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ANIMAL NUTRITION |
* University of Kentucky, Lexington 40546; and
Phibro Animal Health Co., Fairfield, NJ 07004
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Abstract |
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 Top Abstract INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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Key Words: digestibility • phosphorus • phytase • pig • virginiamycin
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INTRODUCTION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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; Dierick et al., 1986). Evaluations of the nutritional effect of subtherapeutic antibiotic supplementation have centered on effects related to the digestibility and utilization of protein and energy, because these items constitute the greatest physical and economic portion of diets. Some studies have addressed the effects of antibiotics on mineral utilization in poultry (Lindblad et al., 1954; Brown, 1957; Buresh et al., 1985), but these evaluations are limited in swine. Reports with broilers indicate that virginiamycin (VIR) has potential to improve P digestibility. Buresh et al. (1985) reported that 22 mg/kg of VIR improved P utilization in chicks fed a corn-soybean-meal (SBM) diet containing 0.47% total P. At this P level, the VIR-added diet resulted in a 4.6% increase in tibia ash compared with the same diet without VIR. Schutte et al. (1994) reported that 20 mg/kg of VIR improved ileal P digestibility by 5.5 percentage units in ileostomized roosters fed a practical diet. Because P is the most expensive mineral in swine diets, and it is associated with environmental issues, it seemed prudent to evaluate the potential effect of VIR on P digestibility in swine. The primary objective of these experiments was to evaluate VIR and phytase (PHY) effects on digestibility and on the retention and excretion of nutrients (particularly P) in growing pigs fed a P-deficient diet. This was accomplished by conducting 4 balance experiments utilizing the total collection method. An additional experiment to evaluate the long-term effects of VIR on gut microbiological profile was also conducted.
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MATERIALS AND METHODS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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All experiments were conducted under protocols approved by the University of Kentucky Institutional Animal Care and Use Committee.
A total of 70 growing-finishing barrows [Hampshire or Duroc x (Yorkshire x Landrace)] were used in 4 experiments. In each experiment, sibling pigs of similar BW within a replicate were allocated to treatments; half-siblings (i.e., a common sire) were used when enough full-siblings were not available.
In Exp. 1, sixteen barrows were fed a common grower diet for a minimum of 2 wk followed by a low-P corn-SBM-basal diet for a minimum of 10 d to standardize gastrointestinal tract conditions among the animals. Ten pigs were then selected based on overall condition, paired by genetic background, and randomly allotted within pair to 1 of 2 dietary treatments and placed in stainless steel metabolism crates. Animals had a 7-d adaptation (mean initial BW = 57.3 kg) to the crate and diet, followed by a 5-d total feces and urine collection phase. After the collection phase, the pigs were switched to the alternate dietary treatment, moved to group pens (1.22 x 2.44 m) with 2 to 3 pigs/pen for a 3-d respite from the metabolism crates. Pigs were then moved back into the crates for a repeat of the adaptation and collection procedures.
In Exp. 2, twenty-four barrows were allowed ad libitum access to the basal diet for 10 d before being allotted to 1 of 4 dietary treatments and beginning the 7-d adaptation period (mean initial BW = 63.7 kg), followed by the 5-d total collection phase.
In Exp. 3, twelve barrows were allowed ad libitum access to the basal diet for 9 d before being allotted to 1 of 4 dietary treatments and beginning the 7-d adaptation period (mean initial BW = 51.3 kg), followed by the 5-d total collection phase. As in Exp. 1, after the collection phase, the pigs were switched to the basal diet and moved to group pens (1.22 x 2.44 m) with 2 to 3 pigs/pen for a 4-d respite from the metabolism crates. Then, pigs were assigned to an alternate dietary treatment and moved back into the crates for a repeat of the adaptation and collection procedures.
In Exp. 4, twenty-four barrows were allowed ad libitum access to the basal diet for 4 d before being allotted to 1 of 4 dietary treatments and beginning the 7-d adaptation period (mean initial BW = 52.6 kg), followed by the 5-d total collection phase. For Exp. 2, 3, and 4, feeding management during the adaptation and collection phases was the same as in Exp. 1.
Dietary Treatments for Digestibility Experiments
A basal, corn-SBM diet, which was not supplemented with any inorganic source of P (Table 1), was prepared separately for each experiment. The basal diet met or exceeded all NRC (1998) nutrient requirement estimates, with the exception of P. In Exp. 1, two diets were tested: the basal diet vs. basal supplemented with VIR (Stafac 20, Phibro Animal Health Co., Fairfield, NJ). The VIR was included at 11 mg/kg, a level approved for growth promotion purposes in swine. In Exp. 2, a total of 4 diets were used with a 2 x 2 factorial arrangement of VIR and PHY (Natuphos 1200G, BASF Corp., Mount Olive, NJ). Inclusion rates of the 2 factors were 0 and 11 mg/kg of VIR and 0 and 750 PHY units (PU)/kg of diet. Exp. 3 also used a 2 x 2 factorial arrangement, with the only difference from Exp. 2 being that the intended PHY level was reduced from 750 to 300 PU/kg. The VIR and PHY premixes used in Exp. 1 to 3 came from the same bag of commercial product, with the composition label for each product used to determine the dietary inclusion rate. Experiment 4 was a repetition of Exp. 3; the PHY premix was analyzed before Exp. 4, and the result was a PHY level of 1,326 PU/g, which was the value used to calculate PHY concentration in Exp. 4 instead of the minimum value of 1,200 PU/g on the label. Actual analyzed values for the dietary treatments are provided in Table 2.
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Adaptation and Collection Procedures for Digestibility Experiments
Once the pigs were placed in the metabolism crates, the diets were weighed as individual meals into labeled plastic bags and were separated by treatment. Pigs were fed at 3% of BW during the experiments, in a gruel form, with the feed divided into 2 daily meals. The beginning and end of the collection period were marked by the addition of 0.5% indigo carmine to the morning meal. After consumption of each meal, water was added to the metabolism crate feeder to allow ad libitum access between meals. During the collection periods, the total amounts of feces were collected daily, stored in plastic bags, and frozen at –20°C until the end of the collection period. The collection of urine was initiated 14 h after the feeding of the first marked meal and was completed 14 h after the feeding of the second marked meal at the end of the collection period. A total of 150 mL of 3 N HCl was added to the collection container at the beginning of each collection to prevent volatilization of urinary N. Urine was collected every 24 h and stored at –20°C.
Sample Preparation for Digestibility Experiments
To obtain a representative sample of urine for nutrient analysis, the collected samples were thawed at room temperature and proportionally composited by weight for each pig according to the recorded daily excretion. Composited samples remained frozen at all times until analysis.
All frozen feces were dried in a forced-air oven (Tru-Temp, Hotpack Corp., Philadelphia, PA) at 55°C for 1 wk, then air-equilibrated, weighed, and ground using a Wiley laboratory mill (model 3, Arthur H. Thomas Co., Philadelphia, PA) through a 1-mm screen. All ground feces from each collection period were thoroughly mixed in a single bag for each pig. From this bag, a sample for chemical analysis was obtained and reground using a smaller high-speed grinder (type 4041, model KSM 2–4, Braun Inc., Woburn, MA). After being composited, feces were kept in a cold room at 4 to 8°C until chemical analysis.
Laboratory Analysis for Digestibility Experiments
Feces and feed were analyzed for DM content. Feces, feed, and urine were analyzed for energy, N, P, and Ca concentration; concentrations of Mg, K, Mn, Zn, Fe, Cu, and Na were assessed in all experiments, except in Exp. 3. Total contents of nutrients in feces, urine, and feed were calculated as the product of nutrient concentration and the total amount of material. Samples were analyzed at least in duplicate, and analysis was repeated when abnormal variation was observed (generally when the CV was > 5%).
Dry matter in feed and feces was assessed according to an adaptation of the AOAC (1995a) method involving overnight drying (105°C) of the samples in a convection oven (Precision Scientific Co., Chicago, IL) and then calculating moisture contents as the difference between weighings. Gross energy contents were assessed by bomb calorimetry, consisting of the ignition of samples in a pressurized-O2 environment, and measuring the heat of combustion as the amount of energy transferred to a known mass of water contained in the calorimeter (model 1261 isoperibol bomb calorimeter, Parr Instruments Co., Moline, IL). Benzoic acid pellets with known combustion heat were ignited at the beginning and end of each set of samples to verify calorimeter calibration. Feed and feces samples were assessed in duplicate by a procedure adapted from AOAC (1995a). To measure urine energy, samples were oven-dried for 2 d at 55°C into polyethylene flat bags (Jeb Plastics Inc., Wilmington, DE) before combustion. To obtain the urinary energy contents, the known heat of combustion per gram of bag material was subtracted from the total heat measured.
Nitrogen was measured using Dumas methodology in an automatic N analyzer (model FP-2000, LECO Corp., Saint Joseph, MI). Ignition of blanks and EDTA samples with known N contents was conducted daily to calibrate the equipment and to check for drift in the readings.
Phosphorus in feed and feces was assessed by a gravimetric method (modification of method 968.08; AOAC, 1990), in which samples were weighed, ashed, acid-digested, diluted to 250 mL and then reacting 50 mL of the liquid with Quimociac solution, filtered, and the precipitate obtained was weighed to calculate the P concentration. Phosphorus concentration in urine was assessed as inorganic P by a colorimetric procedure (procedure number 360-UVP, Sigma Diagnostics, St. Louis, MO) using a spectrophotometer (model Ultrospec IIE, 4057 UV/visible, LKB Biochrom Ltd., Cambridge, UK). The concentration was measured under UV light at 340 nm. A commercial reagent was used (ammonium molybdate, 0.40 mmol/L in sulfuric acid with surfactant; catalog number 360–3, Sigma Diagnostics) along with a set of 3 standards containing 1, 5, and 15 mg of P/dL (Ca/P Standard, catalog number 360–5, Sigma Diagnostics).
Except for P, all other mineral elements were assessed by flame atomic absorption spectrophotometry (Thermoelemental, SOLAAR M5, Thermo Electron Corp., Verona, WI) according to a modification of the AOAC procedure (method 927.02, 1995b).
Experimental Design and Statistical Analysis for the Digestibility Experiments
Experiment 1 challenged the null hypothesis of no effect of VIR on mineral digestibility, using 10 replications. A crossover design was used, in which a single group of 10 pigs (5 pairs by ancestry) was used in 2 collections, with each pig receiving a different treatment in each collection. The treatment structure was a 1-way treatment classification, and the experimental unit was the pig. The ANOVA was done using the GLM procedure (SAS Inst. Inc., Cary, NC). The model for analysis included the effects of collection, pair (collection), diet, and diet x collection interaction.
Experiments 2, 3, and 4 utilized a randomized complete block design. The treatment structure was a 2-way treatment classification (2 x 2 factorial) with 6 replicates per treatment, and the experimental unit was the pig. The ANOVA was also conducted using the GLM procedure of SAS. The model included the effects of collection, diet, the diet x collection interaction, and replicate (collection). Several single degree of freedom preplanned comparisons were performed. Comparisons evaluated the basal diet vs. each additive (VIR or PHY).
The error term reported is the SEM, except for Exp. 2, in which unequal numbers of observations occurred. In that case, the root mean square error is reported, which can be converted into SEM by dividing its value by the square root of the number of observations associated with each specific mean. The 
level used for determination of statistical significance was 0.05, with 
0.10 used to declare a tendency for significance.
After analysis of the individual experiments, all observations from pigs fed the basal and the basal + VIR diets were pooled for a more critical analysis. First, an ANOVA using the GLM procedure of SAS was conducted. The model included the effects of experiment, diet, the diet x experiment interaction, and replicate (experiment). The level used for determination of statistical significance was 0.05, with 0.10 used to declare a tendency for significance. Secondly, the absolute P digestibility and retention response to VIR across all experimental situations within each experiment was plotted relative to the P digestibility and retention responses of the respective control diets (either with or without PHY). The linear regression equations and associated correlation coefficients were computed for the digestibility and retention responses using the treadline formatting functions in Excel (Microsoft, Redmond, WA).
Animals, Housing Conditions, and Dietary Treatment for the Gut Microbiology Experiment
A total of 32 crossbred pigs [24 gilts and 8 barrows; Hampshire x (Yorkshire x Landrace)] with a mean BW of 29.1 x 0.50 kg were used in a 16-wk experiment to evaluate the long-term effects of VIR feeding on gut microbiological profile. Pigs of a common sire were allocated to 1 of 4 dietary treatments, and same-sex pigs were penned by pairs, resulting in 3 replications of females and 1 replication of males. The experiment was conducted in a temperature-controlled room using a total of 16 pens (1.22 x 2.44 m). Each pen was equipped with a single-hole, stainless steel self-feeder and 2 nipple waterers for ad libitum access to feed and water. The diets were fed in meal form.
Four experimental diets were based on corn and SBM, with or without VIR supplementation and with or without a partial deletion of feed-grade dicalcium phosphate (DICAL). Diet 1 was a corn-SBM diet with enough DICAL added to meet all NRC (1998) nutrient requirement estimates, including P. Diet 2 was the same as diet 1 but amended with 11 mg/kg of VIR. Diets 3 and 4 met the NRC (1998) nutrient requirement estimates, except for P. Both diets were made slightly P-deficient by deleting 0.15% DICAL. Diet 4 was amended with VIR (11 mg/kg). The treatments were thus arranged as a 2 x 2 factorial arrangement. A similar ratio of calculated dietary Ca:available P among diets was formulated for diets within each stage of growth (growing, 0.60:0.23; developing, 0.50:0.19; and finishing, 0.45:0.15).
Sampling, Laboratory Analysis, and Calculations for the Gut Microbiology Experiment
At the end of the experiment, pigs were humanely killed by exsanguination after electrical stunning. Ileal samples were taken immediately after slaughtering each pig to assess the bacterial profile and digesta pH. Samples consisted of the content from a 20-cm section of the distal ileum. Sampling involved tying both ends of the ileal section with a sterilized cotton thread, cutting the ileum portion, and transporting it on ice to the laboratory for pH determination and bacteria culturing. The quantification of phytate-utilizing bacterial populations, as colony-forming units per gram of ileal contents, was conducted according to the procedure described by Bae et al. (1999).
Experimental Design and Statistical Analysis for the Gut Microbiology Experiment
The treatment structure consisted of a 2 x 2 factorial arrangement with 4 replicate pens/treatment (pen was the experimental unit). The ANOVA was conducted using the GLM procedure of SAS. The statistical model included the effects of each factor, the interaction, and replication. The level used for determination of statistical significance was 0.05, with 0.10 used to declare a tendency for significance.
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RESULTS AND DISCUSSION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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Samples of the experimental diets were analyzed for VIR and PHY concentrations by the companies marketing the products. As expected, VIR was not detected in diets not amended with the antibiotic, whereas the other diets, with the exception of diet 4 in Exp. 3, were close to 11 mg/kg (within 25%, Table 2
). However, the assays for PHY concentration were different than expected, particularly for diets 3 and 4 in Exp. 2. It is not clear whether the differences reflect an issue with the blending of the diets or with the laboratory analysis. In Exp. 2, both were greater than their target levels and should have been at levels sufficient to maximize the PHY response; therefore, those results were retained. In Exp. 3, the assays for diets 3 and 4 were considered potentially problematic, because differences in results at these relatively low levels of PHY could cause important differences in digestibility due to the enzyme (Cromwell et al., 1995), possibly obscuring potential effects of VIR on the remaining substrate. For this reason, the results for diets 3 and 4 were disregarded for Exp. 3. In Exp. 4, the assay results were closer to those planned, and deviations across diets were deemed to be normal laboratory variation, because diet mixing practices obviated potential mixing mistakes.
Exp. 1
The addition of VIR (11 mg/kg) improved the apparent digestibility of several nutrients (Table 3). Dry matter digestibility increased by 0.94 of a percentage point (P = 0.05). A similar improvement (0.84%, P = 0.06) was observed for energy digestibility. Nitrogen digestibility was numerically but not statistically improved. In this experiment, the greatest improvement in digestibility was observed for P (8.44%, P < 0.001), followed by Ca (5.81%, P = 0.003), Zn, and Mg (3.9 and 3.1%, respectively, P = 0.02; data not shown). The observed improvement of 8.4 percentage points in P digestibility in Exp. 1 is equivalent to a release of 0.031% additional P in the diet calculated to contain 0.37% total P.
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, who used lighter pigs (35 kg of BW) in 3 balance trials to test the effects of the same level of VIR (11 mg/kg) on nutrient digestibility, mineral absorption, retention, and rate of passage in diets supplemented with P. In a 2 x 2 factorial arrangement, they supplemented VIR to a low-fiber corn-SBM meal diet (NDF: 13.5%) and to a high-fiber corn-SBM-oats diet (NDF: 20.2%) to determine if VIR would decrease the greater rate of passage expected for the high-fiber diet, thus improving nutrient utilization. In agreement with previous reports on the effects of fiber, the high-fiber diet decreased DM, energy, CP, and ash digestibility. Interestingly, it was also observed that VIR increased P digestibility in the high-fiber diet (57.7 vs. 63.0%), although it did not affect P digestibility in the low-fiber diet (55.2 vs. 55.4%). Similarly, VIR increased Ca digestibility in the high-fiber diet (56.5 vs. 66.1%) but not in the low-fiber diet (63.5 vs. 62.0%). Phosphorus and Ca retention as a percentage of absorption were also increased by VIR in the high-fiber diet (53.7 vs. 58.3% and 54.4 vs. 64.5%, respectively) but not in the low-fiber diet. Although VIR slowed the rate of passage in both diets (from 20.6 to 26.7 h), the improvement in P digestibility and retention was only observed in the high-fiber diet.
Although Ravindran et al. (1984) did not observe any effect of VIR on P digestibility in a corn-SBM diet, our study did show an improvement. The reason for the difference could be that their diets had more available P (it was supplemented with 0.90% defluorinated phosphate), whereas our diet was P-deficient, so the 2 results may not be completely comparable.
In Exp. 1, besides the improvement in P digestibility, VIR increased P retained as a percentage of absorption (P = 0.01). Among all the nutrients measured, P was the only one that showed an improvement in retention (as a percentage of absorbed) with VIR supplementation.
According to the apparent retention observed (calculated as intake minus fecal and urinary losses), VIR-treated pigs retained 0.78 more grams of P per day (3.9 g total for the 5 d) as compared with the controls. With consideration to effects of waste excretion, VIR reduced N and P excretion by 2.8% (from 28.5 to 27.7 g/d; P = 0.53) and 10.1% (from 6.11 to 5.49 g/d; P = 0.001), respectively.
Exp. 2, 3, and 4
VIR Effects.
In these experiments, a main effect of VIR on P digestibility was not observed. Nevertheless, a tendency for a VIR x PHY interaction was observed in Exp. 2 (Table 4; P = 0.06). Given that differences due to VIR were observed in Exp. 1, single degree of freedom comparisons were made between diets 1 and 2 in Exp. 2, 3, and 4. The comparisons for differences in P digestibility numerically favored VIR in all experiments, but the P-value differed: Exp. 2 (34.61 vs. 39.25%, P = 0.027), Exp. 3 (32.45 vs. 37.66%, P = 0.063), and Exp. 4 (33.40 vs. 35.18%, P = 0.44).
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Concerning P retention, expressed as a percentage of absorbed P, there was a main effect of VIR in Exp. 2 (Table 4; P = 0.03) and numerical differences in Exp. 3 and 4 (Tables 5 and 6). Virginiamycin also tended to increase P retention, expressed as a percentage of P intake (data not shown), in Exp. 3 (P = 0.08), and numerical differences were observed in Exp. 2 and 4. These differences in statistical response could suggest an equivocal response to the use of VIR. However, the digestibility and retention data can be pooled across experiments to obtain greater statistical power. When that is done (Table 7), the improvements in P and Ca responses are unequivocal. Across experiments, the average improvement in P digestibility by amending the basal diet with VIR was 5.0% (range: 1.78 to 8.44%; P < 0.001), whereas the average improvement in P retention (as a percentage of absorption) was 1.0% (range: 0.07 to 2.36%; P = 0.004). Averaging values from the 4 experiments, the decrease in total P excreted due to VIR amendment was 4.9% (data not shown; P = 0.006).
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). Results from Exp. 2 indicate that this level of PHY inclusion increased P digestibility 78.9% (from 34.6 to 61.9%) for the basal diet and 55.4% (from 39.3 to 61.0%) for the VIR-added diet (P < 0.001). As expected, a smaller effect on P digestibility was observed when PHY level was reduced to 300 PU in Exp. 4, which agrees with earlier reports of linear responses to different levels of PHY (Lei et al., 1993; Veum et al., 1994; Cromwell et al., 1995).
In Exp. 2, no effect of PHY on DM, energy, or N digestibility was observed. But, PHY did improve Ca digestibility in both Exp. 2 and 4 (Tables 4 and 6, respectively; P < 0.001), which is in agreement with other reports (Lei et al., 1993; Pallauf et al., 1994; Jongbloed et al., 1999b).
In Exp. 2 (Table 4), the tendency for an interaction between PHY and VIR for P and Ca digestibility (P < 0.10), along with the lack of significant difference between diets 3 and 4, indicated that the level of inclusion of PHY was probably high enough to release a large proportion of the phytate P present in the diet, not leaving any room for further VIR effect. This observation motivated reduction of the PHY level in Exp. 3 and 4 to facilitate detection of any possible additive effects of VIR.
As expected, a smaller response in digestibility was observed when the level of PHY was lowered in Exp. 4 (Table 6). It is known that there is a dose-response relationship between the level of PHY and the apparent total tract P digestibility in pigs fed corn-SBM diets (Cromwell et al., 1995; Harper et al., 1997; Jongbloed et al., 1999a). In Exp. 2, comparisons between diets 1 and 3 showed that PHY increased P digestibility 79% (from 34.6 to 61.9%, P < 0.01; Table 4), but it was only 41% (from 33.4 to 47.2%, P < 0.01) in Exp. 4 (Table 6). Phosphorus retention (g/d) was also increased by PHY additions (P < 0.001); the percentage increases resemble the changes observed in P digestibility.
Reflecting the increase in digestibility and retention observed with the PHY amendments, total P excretion was notably reduced by PHY. In Exp. 2 (Table 4), PHY decreased (P < 0.001) total P excretion of the basal diet by 36.6% (from 4.8 to 3.1 g/d) and by 34.9% (from 4.7 to 3.1 g/d) in the VIR-added diet. Smaller decreases in P excretion were observed when the PHY level was reduced to 300 PU in Exp. 4. In Exp. 4 (Table 6), P excretion decreased (P = 0.001) 20.1% for the basal diet (from 4.3 to 3.4 g/d) and 21.2% for the VIR-added diet (from 4.2 to 3.3 g/d).
From the results of the 4 experiments (Table 7), it was evident that VIR amendment improved apparent P digestibility by approximately 5%. In addition, the PHY amendment results confirmed the positive effects of this enzyme on digestibility, retention, and excretion. But, there were differences in the VIR response across experiment and level of PHY supplementation. The relative P response across all situations is best assessed in the manner presented in Figure 1, in which the P responses for VIR are plotted against the P digestibility of their respective controls (either with or without PHY). It is evident that the magnitude of improvement is dependent on the digestibility of the control; specifically, the magnitude of increase in P digestibility due to VIR tended to be inversely related to the P digestibility of the control diet. It should be noted that there is a VIR digestibility response in diets containing PHY if PHY used is not the level that can maximize P digestibility. That is, there is potential for an additivity of response to the 2 factors evaluated in these experiments
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arrived at a similar conclusion for chicks and poults fed Ca- and P-deficient diets supplemented with aureomycin. They showed that in the absence of the antibiotic, maximum BW gain was obtained with a diet containing 1.0% Ca and 0.6% inorganic P. However, in the presence of aureomycin, maximum gain and efficiency of feed utilization resulted when P was decreased to 0.4%. Increasing P above 0.4% in the diet containing antibiotic did not increase the gain. The researchers concluded that the more inadequate the Ca and P in the diet, the greater the percentage increase in BW gain was achieved from the antibiotic.
The inverse relationship observed between the level of improvement in P digestibility and the digestibility level of the basal diet is in agreement with the conclusions of Braude and Johnson (1953) relative to effects of antibiotic on growth. Those researchers summarized many experiments with different antibiotics to conclude that the relative improvement in growth resulting from antibiotic amendments was inversely related to the growth rate of the control pigs.
Gut Microbiology Experiment
The long-term feeding of VIR in both the control diet and the diet with a marginally reduced P level resulted in a change in ileal microbial profile (Table 8). Phytate-utilizing bacteria were the intestinal organisms of greatest interest. A positive increment in the number of these bacteria was observed in both the normal and P-deleted diets when VIR was added, although the differences were not statistically significant (P = 0.13). This numerical difference represents logarithm increments of 12.4 and 17.2% over the respective controls. No literature reports were found on the effects of antibiotics on phytate-utilizing bacteria. The addition of VIR also tended to affect lactobacilli populations (main effect, P = 0.11; interaction, P = 0.02). Virginiamycin strongly decreased lactobacilli in the normal-P diet but did not affect this bacterial population in the P-deleted diet. The observed results on changes in lactobacilli numbers in the normal-P diet amended with VIR agree with the results of Collier et al. (2003), who reported a decrease in lactobacilli counts in pigs fed a rotating sequence of antibiotics, including VIR. Other researchers have shown decreasing numbers of lactobacilli in the feces and incubated ileal contents of pigs fed different antibiotics (Andersen, 1954; Vervaeke et al., 1979). Because lactobacilli are abundant populations of acid-producing bacteria, an increase in ileal pH would also be expected to coincide with a lactobacilli population decrease. Nevertheless, no difference in pH was observed in this experiment. Collier et al. (2003) did not provide data on pH changes, whereas Vervaeke et al. (1979) reported a decrease in lactobacilli numbers that was associated with a corresponding increase in pH for ileal contents of pigs fed VIR. Due to known differences in populations of dominant bacterial species in the different segments of the small intestine (Fewins et al., 1957), and taking into account that the major site of Ca and P absorption is the jejunum (Crenshaw, 2001), it might be important for future research to also assess microbial populations and pH differences at the jejunum.
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Footnotes |
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2 Appreciation is expressed to A. de Souza, E. Xavier, T. Meyer, A. Pettey, C. Elmore, B. Kim, and N. Inocencio for assistance in the care of pigs and in laboratory analysis; to D. Higginbotham for help in diet preparation; and to Akey Inc., Lewisburg, Ohio, for ingredients used in the experiments at the University of Kentucky.
3 Current address: Universidad de Antioquia, Medellin, Colombia.
4 Corresponding author: mdlind1{at}uky.edu
Received for publication November 6, 2006. Accepted for publication April 20, 2007.
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LITERATURE CITED |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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