liao et al., 2002). One of the reasons is the low affinity of phytase for releasing the phosphate group from position 2 of the phytate molecule (Misset, 2003).

Liao et al. (2002) hypothesized that the magnitude of improvement in the utilization of P upon phytase supplementation is dependent on the initial phytate content and intrinsic phytase activity in the diet. The higher the phytate content and the lower the intrinsic phytase activity, the higher the magnitude of improvement upon phytase supplementation and vice versa. Sands (2002) reported an improvement in the ATTD of P by 16.2pu when phytase was supplemented to a low-phytate diet (0.22%) and a larger improvement of 22.7pu when phytase was supplemented to a high-phytate diet (0.39%). However, in this study, the magnitude of increase in the ATTD of P upon phytase supplementation to the high-phytate diet (11.4pu) was less than when phytase was supplemented to the low-phytate diet (19.6pu).

As shown in Table III, there were no interactions between the phytate content and phytase supplementation level, in the increases of the amount of P absorbed and retained. The values for the increases in the amount of P absorbed from the high- and low-phytate diets upon phytase supplementation were close, 1.17 vs 1.33g/d, respectively. Similarly, the increases in the amount of P retained from the high- and low-phytate diets upon phytase supplementation were also very similar, 1.16 vs 1.32g/d, respectively. Furthermore, the values for the amount of P absorbed and retained are nearly identical, as only small amounts of P are excreted in urine.

The supplementation of phytase tended to increase the amount of Ca that was absorbed and increased the amount of Ca that was retained. These results are somewhat surprising considering the relatively high dietary contents of Ca (0.83-1.31%; Table II). The higher dietary content of Ca likely results from additional CaCO₃ in rice bran. For the production of rice bran, CaCO₃ is usually used in the polishing step to remove the germ and remnants of the bran which is accomplished through abrasive action. Also, since the supplementation of phytase increases P retention, more bone tissue can be synthesized and, as a consequence, more Ca is retained.

Supplementation of phytase to the high-phytate and the low-phytate diet increased the ATTD of Ca by 1.54 and 6.92pu, respectively. These results are in agreement with those reported by Jongbloed et al. (1993) and in a previous study by Liao et al. (2006). They reported that as the dietary content of Ca increases there is a smaller increase in the ATTD of Ca in response to phytase supplementation. The Ca content in the high- and low-phytate diets were 1.31 and 0.85%, respectively. Furthermore, with the exception of the AID and the ileal absorption of Ca, there were no interactions for the other parameters between phytase supplementation level and phytate content of the diets. The magnitudes of increase in the ATTD, the total tract absorption, and the retention of Ca were not significantly different between the pigs fed the high- and the low-phytate diets. Furthermore, the values for the amount of Ca absorbed and retained are very close, as only small amounts of Ca were excreted in urine.

As was pointed out by Fan and Sauer (2002), a controversial topic is the role of the large intestine in the digestion and absorption of P. For three of eight diets they showed significant differences between the AID and ATTD of P. There was a significant net absorption of P in the large intestine of pigs fed both the non- and supplemented low- and high-phytate diets (Table V). For reasons unclear, there was a significant net absorption of Ca in the large intestine of pigs only when these were fed the non-supplemented low-phytate diet.

Conclusion

The supplementation of phytase improved the ATTD and the amount (g/d) of P and Ca retained. The magnitude of improvements in the absorption, ATTD and retention of P was independent of the phytate-P content of the diet. Based on comparisons between ileal and total tract absorption and between AID and ATTD values, there was a significant net absorption of P in the large intestine.

ACKNOWLEDGEMENTS

The authors acknowledge the financial support provided by DSM Food Specialties, Delft, The Netherlands; the Alberta Livestock Industry Development Fund Ltd. and the Alberta Agricultural Research Institute.

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