Inclusion of wheat bran in barley-soybean meal diets with different phosphorus levels for growing-finishing pigs I. Effects on nutrient digestibility and mineral balances in finishing pigs Eija Helander, Matti Näsi and Kirsi Partanen Helander, E„ Näsi, M. & Partanen, K. 1994. Inclusion of wheat bran in barley-soy- bean meal diets with different phosphorus levels for growing-finishing pigs. I. Effects on nutrient digestibility and mineral balances in finishing pigs. Agricultural Science in Finland 3: 27-39. (Department of Animal Science, P.O. Box 28, FIN-00014 University of Helsinki, Finland. Present address: Eija Helander, Cultor Ltd, P.O. Box 105,FIN-00241 Helsinki, Finland.) The effect of the intrinsic phytase ofwheat bran (WB) on phytin-phosphorus availabil- ity to pigs on barley-soybean meal diets was measured in a digestibility and balance experiment using a 2x3 factorial arrangement in a 6x5 cyclic change-over design. The factors were WB inclusion (0 or 100 g per kg, later referred to as WB- and WB+, respectively) and three phosphorus (P) levels: high (HP), medium (MP) and low (LP). The inclusion of WB in the diet did not significantly improve dietary P utilization. However, the absorption and retention of P appeared to be slightly improved by WB inclusion in the LP diet. This improvement may be due to WB phytase. The effects of WB on the digestibility and balance of other minerals remained relatively small. The P level, on the other hand, had a greater effect on mineral balances. Ash digestibility was not affected by the treatments. Dry matter and organic matter digestibilities were impaired when WB was included in the diet. Nabsorption of intake was higher (pcO.Ol) on WB+ diets. The retention of N appeared todecrease on HP and MP diets due to WB, but on LP diets no decrease was observed. Regarding the polluting P-emission, the LPWB+ diet appeared to be the most favourable, since the faecal excretion ofP was the lowest and the overall retention coefficient of P was the highest. On the basis of these results, an addition of 100 g WB to the diet in order to improve P utilization does not seem very attractive. Key words: phytin, phytase, availability Introduction More than half of the phosphorus (P) in feedstuffs of plant origin occurs in the form of phytate, which is poorly available to non-ruminants (CROMWELL 1992). Phytic acid readily forms complexes with several minerals, like calcium (Ca) and iron (Fe) (Harris 1955),zinc (Zn) and manganese(Mn) (ref. Erdman 1979) as well as with proteins (Scheuer- mann et al. 1988a), thus reducing their availability to animals. High levels of phytate in the diet can also cause magnesium (Mg) deficiency (Pomer- ANZ 1978). Pig diets are generally supplemented with inorganic P to ensure that the P requirement is satisfied. If the phytate P of plants could be made more available, a reduction in inorganic P supple- mentation of the feeds would be possible, making P-emissions through manure decrease consider- ably. Phytase catalyzes the hydrolysis ofphytic acid to 27 Agricultural Science in Finland 3 (1994) https://www.c-info.fi/en/info/?token=Xzkq_gYT_kjeQpy0.yY5yPajNYdlunznashe_vw.qlqegRGHvBQeVh9mHZVxUvJb9Kebmx9KrxaZjgF_nnJ8YNu_t3oQEco7Kbp2hNQ43ZJxWgsH1bvEnhdgxZEovmpCPcQNv9f4lcAkQC_6O78Ak32a0-WeqH5P7srtR0cY43-g5dLv7ibkKroji7naqpi-vsRjVbGgTt7AMA3nRzdhj33FdawMumB666fqCi5cE_QbWFydhuBfd0gQQNCRqmLQrYg6c_Yu1Hhx7s45K5pS-xHlEHv7SbC4BuMnUMIam5ydAlB4djN_2ijcdzTCrydcZnrzgC8nneeaaNTvjLQXfG0GN90oag inositol and orthophosphate. The intrinsic phytase activity of different plants varies considerably. Wheat is one of the feedstuffs which has a high phytase activity ranging from 300 to 2000 lU/kg (1 IU is 1 pmol P liberated from sodium phytate/min at 37°C) (Pointillart 1988). Most of its phytase appears in the surface layers (Pomeranz 1978). In an experiment by Scheuermann et al. (1988 a), wheat phytase was found to hydrolyze maize phy- tate to the same extent as wheat phytate. Bagheri and Gueguen (1985) have established that the utilization of P improved when an oats-soybean meal diet was supplemented with 200 g of wheat bran (WB) per kg. WB addition also improved the utilization of Mg but decreased thatof Ca and Zn. The present work was undertaken to evaluate whether the intrinsic phytase ofWB could improve the digestibility of phytic P in commercial barley- soybean meal diets enough to serve as a partial or complete replacement for the added inorganic P in the diets ofgrowing-finishing pigs. Material and methods The digestibility and balance assay was conducted with six Large White x Landrace barrows using a 2x3 factorial arrangement in a 6x5 cyclic change- over design. The factors were WB inclusion (0 or 100 g per kg, later referred to as WB- and WB+, respectively) and threeP levels, high (HP), medium (MP) and low (LP) corresponding to 4.33 g(3/3), 2.99 g (2/3) and 1.64 g (1/3) digestible P per feed unit (FT) = 0.7 kg starch equivalent), respectively. Thus, the experiment consisted of six different diets: HPWB-, HPWB+, MPWB-, MPWB+, LPWB- and LPWB+. The nutrient digestibility, ni- trogen (N) balance and the balance of P, calcium (Ca), magnesium (Mg), potassium (K) and zinc (Zn) were determined. The pigs were kept in meta- bolism cages made of galvanized iron, which al- lowed separate quantitative collection offaeces and urine. Each period lasted 10 days; five days of adjustment and five days of collection. The initial weight of the pigs was 70.6 kg (SE 3.57) and the final weight 122.5 kg (SE 5.52). The feeds were pelleted (65°C, 4 mm diameter) barley-soybean meal complete mixtures. The com- position of the experimental diets is shown in Table I. HP diets have been found adequate for pigs with respect to all nutrients (Salo et al. 1990), and the others with respect to all other nutrients except P. The inorganic source of P in the present experi- ment was dicalciumphosphate. The energy content was 0.99 FU/kg in WB- diets and 0.96 FU/kg in WB+ diets. The intention was to give the same Table 1. Composition of the experimental diets, g/kg. Treatment 1 HPWB- HPWB+ MPWB- MPWB+ LPWB- LPWB + Barley 756 668 759 670 764 674 Soybean meal 189 178 188 178 187 178 Wheat bran - 100 - 100 - 100 Molasses 20 20 20 20 20 20 Dicalciumphosphate 16 15 9 8 1 Limestone 7 7 12 12 16 16 Serla Bondex 5 5 5 5 5 5 NaCl 3 3 3 3 3 3 Trace mineral mix 2 2 2 2 2 2 2 Vitamin mix 3 111111 Lysine 111111 HP = high P, MP = medium P, LP = low P, WB- = no wheat bran, WB+ = 100 g wheat bran/kg diet. 2 Supplied per kg diet: 20 mg Fe, 21 mg Mn, 21 mg Cu, 73 mg Zn, 0.2 mg I and 0.1 mg Se. 3 Supplied per kg diet: 5000 IU vitamin A, 800 IU vitamin D, 60 mg vitamin E, 2 mg vitamin K, 2 mg thiamin, 3mg riboflavin, 20 pg vitamin 8, 2 , 50 pg biotin, 10 mg pantothenic acid and 20 mg niacin. 28 Agricultural Science in Finland 3 (1994) amount ofFUs/d to each pig (ranging from 2.6 FU to 3.0 FU/pig/d in periods 1 to 5, respectively) but, in practice, the pigs on WB-diets got 0.16 FU/d more than the other pigs. Just before feeding, the feed was mixed with water (one litre water per kg feed) and afterfeeding the pigs were given water ad libitum. The feeds and faeces were analyzed by standard methods (AOAC 1984). Amino acids were assayed with a Beckman 6300 amino acid analyzer. ICP- AES equipment was used in phytic acid determina- tion (Flaami and Kumpulainen 1991). The sam- ple was first burned by inductively coupled plasma and then the P content of the sample was indirectly measured by atomic emission spectrophotometry. P from feeds, water and faeces was analyzed col- orimetrically after dry ashing by the vanadomolyb- date procedure ofTayssky and Shorr (1953). The other minerals of the feeds, drinking water, faeces and urine were measured with a Perkin-Elmer 5100 PC atomic-absorption spectrophotometer, except K, which was assayed with a Corning 435 flame photometer. Phytase activity was measured as free phosphate from phytate after incubating the sample in a 0.1 M sodium acetate buffer, pH 5.0, at 35°C for 30 min. A phytase unit (U) is defined as the amount of enzyme that liberates 1 pmol of inor- ganic P from sodium-phytate in one minute. Phy- tase activity was measured from the main raw ma- terials and from the complete feeds. The data were subjected to an analysis of vari- ance using the following model (Snedecor and Cochran 1989): Yijk H + Ai + Pj + Tk + eijk where p = overall mean, Ai = the effect ofanimal i, Pj = the effect of period j, Tk = the effect of treat- ment k and eijk = residual error. In analyzing the crude protein digestibility, N intake was used as a covariate. All other results were first corrected by using FU intake as a covari- ate, but because it did not have any significant effect on the digestibility and retention of the nutri- ents, this covariate was omitted. The degrees of freedom for treatment effects were further parti- tioned into single degrees offreedom by the follow- ing orthogonal contrasts: Cl = WB- vs. WB+, C 2 = linear effect of P level, C 3 = quadratic effect of P level, C 4 = interaction Cl x C2, C 5 = interaction Cl x C 3. Results and discussion Chemical analyses The analyzed chemical composition of the experi- mental diets is presented in Table 2. Although the experimental feeds were produced in the normal production line of a big feed factory, not designed for mixing small feed batches, the chemical compo- sition of the diets was relatively close to the target. Only the protein and amino acid contents of the diets were sligtly higher than targeted and, there- fore, the HPWB+ and MPWB+ diets contained more protein per FU than the other diets. The hemi- cellulose content varied from 101 g/kg DM to 130 g/kg DM, naturally being higher on WB+ diets. Table 3 shows the P, Ca and phytase content of the diets and feed ingredients. The P content of barley was 3.5 g/kg DM and two thirds of it was of phytic origin, which is in accordance with the fig- ures reported earlier by PoiNTILLART (1988) and JONGBLOED et al. (1991). In WB, 0.89 of total P was of phytic origin. PoiNTILLART (1988) has re- ported the corresponding figure to be 0.75 for wheat bran and Jongbloed et al. (1991) 0.80 for wheat middlings. According to a review by House- man and de Bruyne (1989), phytate P is located in the aleurone and pericarp layers in monocotyle- dons. Thus, the content of phytate P in wheat bran is highly dependent on the technical process it comes from. The P contents in HPWB- and HPWB+ diets were 8.2 and 8.0 g/kg DM, in MPWB- and MPWB+ diets 6.1 and 6.2 g/kg DM, and in LPWB- and LPWB+ diets 4.4 and 4.9 g/kg DM, respec- tively. The phytic P content of the experimental diets varied from 0.305 to 0.621 in total P, being always higher on WB+ diets. The digestible P con- tent of the diets was calculated by using the deter- mined digestibility coefficients (Table 6). Digest- 29 Agricultural Science in Finland 3 (1994) Table 2. Chemical composition (g/kg DM) and calculated energy content of the experimental diets. Treatment 1 HPWB- HPWB+ MPWB- MPWB+ LPWB- LPWB + Dry matter Ash 897 893 896 891 891 900 61 64 61 62 55 54 Crude protein Crude fat 199 199 204 202 201 196 26 28 21 24 24 30 Crude fibre 53 53 49 55 56 58 Nitrogen free extract Hemicellulose 661 656 665 657 664 662 104 130 101 114 124 128 Cellulose Lysine 54 48 51 49 50 52 10.2 10.1 11.5 10.5 10.7 11.1 Threonine 7.2 7.1 7.4 7.1 7.0 6.8 FUVkg feed 0.99 0.96 0.99 0.96 0.99 0.96 ME MJ/kg feed 12.4 12.0 12.4 12.0 12.4 12.0 HP = high phosphorus (P), MP = medium P, LP = low P, WB- = no wheat bran, WB+ = 100 g wheat bran/kg diet. 2 FU = 0.7 kg starch equivalent. Table 3. Phosphorus, calcium and phytase contents of the experimental diets and feed ingredients (g/kg DM) Treatment 1 HPWB- HPWB + MPWB- MPWB + LPWB- LPWB+ Soybean Barley Wheat meal bran Phosphorus 8.2 8.0 6.1 6.2 4.4 4.9 6.8 3.5 11.3 Phytic acid 9.0 11.0 9.3 10.9 8.8 10.7 14.4 8.2 35.6 P from phytic acid 2.5 3.1 2.6 3.1 2.5 3.0 4.0 2.3 10.0 Phytic P % of total P 0.305 0.388 0.426 0.496 0.560 0.621 0.590 0.657 0.891 Phytase, U/kg < 600 <7OO < 300 < 400 < 300 < 500 n.d. 2 300 2800 Digestible P (measured) 4.2 4.2 2.7 2.5 1.4 1.8 Calcium 9.9 9.7 10.5 10.0 10.4 10.7 Digestible Ca 3.51 3.22 3.66 3.39 3.48 3.77 Ca:P ratio 1.21 1.21 1.72 1.62 2.35 2.20 Ca:dig.P ratio 2.36 2.31 3.89 4.0 7.43 5.94 Dig.Ca:dig.P ratio 0.84 0.77 1.36 1.36 2.49 2.09 HP = high phosphorus (P), MP = medium P, LP = low P, WB- =no wheat bran, WB + = 100 g wheat bran/kg diet. 2 n.d. = not detected. ible P ranged from 4.2 to 1.4 g/kg DM. On a LPWB+ diet, the measured digestible P content was 0.4 g/kg DM (28%) higher than on a LPWB- diet. This difference cannot be explained by the differences in the total P content of the diets, al- though theLPWB+ diet contained 11% more P than the LPWB- diet. The difference may rather be at- tributed to WB phytase. The phytase activity of WB was 2800 U/kg. Pointillart (1988) has measured activities be- tween 600 and 1700 lU/kg for wheat bran. The highest enzyme activities in wheat are found from its surface layers (Pomeranz 1978); thus, the processing technology affects the phytase activity of the end product. The phytase activity of barley was the same as in anotherexperiment by Helander (1993, preliminary results). Soybean meal did not show any phytase activity. COSGROVE and IRVING (1980) have reported phytase activity in soybeans, and Bagheri and Gueguen (1982) have also indi- cated SBM to have some phytase activity. It is likely that the phytase activity in SBM depends on 30 Agricultural Science in Finland 3 (1994) the temperature of the process SBM comes from. There is some inaccuracy in the figures concern- ing the phytase activitity of the diets; e.g., 100 g of WB per kg should have increased the phytase activ- ity of WB+ diets by 280 U/kg. No such increase, however, could be found, which lends support to activity loss during pelleting. Steam pelleting at 80°C reduced the phytase activity in an experiment by Jongbloedand Kemme (1990), and Schwarz and Schöner (1991) reported 15-25 % losses in phytase activity when the temperature of the pellets was 70°C. Since the pelleting temperature in the present trial was lower, this does not explain the smaller-than-expected differences between the treatments. It is probably more a question of an analytical problem: when the phytase activity of the feeds is low, the sensitivity of the analytical method may not be sufficient (Puhakka 1993, personal communication). In any case, the phytase activity was always higher on WB+ diets than on other diets. Digestibilities and balances The average dry matter intake of the pigs was 2526 g (82 g/VT 15 ) on WB- diets and 2435 g (79 g/W0 ' 75 ) on WB+ diets. The difference in daily energy intake was 0.16 FU. The pigs on WB+ diets ate on average 38 g more hemicellulose and 8.6 g more cellulose per day in spite of their lower total feed intake. WB inclusion was found to impair the dry matter digestibility (pcO.OOl) (Table 4). There tended to be an interaction between WB inclusion and P level in organic matter digestibility: the di- gestibility decreased linearly on WB+ diets (p<0.05) when the P level of the diets decreased and tended (p 0.10) NS Cl = WB- vs. WB + , C 2 = P lin, C 3 = P quadr, C 4 = Cl X C2, C 5 = Cl X C3 31 Agricultural Science in Finland 3 (1994) 1 Table 5. Nitrogen balance and protein utilization in pigs fed on the experimental diets. Treatment HP MP LP SHM Statistical significance WB- WB+ WB- WB+ WB- WB + Cl C 2 C 3 C 4 C5 N intake, g/d 80.6 77.7 85.2 78.2 80.7 76.5 0.41 *** NS *** NS ••• N excretion in faeces, g/d 13.1 11.6 12.8 12.6 12.6 12.5 0.26 * NS NS • NS N digested, g/d 67.5 66.1 72.4 65.6 68.0 64.0 0.59 *** NS *** •** -of intake 0.836 0.851 0.850 0.839 0.843 0.836 0.0040 NS NS NS •NS -of intake (corrected by N intake) 0.831 0.865 0.814 0.850 0.837 0.858 0.0030 ** NS * o NS N excretion in urine, g/d 31.9 32.7 37.1 33.1 36.0 31.3 1.26 * NS o * NS N retained, g/d 35.6 33.4 35.3 32.4 32.0 32.6 1.16 NS o NS NS NS -of intake 0.446 0.432 0.417 0.418 0.400 0.428 0.0142 NS NS NS NS NS -of digested 0.535 0.508 0.491 0.498 0.475 0.514 0.0174 NS NS NS o NS -g/W7 Vd 1.158 1.091 1.154 1.065 1.041 1.088 0.0377 NS NS NS NS NS Urea N, g/d 24.8 27.1 28.8 27.2 30.8 27.5 1.22 NS * NS * NS Urea N, g/W07Vd 0.769 0.862 0.905 0.857 0.970 0.868 0.0399 NS * NS * NS Biological value 0.602 0.577 0.556 0.568 0.545 0.584 0.0167 NS NS NS o NS HP = high phosphorus (P), MP = medium P, LP = low P, WB- = no wheat bran, WB+ = 100 g wheat bran/kg diet. 2 (P < 0.10) o, (P < 0.05) *, (P < 0.01) **, (P < 0.001) ***, (P > 0.10) NS Cl = WB- vs. WB + , C 2 = P lin, C 3 = P quadr, C 4 = Cl x C2, C 5 = Cl x C3 WB. No decrease in N retention due to WB was found on the LP diet. Some interactions between WB inclusion and P level were found. Adecreasing P level had a linear (p<0.05) and a curvilinear (p 0.10) NS Cl = WB- vs. WB + , C 2 = P lin, C 3 = P quadr, C 4 = Cl x C2, C 5 = Cl x C3 the earlier study, the pigs were younger and, thus, weighed less (weight 36-88 kg) than the pigs in this study (71-122 kg). Jongbloed(1987) reviewed the adaptation of young animals to widely differing amounts of P and Ca in the diet by varying their intestinal absorption, and found that a decrease in the adaptation of the intestine to dietary P and Ca restriction occurs with increasing age. This is sup- ported by the findings of NÄSI (1990): in older pigs the retention of P remained low in spite of a high P supply on a maize-soybean meal diet. Another ex- planation for the lower absorption rate of P on a LPWB- diet as compared to the earlier results may be the less favourable Ca:P ratio in this experiments (2.3 vs 1.8). A wide Ca:P ratio has an important negative influence on a low-phosphorus diet (De Wilde and Jourquin 1992). Jongbloed (1987) concludedin his trials that the higher the Ca content of the diet, the more the absorption percentage ofP and Ca decreased at increasing live weights. Phosphorus homeostasis appears to be achieved mainly by regulating excretion via urine (Linder 1991). When the P supply in the diet is low, the animal tries to retain the plasma P level constant by reabsorbing P from the kidneys. In the present study, the urinary P excretion decreased linearly (pcO.001) with a decreasing P content of the diet. The proportion of absorbed P that was retained increased linearly (p<0.001) when the P content of the diet decreased, ranging from 0.620 on a HPWB+ diet to 0.946 on a LPWB+ diet. This is in agreement with earlier observations (NÄSI 1990, NÄSI and Helander 1993). The inclusion of WB in the diet did not improve the digestibility of P. However, the amount of P excreted in urine was non-significantly lower on WB+ diets.The absorption ofP appeared to be 0.75 g/d (18.8%) higher on the LPWB+ diet compared to the LPWB- diet. The proportion of absorbed P that was retained was 7.1 percentage units, i.e. almost 1 g/d higher on the LPWB+ diet than on the LPWB- diet. The P intake was 0.5 g/d higher on a LPWB- diet, but this hardly explains the differences in ab- sorption and retention. Thus, it can be assumed that WB (phytase) had improved the utilization of phytic P on the low-P diet. The apparent P absorp- tion was found to improve by 21% in a study by Newton et al. (1983), when a corn-soybean meal diet with a normal P level was supplemented with 100 g WB. Those results are, however, not fully 33 Agricultural Science in Finland 3 (1994) Table 7. Calcium excretion, apparent digestibility and retention in pigs fed on the experimental diets. Treatment HP MP LP SEM Statistical significance WB- WB+ WB- WB+ WB- WB+ Cl C 2 C 3 C 4 C 5 Ca intake, g/d 22.11 22.41 23.08 22.08 22.85 22.44 0.118 ** NS ** *»• Ca supply in water, g/d 0.11 0.11 0.12 0.11 0.12 0.11 0.005 NS NS NS NS NS Ca excretion in faeces, g/d 14.34 15.05 15.10 14.66 15.30 14,66 0.546 NS NS NS NS NS Ca absorption, g/d 7.88 7.47 8.10 7.53 7.67 7.89 0.530 NS NS NS NS NS Ca absorption 0.355 0.332 0.349 0.339 0.335 0.352 0.0240 NS NS NS NS NS Urinary Ca excretion, g/d 0.44 0.43 0.48 0.35 0.87 1.04 0.139 NS ** * NS NS Ca retained, g/d 7.44 7.03 7.62 7.18 6.81 6.84 0.568 NS NS NS NS NS -of intake 0.335 0.312 0.328 0.324 0.296 0.304 0.0258 NS NS NS NS NS -of absorption 0.943 0.946 0.942 0.955 0.893 0.866 0.0199 NS *• NS NS NS -g/W0' 7-' 0.238 0.227 0.245 0.232 0.217 0.223 0.019 NS NS NS NS NS HP = high phosphorus (P), MP = medium P, LP = low P, WB- = no wheat bran, WB + = 100 g wheat bran/kg diet. 2 (P < 0.10) o, (P < 0.05) *, (P < 0.01) **, (P < 0.001) ***, (P > 0.10) NS Cl = WB- vs. WB + , C 2 = P lin, C 3 = P quadr, C 4 = Cl x C2, C 5 = Cl x C3 comparable with ours, because WB inclusion also enhanced the total P intake. Pointillart (1991) reported that P from a diet to which no inorganic P was added and which was supplemented by 20% of rye bran, was better absorbed (55 vs 36%) and retained (50 vs 36%) by pigs of 12-43 kg live weight than P from the control diet. The Ca intake of the pigs ranged between 22-23 g/d (Table 7). Ca digestibility was not affected by WB inclusion or by decreasing the P content of the diet, whereas urinary Ca excretion increased line- arly (p<0.01) and quadratically (p<0.05) with a decreasing dietary P content. The results of the present study show that Ca balance is mainly regu- lated through the intestine as was also concluded by Fernandez (1992). In an experiment by Den Har- tog et al. (1988) apparent faecal digestibility of Ca decreased, when the diet was supplemented with 50 gpectin, cellulose or straw meal per kg. No signifi- cant differences were found in Ca retention due to treatments. However, the retention tended to be lower on LP than on other diets. Jongbloed(1987) reported the daily Ca retention to vary from 6 to 8 g after 55 kg live weight, which is well in accordance with our results. The proportion of digested Ca that was retained decreased linearly (p<0.01) when the P content of the diet decreased. In our previous digestibility and balance study (NÄSI and Helander 1993), Ca absorption was lower in a P-supplemented diet compared to an unsupple- mented diet, but no significant differences were found in Ca retention because the urinary Ca excre- tion was also lower. POINTILLART (1991) re- ported no change in Ca absorption (53 vs. 50%) but higher Ca retention (52 vs. 45%) on a diet with 200 g inclusion of rye bran per kg feed than on a diet without any inorganic P supplement. Mg intake was higher (p<0.001) on WB+ diets and decreased when the dietary P level decreased (pcO.001) (Table 8). This indicates that both WB and dicalciumphosphate have contributed some Mg to the diet. Daily Mg absorption did not differ be- tween treatments. According to Linder (1991), dietary Ca and P do not affect the absorption ofMg 34 Agricultural Science in Finland 3 (1994) Table 8, Magnesium excretion, apparent digestibility and retention in pigs fed on the experimental diets. Treatment HP MP LP SEM Statistical significance WB- WB+ WB- WB+ WB- WB+ Cl C 2 C 3 C 4 C 5 Mg intake, g/d 5.09 5.58 5.25 5.41 4.71 5.15 0.028 *** *** **• NS *** Mg supply in water, g/d 0.50 0.50 0.56 0.50 0.55 0.52 0.022 NS NS NS NS NS Mg excretion in faeces, g/d 3.56 3.80 3.58 3.87 3.54 3.59 0.107 * NS NS NS NS Mg absorption, g/d 2.03 2.28 2.22 2.04 1.72 2.08 0.109 NS * NS NS * Mg absorption 0.361 0.374 0.382 0.344 0.327 0.367 0.0186 NS NS NS NS NS Urinary Mg excretion, g/d 0.66 0.66 0.70 0.72 0.87 0.88 0.040 NS *** NS NS NS Mg retained, g/d 1.37 1.62 1.52 1.32 0.85 1.19 0.127 NS ** NS NS * -of intake 0.243 0.246 0.261 0.223 0.163 0.212 0.0227 NS ** NS NS NS -of absorption 0.673 0.704 0.684 0.644 0.464 0.573 0.0431 NS •• NS NS NS -g/W°- 7’ 0.044 0.051 0.049 0.042 0.028 0.039 0.0038 NS •* NS NS • HP = high phosphorus (P), MP = medium P, LP = low P, WB- = no wheat bran, WB + = 100 g wheat bran/kg diet. 2 (P < 0.10) o, (P < 0.05) *, (P < 0.01) »*, (P < 0.001) ***, (P > 0.10) NS Cl = WB- vs. WB + , C 2 = P lin, C 3 = P quadr, C 4 = Cl x C2, C 5 = Cl x C3 in humans (the studies have, however, usually been done with animals). Mg homeostasis occurs simi- larly as with P, and thus, mainly via adjustments of urinary excretion in humans (Linder 1991). Ac- cording to Crenshaw (1991) the regulation of body Mg levels in pigs is not very well understood. In a study by Newton et al. (1983) WB inclusion was not found to affect the apparent digestibility of Mg in pigs in a study by Newton et al. (1983). In the present experiment, Mg excretion in urine in- creased (p<0.001) with a lower dietary P content. An interaction between WB inclusion and P level was recorded in Mg retention: on WB+ diets Mg retention decreased linearly (p<0.05) and on WB- diets both linearly (p<0.05) and curvilinearly (p 0.10) NS Cl = WB- vs. WB +, C 2 = P lin, C 3 = P quadr, C 4 = Cl x C2, C 5 = Cl x C3 WB inclusion and P level: on WB+ diets Zn reten- tion increased linearly (p<0.05) and quadratically (p<0.001) and on WB- diets it decreased quadrati- cally (p<0.001) with a decreasing dietary P level. In a study by NÄSI (1990) Zn absorption and retention were higher in diets withoutphosphate addition, but remained unaffected in a later study by NÄSI and Helander (1993). The proportion of digested Zn that was retained was higher on all WB+ diets than on WB-diets. In a trial made by Newton et al. (1983) Zn apparent absorption decreased, when the WB level of the diet increased. The indigestible, fibrous bran fraction was found to accumulate some minerals such as Zn. Unfortunately, theretention of minerals was not determined in that study. The rather low effect of WB phytase on the digestibility of P and other minerals may be due to several reasons. The optimum temperature for wheat phytase, 55°C, is higher than the animal body temperature and the optimum pH for its activity is 5.15 (Pomeranz 1978). For pigs, the stomach seems to be the principal place for the hydrolysis of phytate to utilizable P (Jongbloed 1987). The low pH of the stomach can cause the inactivation of plant phytase. The solubility of wheat phytate has been reported to be lowest within the pH range from 1.5 to 2.5 (Scheuermann et al. 1988a). According to Scheuermann et al. (1988b), pepsin also inhib- its the activity of wheat phytase. JONGBLOED (1987) found that an increase in dietary protein level improved the digestibility of P. In the present study, the pigs on WB+ diets ate less protein than the other pigs. This might also explain the low effect ofWB on P utilization. The age of the pigs may also partly explain the results. Older pigs may need less P in tissue meta- bolism and/or they are able to utilize phytate P better (Reinhart and Mahan 1986). One reason for the poor effect of WB could be that the inclusion of 100 g WB used in this experi- ment per kg diet may not have been a sufficient amount. The calculated increase in phytase activity 36 Agricultural Science in Finland 3 (1994) in the diet was only 280 U/kg. The addition level of microbiologically produced phytase for growing- finishing pigs recommended by BASF (1993) is 500 U per kg feed, having a total P content of 4.0-5.0 g/kg. The possible decreasing effect of pelleting on enzyme activity was discussed previously. Pellet- ing may, on the other hand, have a positive effect on the digestibility of P. Bayley et al. (1975) have reported improved P absorption due to steam pellet- ing. It is interesting to note that such an improve- ment was found only in diets not supplemented with inorganic P. The pelleting temperature, how- ever, was not mentioned. JONGBLOED (1987) has also reported that the absorption and retention of P improved with pelleted diets. In conclusion, the supplementation of a barley- soybean meal diet with 100 g WB per kg was not found to improve the dietary P utilization signifi- cantly. However, the digestion and retention of P appeared to be slightly improved by WB inclusion in the LP diet. This improvement may be due to WB phytase. The effects of WB on the digestibility and balance of other minerals remained relatively small. The P level had a greater effect on mineral balances. The dry matter and organic matter digest- ibilities were impaired when 100 g of WB was included in the diet. N absorption was higher on WB+ diets. The retention ofN appeared to decrease on HP and MP diets due to WB, but no decrease was found on LP diets. Ash digestibility was not affected by the treatments. The LPWB+ diet ap- peared to be the most favourable regarding the polluting P-emission„ since the faecal excretion of P on that diet was the lowest and the overall reten- tion coefficient of P was the highest. This conclu- sion can, however, be confirmed only after a growth trial. On the basis of the present results, an addition of 100 g of WB to the diet in order to improve the P utilization of finishing pigs, doesnot seem very beneficial. Acknowledgements. The authors wish to thank Ms. M. 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Vaikutus ravintoaineiden sulavuuteen ja kivennäistaseisiin Eija Helander, MattiNäsi jaKirsi Partanen Helsingin yliopisto Sulavuus- ja tasekokeessa tutkittiin, parantaako vehnäleseen fytaasi ohrasta ja soijasta peräisin olevan fosforin hyväksi- käyttöä ja voidaanko sillä näin ollen osittain tai kokonaan korvata rehuun normaalisti lisättävä epäorgaaninen fosfori. Vehnälese ei parantanut merkitsevästi fosforin hyväksi- käyttöä. Kuitenkin fosforin sulavuus japidättyminen parani- vat hieman ruokinnalla, jonka fosforitaso oli matala, kun sii- hen oli lisätty vehnälesettä. Vehnäleseen vaikutus muiden kivennäisten sulavuuteen japidättymiseen jäi vähäiseksi.Fos- foritasolla oli kivennäisten sulavuuteen ja pidättymiseen suu- rempi vaikutus. Tuhkan sulavuus pysyi muuttumattomanaeri ruokinnoilla. Kuiva-aineen ja orgaanisen aineen sulavuus heikkenivät vehnäleseen vaikutuksesta. Typen imeytymis-% oli korkeampi (pcO.Ol) vehnälesedieeteillä. Vehnälese näytti alentavan typen pidättymistä korkeimmalla ja keskinkertai- sella fosforitasolla, mutta matalalla ei. Fosforipäästöjä ajatellen matalafosforinen, vehnälesettä si- sältävä ruokinta osoittautui parhaaksi: ulosteiden fosforitaso oli alhaisin ja fosforin pidättymis-% oli korkein. Tulosten perusteella vehnäleseen käyttö sikojen rehuseoksissa fosforin hyväksikäytön parantamiseksi ei kuitenkaan näytä lupaavalta. 39 Agricultural Science in Finland 3 (1994)