| Livestock Research for Rural Development 27 (7) 2015 | Guide for preparation of papers | LRRD Newsletter | Citation of this paper |
The effects of xylanase and phytase supplementation on energy digestibility, site of nutrient digestion, and pH content in the gastrointestinal tract (GIT) and on growth performance were studied in diets with reduced nutrient specifications fed to weaned pigs. The experiment was designed as a 2 x 2 factorial plus a positive control diet containing14.65 MJ digestible energy (DE)/kg, 0.65% total phosphorous (P), and 0.80% calcium (Ca).
Phosphorous and Ca contents were reduced by 10% and the DE content by 0.62 MJ/kg in the other 4 diets. Weaned pigs (8.6 ± 0.5 kg initial body weight)were fed 1 of 5 diets for 21 d. Feeding a nutrient reduced diet lowered total tract energy digestibility. Xylanase and phytase improved the total tract DE content of the negative control diet (NC). Xylanase improved energy digestibility of NC in the mid jejunum and over the total tract by 63.0 and 4.6% respectively. Phytase improved the DE content of NC by 0.64 MJ/kg. Feeding a nutrient reduced diet tended to reduce the pH content of the upper small intestine (SI), and phytase raised the pH content of the upper mid SI. Overall phytase improved body weight (BW) and the average daily gain (ADG) of NC. Xylanase and phytase improved total tract DE content and growth performance of weaned pigs fed nutrient reduced diets. Phytase inclusion led to a faster return to alkaline conditions in the upper SI. Exogenous enzymes can be used to improve digestibility of nutrient-reduced diets based on wheat and millrun for weaned pigs.
Keywords: digesta, enzymes, millrun, pH content
Plant carbohydrates such as starch and fibre are the most common energy source for monogastrics (Bach Knudsen and Canibe 2000). In developing countries like Ghana, high-fibre Agro Industrial By-products (AIBP) and waste grains not intended or suitable for human consumption make up the bulk of monogastric feed ingredients (Nortey et al 2013; Manu-Barfo et al 2013). Their use may increase hindgut fermentation resulting in inefficient energy utilization (Suarez-Belloch et al 2013). An example of such an AIBP is wheat millrun. Although the cultivation of wheat in West Africa is not widely practised, most countries within the sub-region import large quantities of wheat. Nigeria has one of the largest flour milling complexes in the world with a total installed capacity of 8000 metric tonnes of raw wheat per day. Large multinational companies also own and operate may flour mills in Liberia, Gambia, Ghana and Sierra Leone (Seaboard Overseas and Trading Group 2015). In Ghana some flour/feed mills also import low-grade wheat purposely for use in animal feed manufacturing. With a total installed flour milling capacity of approximately 3,000 tonnes of wheat per day, operating at around 75% efficiency, and a flour extraction rate of approximately 75%, flour mills in Ghana alone can potentially produce 562 tonnes of milling by-products per day. One of such by-products is wheat millrun. It is a by-product of flour milling and consists of fine and coarse particles of wheat bran, wheat shorts, wheat middling and “offals” from the “tail of the mill”, (AAFCO 1998). During the milling process, individual by-products tend to lose their identity and therefore most flour mills simply bulk them together and label it as wheat bran or wheat millrun. Pigs do not digest high fibre diets like wheat bran well, because the necessary endogenous enzymes for non-starch polysaccharide hydrolysis are lacking (Barrera et al 2004). Ingredients of plant origin also present phosphorous to pigs in the form of phytate phosphorous that is not easily available, because pigs do not have endogenous phytase required to hydrolyse phytate P (Humer et al 2014). Exogenous xylanase and phytase may improve digestibility of high fibre and phytate-based diets for swine by increasing the availability of energy, phosphorous, amino acids, and calcium (Nortey et al 2007). Effects of xylanase and phytase on growth performance have been inconsistent (Bedford et al 1992; Van Lunen and Schulze 1996; Bedford and Schulze 1998; Nortey et al 2007). The kinetics of nutrient digestion within the gastrointestinal tract may be studied using the slaughter technique and this can provide evidence for the changes in site of nutrient digestion and physiological characteristics of digesta following enzyme supplementation. The pH content of the gastro intestinal tract (GIT) may be partly related to the volatile fatty acid content that may be a result of the type and quantity of fibre in the diet, the buffering capacity of dietary nutrients and on the acid dissociation constant (pKa) of the gastrointestinal tract (Pluske et al 2003).
The hypothesis of the present study is that adding xylanase and phytase to a diet for weaned pigs based partly on wheat millrun and reduced in nutrient specification will improve energy digestibility and change digesta pH profile throughout the GIT. The objectives were: 1) to study the effect of xylanase and phytase and their interaction on the site of energy digestion in weaned pigs fed diets based on millrun, and 2) to study the effect of xylanase and phytase on the pH of the GIT.
Effects of xylanase (0 or 4,375 units/kg feed) and (or) phytase supplementation (0 or 500 phytase units/kg feed) were studied in a 2 x 2 factorial arrangement in a diet with reduced nutrient specifications (negative control), together with a positive control diet, for a total of 5 diets in a fractional factorial arrangement. The positive control diet was formulated to be at requirement for all nutrients. The negative control diet was formulated to be low in energy by 0.62 MJ/kg, and in dietary Lys, Met, Thr, P and Ca by 10% (Table 1). The xylanase was endo-1, 4-β-xylanase (EC 3.2.1.8; Porzyme 9300; Danisco Animal Nutrition, Marlborough, UK), and the phytase was 6-phytase (EC 3.3.26; Phyzyme XP; Danisco Animal Nutrition). All diets contained 7.5% wheat millrun. The millrun contained the screenings, bran, and short fractions but not the middlings fraction after flour milling of hard red spring wheat. The wheat control diet was formulated to contain 14.65 MJ/kg DE and 0.78 g true ileal digestible lysine/MJ DE. To the diets, 1% acid-insoluble ash was added to serve as a marker for digestibility calculations.The animal protocol for the study was approved by the University of Alberta Faculty Animal Policy and Welfare Committee, and followed established principles (CCAC, 1993). The experiment was conducted at the Swine Research and Technology Centre of the University of Alberta (Edmonton, Alberta, Canada).
Twenty five weaned pigs (Large White x Duroc; Genex Hybrid; Hypor, Regina, Saskatchewan, Canada; initial BW, 8.6 ± 0.5 kg) were housed in individual pens (1 x 0.5 x 0.8 m; length x width x height) that allowed freedom of movement. The floor of the pens was plastic coated expanded metal and each pen had an individual feeder and nipple drinker. Each pig was randomly fed 1 of 5 diets in one period of 21 d resulting in 5 observations per diet. Pigs were weighed at the beginning of the experimental period (d 0), and weekly thereafter (d 7, 14, and 21). On each weigh day, feed disappearance was determined, and the combined data were used to calculate ADG, average daily feed intake (ADFI), and feed efficiency (Gain:Feed).
Faeces were collected for 8 h on d 18 and 19, pooled by pig and frozen at –20șC. On d 21, pigs were euthanized and the GIT removed. The GIT was laid on a table and the small intestine divided into 4 segments of equal length. The contents of the stomach, upper small intestine (segment 1), mid jejunum (segment 2), lower-mid small intestine (segment 3), lower small intestine (segment 4), cecum, mid-colon, and rectum were carefully emptied into plastic containers. The pH content of the segments was measured (Accumet Basic AB 15 pH meter, Fisher Scientific) and samples were immediately frozen at –20șC for later analyses. Prior to analyses, faeces and digesta were thawed, homogenized, and freeze-dried. Feed and freeze-dried faeces were ground finely over a 1-mm screen. Digesta was ground over a 0.5-mm screen and together with feed were analysed for non-starch polysaccharides. Feed and faeces were analysed for DM by drying at 135șC in an airflow-type oven for 2 h (Method 930.15; AOAC, 1990). Acid-insoluble ash content was analysed by the method of Van Keulen and Young (1977). The GE of feed, faeces, and digesta was determined adiabatically using an automatic bomb calorimeter (model AC-300, Leco Corporation, St. Joseph, MI). Diet and lower small intestinal samples were analysed for soluble and insoluble non starch polysaccharides and constituent sugars by gas liquid chromatography (Englyst and Hudson, 1987).
Based on the results of chemical analysis, ileal and total-tract digestibility of gross energy (GE) and dry matter (DM), and digestible energy (DE) content were calculated using the acid-insoluble ash concentration of feed, digesta and faeces (Adeola 2001). The energy and acid insoluble ash contents of 3 additional segments of the small intestine (upper, upper-mid, and lower-mid small intestine) were analysed to determine energy digestibility, and together with results from the terminal ileum, energy disappearance along the GIT was determined.
To compare the differences in total tract digestibility of DM and energy between the diets, data was analysed by ANOVA using the GLM procedure within SAS (SAS Inst. Inc., Cary, NC, 1999). Pig was considered the experimental unit. Ileal digestibility data along the different segments of the gastrointestinal tract and also the performance data were analysed by the PROC MIXED procedure within SAS as a Completely Randomized Design. Main effects of xylanase, phytase, and their interaction term were determined in the diets with reduced nutrient specifications. The negative control diet was compared to the positive control diets using a contrast statement.
Total tract energy digestibility was depressed by 3.6 %-units when the nutrient profile was reduced (Table 2). When used together, there was a positive interaction between xylanase and phytase on energy digestibility in the mid colon and for the total tract. Xylanase improved energy digestibility of the negative control diet by 23 %-and 3.8% units in the mid jejunum and over the total tract respectively.
| Table 1. Ingredient and calculated nutrient composition (as-fed basis) of the negative and positive control diets¹ | ||
| Ingredients, g/kg diet | Positive control | Negative control |
| Wheat | 555 | 649 |
| Soybean meal | 260 | 210 |
| Wheat millrun | 75.0 | 75.0 |
| Canola oil | 34.0 | 04.0 |
| Spray dried whey | 15.0 | 10.0 |
| Herring meal | 15.0 | 10.0 |
| Limestone | 12.2 | 12.3 |
| Celite | 10.0 | 10.0 |
| Dicalcium phosphate | 7.3 | 3.6 |
| Vitamin premix2 | 5.0 | 5.0 |
| Mineral premix3 | 5.0 | 5.0 |
| Salt | 2.0 | 2.0 |
| Choline chloride | 1.2 | – |
| L-Lys HCl | 3.0 | 3.5 |
| L-Thr | 0.6 | 0.3 |
| DL-Met | 0.1 | – |
| Calculated nutrient content | ||
| DE, MJ/kg | 14.65 | 14.03 |
| ME, MJ/kg | 13.69 | 13.06 |
| CP, g/kg | 224.0 | 209.6 |
| CF,g/kg | 26.9 | 27.6 |
| True digestible Lys, g/MJ DE | 0.78 | 0.57 |
| Total Lys, g/kg | 13.5 | 12.5 |
| True ileal digestible Lys, g/kg | 11.4 | 8.1 |
| Total P, g/kg | 6.5 | 5.5 |
| Available P, g/kg | 3.6 | 2.7 |
| Ca, g/kg | 8.0 | 7.0 |
|
¹Xylanase was included at 167 g/1,000 kg of
finished feed, and phytase was included at 100 g/1,000 kg of finished
feed to create the enzyme-supplemented diets. ²Supplied per kilogram of diet: 8,250 IU of vitamin A, 825 IU of vitamin D3, 40 IU of vitamin E, 35 mg of niacin, 15 mg of D-pantothenic acid, 5 mg of riboflavin, 4 mg of menadione, 2 mg of folic acid, 1 mg of thiamine, 0.2 mg of D-biotin and 0.025 mg of vitamin B12. ³Supplied per kilogram of diet: 100 mg of Zn, 80 mg of Fe, 50 mg of Cu, 25 mg of Mn, 0.5 mg of I, and 0.1 mg of Se. |
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Xylanase and phytase independently improved the total tract DE content of the negative control diet by 0.96 and 0.64 MJ/kg, respectively, but the effect of the combined supplementation did not equal their cumulative effects. The DE content of the negative control diet with xylanase was equal to the DE content of the positive control diet. Xylanase and phytase interacted to increase the pH of the mid jejunum. Phytase alone increased the pH in the upper mid jejunum by 0.53. In the lower-mid small intestine, the two enzymes together tended to interact to affect digesta pH of the GIT. Xylanase improved BW of pigs fed the negative control diet on d 21 by 1.7 kg. On d 14, phytase improved BW on d 21 by 2.1 kg. Overall from d 0 to 21, enzymes did not affect ADFI. Reducing the energy content of the diet reduced ADG between d 8 to 14 and d 15 to 21 by 0.18 and 0.20 kg/d respectively. Xylanase improved overall G:F for d 0 to 21 by 0.06. Phytase did not affect G:F, and an interaction between xylanase and phytase was not observed.
For weaned pigs, selection of feedstuffs for feed is based among others on formulating initial diets with highly digestible ingredients that will complement the pattern of digestive enzymes, and digestive enzyme development in the GIT (Tokach et al 2003). In the current study, ingredient selection was not necessarily based on the above criteria. Wheat millrun contains more of the less-digestible ingredients such as fibre compared to wheat (Souffrant, 2001; Svihus and Gullord 2002; Slominski et al 2004). For this trial, the energy level was brought down by reducing the content of highly digestible feedstuffs such as soybean meal, herring meal, spray dried whey, and canola oil, while keeping the level of millrun constant. This could explain the reduction in digestibility and growth performance. The pH of the GIT contents was influenced by dietary nutrient level. The dietary fibre content for the present study was relatively constant; hence the changes in digesta pH may likely be due to the buffering capacity of dietary nutrients rather than the quantity of fibre or VFA (Dersjant-Li et al 2001; Pluske et al 2003).
Within individual segments, the greatest impact of enzymes was observed with xylanase in the mid jejunum, as was reflected in an improved total tract energy digestibility and DE content. This suggests that xylanase supplementation caused hydrolysis of NSP to occur in the upper parts of the GIT, specifically the small intestine. The pig benefits energetically following such a shift, because enzymatic hydrolysis in the small intestine is a more efficient process of energy transformation than hindgut fermentation (Anguita et al 2006). In the present study, xylanase supplementation improved energy digestibility and DE contents so that the improved coefficients were similar to the positive control diet, similar to previous studies (Nortey et al 2007; Hanczakowskat et al 2012) indicating that adding fibre-degrading enzymes to diets high in NSP can improve energy digestibility and utilization.
For the type of diet used in the present study containing millrun, the content of phytic acid will be high compared to a diet without this by-product. Adding phytase to the negative control diets in the present study improved total tract DE content. Phytase increased the pH content of the mid jejunum indicating a more rapid shift of the GIT contents from a state of acidity to one of neutrality. In addition to producing enzymes for carbohydrate digestion, the small intestine also secretes alkaline pancreatic juice and bile fluids that convert the acid chyme entering from the stomach to a more alkaline material (Yen 2001). The conversion to more alkaline conditions provides an optimum pH environment for intestinal enzyme activity. Providing an optimum environment for enzymatic action in the proximal small intestine may reduce the amount of nutrients escaping enzymatic hydrolyses and which will eventually end up as substrates for microbial fermention in the large intestine.
| Table 2. Effect of xylanase and phytase supplementation on apparent ileal and total tract energy and DM digestibility and DE content in different segments of the GIT of a diet with reduced nutrient specifications and a positive control diet fed to weaned pigs¹ | ||||||||||
| Item | Reduced nutrient specifications |
Pooled SEM |
P-value² | |||||||
| PCON | NCON | XYL | PHY |
XYL + PHY |
PCON vs. NCON |
XYL | PHY | XYL x PHY | ||
| Energy digestibility | ||||||||||
| Mid jejunum | 49.6 | 36.5 | 59.5 | 43.6 | 51.2 | 4.87 | 0.072 | 0.005 | 0.901 | 0.132 |
| Terminal ileum | 60.2 | 50.6 | 62.6 | 59.6 | 59.2 | 8.35 | 0.687 | 0.687 | 0.953 | 0.656 |
| Mid colon | 84.3 | 81.2 | 84.3 | 83.7 | 82.4 | 1.09 | 0.066 | 0.422 | 0.855 | 0.059 |
| Total tract | 85.5a | 81.9b | 85.7a | 84.0ab | 84.9a | 0.76 | 0.003 | 0.005 | 0.433 | 0.070 |
| DE, MJ/kg | ||||||||||
| Mid jejunum, as-is | 1.99 | 1.41 | 2.34 | 1.71 | 2.04 | 0.19 | 0.045 | 0.004 | 0.988 | 0.136 |
| Terminal ileum, as-is | 2.40 | 2.09 | 2.46 | 2.30 | 2.37 | 0.32 | 0.624 | 0.591 | 0.935 | 0.652 |
| Mid colon, as-is | 3.38 | 3.18 | 3.32 | 3.30 | 3.29 | 0.05 | 0.001 | 0.580 | 0.195 | 0.131 |
| Total tract, DM | 16.1a | 15.0b | 15.9a | 15.7a | 16.0a | 0.14 | <0.001 | <0.001 | 0.021 | 0.045 |
|
a,bMeans within a row without a common superscript
differ (P< 0.05). ¹Treatment means represent least squares means. Twenty five weaned pigs (8.6 ± 0.5 kg) each fed one of five diets in one period of 21 d for 5 observations per diet. PCON = positive control; NCON = negative control; XYL = xylanase; PHY = phytase. ²The P-values of orthogonal contrasts for XYL, PHY, and XYL x PHY are among the 4 diets with reduced nutrient specifications. For orthogonal contrasts, XYL= compares diets with xylanase to those without; PHY= compares diets with phytase to those without; XYLxPHY= compares (NCON and XYL+PHY) to (XYL and PHY) |
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| Table 3. Effect of xylanase and phytase supplementation on pH of contents of different portions of the small intestine (SI) in weaned pigs¹ | ||||||||||
| Reduced nutrient specifications |
Pooled SEM |
P-value² | ||||||||
| pH | PCON | NCON | XYL | PHY | XYL + PHY |
PCON vs. NCON |
XYL | PHY | XYL x PHY | |
| Upper SI | 5.84 | 5.82 | 5.94 | 5.90 | 5.90 | 0.074 | 0.420 | 0.779 | 0.436 | 0.836 |
| Upper mid SI | 6.34ab | 5.98c | 6.14bc | 6.51a | 6.22abc | 0.104 | 0.024 | 0.532 | 0.008 | 0.037 |
| Lower mid SI | 6.57ab | 5.97b | 6.33ab | 6.71a | 6.22ab | 0.230 | 0.081 | 0.781 | 0.187 | 0.084 |
| Lower SI | 6.26 | 5.99 | 6.11 | 6.31 | 6.22 | 0.221 | 0.398 | 0.947 | 0.640 | 0.398 |
|
a,b,cMeans within a row without a common
superscript differ (P< 0.05). ¹Treatment means represent least squares means. Twenty five weaned pigs (8.6 ± 0.5 kg) each fed one of five diets in one period of 21 d for 5 observations per diet. PCON = positive control; NCON = negative control; XYL = xylanase; PHY = phytase. ²The P-values of orthogonal contrasts for XYL, PHY, and XYL x PHY are among the 4 diets with reduced nutrient specifications. For orthogonal contrasts, XYL= compares diets with xylanase to those without; PHY= compares diets with phytase to those without; XYLxPHY= compares (NCON and XYL+PHY) to (XYL and PHY) |
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| Table 4. Effect of wheat millrun inclusion level, and xylanase and phytase supplementation, either individually or in combination to wheat-based diets on performance of weaned pigs over time¹ | ||||||||||
| Reduced nutrient specifications |
Pooled SEM |
P-value³ | ||||||||
| Item | PCON | NCON | XYL | PHY | XYL + PHY |
PCON vs. NCON |
XYL | PHY | XYL x PHY | |
| BW, kg | ||||||||||
| D 7 | 11.4 | 11.2 | 11.3 | 11.2 | 11.8 | 0.58 | 0.675 | 0.263 | 0.420 | 0.295 |
| D 14 | 16.8 | 15.4 | 16.0 | 16.4 | 16.8 | 0.90 | 0.034 | 0.231 | 0.068 | 0.771 |
| d 21 | 21.8 | 19.1 | 20.8 | 21.2 | 22.1 | 0.99 | <0.001 | 0.019 | <0.01 | 0.393 |
| ADFI, kg/d | ||||||||||
| D 0 to 7 | 0.45 | 0.57 | 0.50 | 0.55 | 0.52 | 0.06 | 0.161 | 0.364 | 0.952 | 0.684 |
| D 8 to 14 | 1.05 | 0.97 | 1.00 | 1.11 | 1.05 | 0.06 | 0.304 | 0.813 | 0.099 | 0.450 |
| D 15 to 21 | 1.09ab | 1.00b | 1.18ab | 1.23a | 1.19ab | 0.06 | 0.299 | 0.260 | 0.066 | 0.083 |
| D 0 to 21 | 0.86 | 0.84 | 0.89 | 0.96 | 0.92 | 0.08 | 0.847 | 0.993 | 0.344 | 0.569 |
| ADG, kg/d | ||||||||||
| D 0 to 7 | 0.39 | 0.37 | 0.37 | 0.36 | 0.45 | 0.05 | 0.680 | 0.324 | 0.453 | 0.352 |
| D 8 to 14 | 0.77 | 0.59 | 0.68 | 0.74 | 0.71 | 0.04 | <0.001 | 0.468 | 0.048 | 0.162 |
| D 15 to 21 | 0.78 | 0.58 | 0.74 | 0.76 | 0.83 | 0.05 | <0.001 | 0.026 | 0.014 | 0.353 |
| D 0 to 21 | 0.65 | 0.51 | 0.59 | 0.62 | 0.66 | 0.05 | 0.049 | 0.191 | 0.082 | 0.651 |
| G:F | ||||||||||
| D 0 to 7 | 0.89 | 0.68 | 0.74 | 0.69 | 0.88 | 0.08 | 0.103 | 0.195 | 0.408 | 0.474 |
| D8 to 14 | 0.73a | 0.62b | 0.69ab | 0.67ab | 0.68ab | 0.03 | 0.025 | 0.247 | 0.553 | 0.347 |
| D 15 to 21 | 0.73 | 0.60 | 0.63 | 0.62 | 0.70 | 0.05 | 0.073 | 0.226 | 0.388 | 0.565 |
| D 0 to 21 | 0.78 | 0.63 | 0.69 | 0.66 | 0.75 | 0.04 | <0.01 | 0.047 | 0.210 | 0.579 |
|
a,bMeans within a row without a common superscript
differ (P< 0.05). ¹Treatment means represent least squares means. PCON = positive control; NCON = negative control; XYL = xylanase; PHY = phytase. ²The P-values of orthogonal contrasts for XYL, PHY, and XYL x PHY are among the 4 diets with reduced nutrient specifications. For orthogonal contrasts, XYL= compares diets with xylanase to those without; PHY= compares diets with phytase to those without; XYLxPHY= compares (NCON and XYL+PHY) to (XYL and PHY) |
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Results of the present study indicate that phytase may help prevent that shift from enzymatic hydrolysis to microbial fermentation by providing an optimum pH in the upper GIT. Phytase inclusion also improved BW at d 21, which could be partly due to improved energy utilization. The effects of xylanase and phytase on nutrient digestibility were not synergistic. For synergy to occur, the combined supplementation of xylanase and phytase must provide an effect that is at least equal to the sum of effects of the individual enzymes. The lack of synergy may suggest that the effects of the individual enzymes may overlap in the responses observed in the pigs. Thus a combined supplementation of xylanase and phytase in a diet may not produce a synergistic effect due to an overlapping effect of the individual enzymes on common response variables (Woyengo et al 2010).
Phytase inclusion led to an increase in the pH content of the proximal small intestine which may reduce the amount of nutrients that may be fermented in the large intestine. This shift may ultimately result in improvement in energy utilization and therefore improved performance. Xylanase and phytase have the potential to improve nutrient digestibility of a diet with reduced nutrient specifications to coefficients similar to a positive control. The uplift in digestibility can improve growth performance, which in the present study was a result of improved G:F.
Since large quantities of wheat by-products like millrun ultimately end up as ingredients for monogastric feed manufacture, knowing how to obtain the maximum benefit from this ingredient will be of great value to farmers in Ghana, and indeed the whole West African sub-region. From the West African perspective, this study is novel and provides some justification for farmers to consider the use of appropriate enzymes in order to take advantage of the vast ingredient resources available in West Africa. A greater dependence and efficient use of unconventional feed ingredients including by products like millrun, will ultimately reduce the competition between man and livestock for traditional energy sources like corn, reduce the cost of feed and ultimately the cost of meat.
Supported by funding from Danisco Animal Nutrition, Saskatchewan Agriculture Development Fund, Sask Pork, Alberta Pork, and Manitoba Pork Council. The authors acknowledge Dawn Foods for the wheat millrun.
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Received 22 January 2015; Accepted 7 May 2015; Published 2 July 2015