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J. Anim Sci. 2007. 85:459-467. doi:10.2527/jas.2005-630
© 2007 American Society of Animal Science
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ANIMAL PRODUCTION

Effects of Acid LAC and Kem-Gest acid blends on growth performance and microbial shedding in weanling pigs1,2

M. C. Walsh*, D. M. Sholly*, R. B. Hinson*, S. A. Trapp*, A. L. Sutton*, J. S. Radcliffe*, J. W. Smith, II{dagger},3 and B. T. Richert*,4

* Department of Animal Science, Purdue University, West Lafayette, IN 47907; and and {dagger} Kemin Americas Inc., Des Moines, IA


   Abstract
Top
 Abstract
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 LITERATURE CITED
 
Weanling pigs with mean initial BW of 6.04 kg (Exp.1) and 5.65 kg (Exp. 2) and mean age at weaning of 18.2 d (Exp. 1) and 17.7 d (Exp. 2) were used in two 5-wk experiments (Exp. 1, n = 180; Exp. 2, n = 300) to evaluate the effects of an organic acid blend (Acid LAC, Kemin Americas Inc., Des Moines, IA) and an inorganic/organic acid blend (Kem-Gest, Kemin Americas Inc.) on weanling pig growth performance and microbial shedding. In Exp. 1, the 5 dietary treatments were 1) negative control, 2) diet 1 + 55 ppm carbadox, 3) diet 1 + 0.4% Acid LAC, 4) diet 1 + 0.2% Kem-Gest, 5) diet 1 + 0.4% Acid LAC and 0.2% Kem-Gest. In Exp. 2, the 6 dietary treatments were diets 1 through 4 corresponding to Exp. 1, plus 5) sequence 1: 0.4% Acid LAC for 7 d followed by 0.2% Kem-Gest for 28 d, and 6) sequence 2: 0.2% Kem-Gest for 7 d followed by 0.4% Acid LAC for 28 d. Pigs were housed at 6 (Exp. 1) or 10 (Exp. 2) pigs/pen. Treatments were fed throughout the experiment in 3 phases: d 0 to 7, d 7 to 21, and d 21 to 35. In Exp. 1, there were no differences (P > 0.05) in ADG, ADFI, or G:F among the dietary treatments at any time during the study. In Exp. 2, throughout the study, pigs fed carbadox (diet 2) and sequence 1 (diet 5) diets had the greatest ADG (d 0 to 35; 262, 294, 257, 257, 292, and 261 g/d, diets 1 through 6, respectively; P < 0.05), greater ADFI than all other acid treatments (P < 0.05), and tended to have greater ADFI than diet 1 (P < 0.10). Fecal pH, Escherichia coli concentrations, and Salmonella presence were determined at d 6, 20, and 34 for Exp. 1, and on d 32 for Exp. 2. For both experiments, there was no effect of treatment on the presence of fecal Salmonella (P > 0.10) at any sampling time. In Exp. 1, fecal E. coli concentrations for pigs fed the carbadox (P < 0.05) diet were greater than for pigs fed the combination diet with 0.4% Acid LAC and 0.2% Kem-Gest on d 34, and the pigs fed the negative control diet tended (P < 0.10) to have greater fecal E. coli concentrations than those fed the combination diet on d 34. In Exp. 2, fecal pH of pigs fed sequence 1 tended to be greater than fecal pH of pigs fed diet 1, diet 4, or sequence 2 (P < 0.10), but there was no dietary effect on fecal E. coli. In Exp. 1, growth performance of pigs fed the Acid LAC and Kem-Gest diets was similar to each other and to that of the carbadox-fed pigs. Adding the combination of 0.4% Acid LAC and 0.2% Kem-Gest to nursery pig diets reduced ADFI and pig growth rate. In Exp. 2, pigs fed the acid sequence of Acid LAC-Kem-Gest had similar growth performance to pigs fed carbadox, and this novel dietary acid sequence may have merit as a replacement for antibiotics in the nursery phase.

Key Words: acid • carbadox • Escherichia coli • growth • Salmonella • weanling pig


   INTRODUCTION
Top
 Abstract
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 LITERATURE CITED
 
Newly weaned pigs are susceptible to developing digestive disturbances and gastrointestinal diseases, resulting in stresses on the pig and, consequently, an inability to meet their growth potential. Enterotoxigenic bacteria, in particular Escherichia coli in the small intestine and fermentation of less digestible nutrients of the diet in the large intestine, are deemed responsible for these outbreaks (Hampson, 1994Go). Continuous use of antibiotics at low levels at this crucial time has been recognized to improve feed intake, growth performance, and feed efficiency (Zimmermann, 1986Go; Cromwell et al., 1991Go). However, use of low levels of antibiotics in feed may contribute to the development of antibiotic-resistant pathogens (Mroz et al., 2000Go). For this and other reasons, alternatives to in-feed antibiotics should be sought (Wegener et al., 1998Go).

Lowering buffering capacity, via acidification with organic and inorganic acids and their salts, has been indicated to reduce luminal growth of enterotoxigenic microflora and to enhance weanling pig growth performance (Ravindran and Kornegay, 1993Go; Gabert and Sauer, 1994Go). Little research has investigated the combined use of dietary acids in blends. A blend of acids may be more beneficial than individual acids as a result of a broader spectrum of activity (Namkung et al., 2003Go).

Therefore, the objectives of these studies were to investigate the effects of dietary Acid LAC and Kem-Gest acid blends separately and in combination, along with acid sequencing programs, on weanling pig growth performance. In addition, the effects of dietary acidifiers on microbial populations of the gastrointestinal tract were evaluated using fecal microbial shedding as an indicator of gut health.


   MATERIALS AND METHODS
Top
 Abstract
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 LITERATURE CITED
 
All animals were housed and cared for in accordance with Purdue Animal Care and Use Committee regulations. A total of 480 (Exp. 1, n = 180; Exp. 2, n = 300) weanling pigs with an average weaning age of 18.2 (Exp. 1) or 17.7 d (Exp. 2) were used in two 5-wk experiments to evaluate the effects of supplementing weanling pig diets with Acid LAC or Kem Gest acid blends (Kemin Americas, Des Moines, IA) on growth performance and microbial shedding. Experimental procedures for both experiments were similar except for the dietary treatments.

Dietary Treatments
For Exp. 1, dietary treatments were as follows: 1) negative control-basal diet, (no antibiotics); 2) diet 1 plus 55 ppm carbadox (positive control); 3) diet 1 plus 0.4% Acid LAC (fumaric, lactic, propionic, citric, and benzoic acids; Kemin Americas, Des Moines, IA; 4) diet 1 plus 0.2% Kem-Gest (phosphoric, fumaric, lactic, and citric acids; Kemin Americas, Des Moines, IA); 5) diet 1 plus 0.4% Acid LAC and 0.2% Kem-Gest. In Exp. 2, 6 dietary treatments were fed, with diets 1 through 4 identical to Exp. 1, plus the following 2 additional diets: 5) sequence 1 diet, 0.4% Acid LAC for d 0 to 7 followed by 0.2% Kem-Gest for d 7 to 35; and 6) sequence 2 diet, 0.2% Kem-Gest for d 0 to 7 followed by 0.4% Acid LAC for d 7 to 35. Dietary treatments were made by substituting the treatment products for the basal diet ingredients to maintain isolysinic diets through manipulation of corn and fish meal (phase 1 and 2) or SBM (phase 3), and isocaloric diets through manipulation of soybean oil (phase 1 and 2) or swine grease (phase 3).

Animal and Feeding Management
Pigs were allotted to the treatments based on genetics, sex, and initial BW (Exp. 1, 6.04 kg; Exp. 2, 5.65 kg). Pigs were weighed and feed intake recorded weekly during each 5-wk study. Pigs were housed at 6 (0.28 m2/pig; Exp. 1) or 10 (0.20 m2/pig; Exp. 2) pigs/pen and 6 (Exp.1) or 5 (Exp. 2) pens/treatment. All pigs had unlimited access to feed and water through a 5-hole self feeder and a single nipple waterer in each pen. Pigs were fed in 3 dietary phases, with treatments remaining constant throughout the study (Tables 1Go and 2Go). Phase 1 diets were fed from d 0 to 7, phase 2 diets were fed from d 7 to 21, and phase 3 diets were fed from d 21 to 35. All diets were formulated to meet or exceed the nutrient requirements for their phase of growth based on NRC (1998)Go.


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  		Table 1. Composition of basal (control) nursery pig diets for Exp. 1 and 2, as-fed basis
 

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  		Table 2. Composition of experimental diets (Exp. 1 and 2)1
 
All diets were analyzed for carbadox (Oscar E. Olson Biochemistry Laboratories, Analytical Services Laboratory, South Dakota State University, Brookings, SD), DM, ash, N, P, K, Ca, and pH. Diets were ground through a 1-mm screen in a Wiley mill before analysis. Dry matter was determined after a 12-h drying period at 100°C. A calibrated, glass-electrode pH meter (WTW pH 340, WTW Measurement Systems Inc., Ft. Myers, FL) was used to measure the pH of all samples. Total nitrogen (Nelson and Sommers, 1972Go) was determined by microkjeldahl procedures. Feed total phosphorus was determined colorimetrically (Murphy and Riley, 1962Go) using a Beckman DU-6 spectrophotometer (Beckman Instruments Inc., Irvine, CA). For Ca, P, and K determination, feed samples underwent overnight digestion with 5 mL of concentrated nitric acid. The following morning, 3 mL of concentrated perchloric acid was added to each tube, the tubes were placed on a room-temperature digestion block and heated to 179.4°C for 1 h, and the temperature was then increased to 200°C for an additional 3 h. The tubes were allowed to cool and diluted to 30 mL. Potassium and Ca were determined by atomic absorption spectrophotometry (SpectraAA 220 FS, Varian, Walnut Creek, CA).

Procedures for Microbial Shedding
Fresh fecal samples were collected from 3 pigs/pen on d 6, 20, and 34 for Exp. 1 and on d 32 for Exp. 2 for measurement of pH and plating for E. coli and Salmonella. A calibrated, glass-electrode pH meter (WTW pH 340) was used to measure the pH of the fecal samples, which were diluted with deionized water at a ratio of 1:7.5 (wt:wt). Fecal samples were pooled on an equal weight basis to form a pen composite that was plated for E. coli and Salmonella.

The procedures used for plating E. coli and Salmonella were adapted from Belæil et al. (2004)Go and are as follows: A 1-g subsample of each pen composite fecal sample was mixed into 9 mL of peptone broth, serially diluted with peptone broth, and used to inoculate Mac-Conkey agar plates (Difco Laboratories, Detroit, MI) for E. coli isolation. The E. coli plates were inoculated at 3 dilutions and in triplicate at each dilution. Samples taken after phase 1 were serially diluted by a factor of 105, 106, and 107 and then plated (Exp. 1 and 2). For phases 2 and 3 of Exp. 1, samples were serially diluted by a factor of 104, 105, and 106 and then were plated; for phase 3 of Exp. 2, samples were diluted by a factor of 103, 104, and 105 and then were plated. This change in dilution rate for phase 3 of Exp. 2 was a result of a decrease in bacteria numbers observed in Exp. 1. The MacConkey agar plates were incubated for 24 h at 37°C, and after removal from the incubator, E. coli colonies were immediately determined per plate by counting.

For Salmonella, the serially diluted peptone broth tubes were incubated overnight at 37°C, and 1 mL was transferred to 9 mL of tetrathionate broth (Neogen Corporation, Lansing, MI) and incubated for 48 h at 42°C. From these tubes, 1 mL was used to inoculate 9 mL of Rappaport Vassiliadis broth (Neogen Corporation) and incubated for 48 h at 42°C. The Rappaport broth was used to inoculate XLT4 plates (Neogen Corporation) for Salmonella isolation, and Salmonella was presumptively identified using LIA and TSI agar tubes (Difco Laboratories).

Statistical Analysis
The analyses of data for Exp. 1 and 2 were conducted in a similar manner. For all response criteria, pen was considered the experimental unit. The dietary treatment effect was tested using the residual error term, with initial BW used as a blocking factor. All data were analyzed using the GLM procedure of SAS (SAS Inst. Inc., Cary, NC). Comparison of treatment means was conducted when the dietary treatment effect reached a significance level of P < 0.10 using the Duncan’s procedure, with the P < 0.05 and P < 0.10 levels of significance. Differences in fecal Salmonella (percent positives) were tested using the {chi}2 method in SAS.


   RESULTS
Top
 Abstract
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 LITERATURE CITED
 
Experiment 1
Growth Performance.
During phase 1 (d 0 to 7), the ADG (Table 3Go) of pigs fed the negative control was numerically (P = 0.15) greater than the ADG of pigs fed the carbadox and combination acid treatments (135 vs. 106 and 104 g/d, respectively). During phase 1, pigs fed the negative control had a greater ADFI (P < 0.05) than those fed the carbadox diet, the Acid LAC diet, and the combination acid diet. Although the ADFI for the Acid LAC diet and the Kem-Gest diet were not different from each other, the Kem-Gest fed pigs had greater ADFI (P < 0.05) than the carbadox-fed pigs.


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  		Table 3. The effect of dietary acids on the growth performance of nursery pigs (Exp. 1)1
 
During phase 2 (d 7 to 21), pigs fed the diet containing carbadox and pigs fed the combination acid diet had similar ADG (266 vs. 214 g/d; Table 3Go). The ADFI for pigs fed the combination acid diet was lower (P < 0.05) than the ADFI for all other treatments, with the exception of the Kem-Gest diet, which tended (P < 0.10) also to be greater than the combination diet. There were no differences among treatments for feed efficiency during phase 2 or d 21 BW. Dietary treatment had no effect on ADG and ADFI during the third phase of the study (d 21 to 35). Feed efficiency tended (P < 0.10) to be better for pigs fed the carbadox diet compared with pigs fed the negative control diet and the Kem-Gest diet. There were no differences in BW at d 35 among dietary treatments.

Over the 5-wk study there were no effects of dietary treatment on any growth performance parameters measured. Overall, ADFI for pigs fed the combination acid diet was numerically (P = 0.26) lower than the ADFI of pigs fed all other dietary treatments (Table 3Go).

Bacteria Concentration.
Concentrations of E. coli and prevalence of Salmonella from preweaning pigs were 8.62 log10 for E. coli, and 1 litter out of 24 sampled was positive for Salmonella. On d 6, pigs fed the negative control diet had lower E. coli concentrations (Table 4Go) than pigs fed any of the other dietary treatments (P < 0.05). The presence of an unidentified organism on the E. coli plates was documented at this time point, and this bacterium was only present in pigs that were being fed the negative control diet. However, the identity of this bacterium is not known.


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  		Table 4. The effect of dietary acids on fecal Escherichia coli and Salmonella shedding and fecal pH of nursery pigs (Exp. 1)1
 
There was no effect of dietary treatment on the presence of Salmonella. There were no Salmonella present in any pens sampled that were fed either the Kem-Gest diet or the combination acid diet on d 6 of the study. It was noted that 33.3% of pens fed the Acid LAC diet were positive for Salmonella and 16.7% of pens fed the negative control and the carbadox diets were positive for Salmonella on d 6 of the experiment.

Samples taken on d 20 indicated that pigs fed the negative control diet had numerically greater E. coli colonies being shed than pigs on any of the other dietary treatments; however, there were no statistical differences among treatments at this time. Unidentified organisms were present in all the acid diets at this time point but not in the negative or positive controls. There were no statistical differences among treatments for these bacteria. On d 20, 16.7% of pens fed the antibiotic diet and the Acid LAC diets were found to be positive for Salmonella, but there were no differences among treatments.

On d 34, E. coli concentrations in pigs being fed the carbadox diet were greater (P < 0.05) than pigs fed the combination acid diet. Also, pigs fed the combination acid diet and the Acid LAC diet tended (P < 0.10) to have lower E. coli fecal shedding than pigs fed the positive and negative control diets with the Kem-Gest diet being intermediate. On d 34, the unidentified bacterium was present in pigs on all dietary treatments with the exception of the negative control diet (P < 0.05). On d 34, 16.7% of pens fed the antibiotic diet and the Acid LAC diet were found to be positive for Salmonella, which coincides with what was observed on d 20 of the experiment. However, there were no differences in the presence of Salmonella among treatments.

Fecal pH.
The fecal pH (Table 4Go) of pigs fed the combination acid diet was numerically greater than pigs fed all other dietary treatments in particular the Acid LAC diet or the Kem-Gest diet (7.01 vs. 6.65 and 6.63) on d 6.

Experiment 2
Growth Performance.
Throughout phase 1 of the study (d 0 to 7), there was no effect (P > 0.05) of dietary treatment on ADG, ADFI, G:F, or d 7 BW (Table 5Go).


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  		Table 5. The effects of dietary acids and their feeding sequences on the growth performance of nursery pigs (Exp. 2)1
 
During phase 2 of the study (d 7 to 21), ADG of pigs fed the carbadox diet was similar to the ADG of pigs fed the acid sequence 1 diet. Both of these treatments tended to be greater than the ADG of pigs on all other treatments (P < 0.10), with the exception of the sequence 2 treatment, which was intermediate. Pigs fed the sequence 1 diet had the highest ADFI during phase 2, which was similar to the ADFI of pigs fed the carbadox diet. The ADFI of pigs fed the sequence 1 treatment was greater than the ADFI of pigs being fed the sequence 2 treatment (P < 0.05) and tended to be greater than the ADFI of pigs fed the Acid LAC treatment (P < 0.10). Pigs fed the carbadox diet tended (P < 0.10) to have greater ADFI than pigs fed the Acid LAC and sequence 2 treatments. There was no effect of dietary treatment on pig G:F during this time period. On d 21, pigs fed the sequence 1 diet had the heaviest BW and the greatest numerical difference in BW was between the sequence 1-fed pigs and the pigs fed the Acid LAC diet.

Pigs fed the carbadox diet had greater phase 3 (d 21 to 35) ADG (P < 0.05) than pigs fed all other dietary treatments, with the exception of pigs fed the sequence 1 diet, which had similar ADG to pigs fed the carbadox diet. Pigs fed the sequence 1 diet also had greater ADG (P < 0.05) than pigs fed the other acid treatments and tended to have greater ADG (P < 0.10) than the negative control. Pigs fed the sequence 1 diet and the carbadox diet had similar ADFI during this time period, and both of these treatments had greater ADFI than pigs fed the sequence 2 diet and the Kem-Gest diet (P < 0.05). In addition, they both tended to have greater ADFI (P < 0.10) than pigs fed the Acid LAC treatment. Pigs fed the negative control diet had greater ADFI (P < 0.05) than pigs fed the sequence 2 diet. The G:F of pigs was not affected by dietary treatment. On d 35, pigs fed the sequence 1 diet and the carbadox diet tended to have heavier BW than pigs on any other treatment (P < 0.10).

Overall, pigs fed the carbadox diet and the sequence 1 diet had greater ADG than all other treatment groups (P < 0.05). The ADFI of these 2 groups was also greater than all other acid treatment groups (P < 0.05) and tended to be greater than pigs fed the negative control diet (P < 0.10).

Bacteria Concentrations.
Escherichia coli and Salmonella shedding was determined from fecal samples taken on d 32 of the study, and there were no differences among treatments at this time point among dietary treatments (Table 6Go). The presence of an unidentified bacterium was also quantified at this time, but there were no differences in the amount of this bacteria shed among dietary treatments. The presence of Salmonella was only noted in pens fed the sequence 2 diet and the negative control diet. In each of these treatment groups there was a 20% positive occurrence for Salmonella.


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  		Table 6. The effect of dietary acids on fecal E. coli and Salmonella shedding and fecal pH of nursery pigs (Exp. 2)1
 
Fecal pH.
In Exp. 2, fecal pH of pigs fed sequence 1 tended to be greater than fecal pH of pigs fed negative control, Kem-Gest, and sequence 2 (P < 0.10).


   DISCUSSION
Top
 Abstract
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
LITERATURE CITED
 
The objective of these studies was to evaluate performance of Acid LAC and Kem-Gest acid blends individually, in combination, and in sequence in nursery pig feeding programs as potential alternatives to antibiotic growth promoters. Although antibiotics help ensure a control of diarrhea outbreaks and mortality caused by bacterial infections in pigs, a risk of developing cross-resistance of pathogens to antibiotics used in human medicine has become more evident and is of public concern (Piva, 1998Go; Hillman, 2001Go). As a result, the swine industry is now searching for an equally competent, if not superior, alternative to antibiotics in relation to growth performance and health in nursery pig diets.

Results from these studies demonstrate that the overall growth performance of nursery pigs may be enhanced by the addition of growth-promoting agents in their diets. Inclusion of antibiotic growth promoters to the diet can increase growth performance of nursery pigs over diets containing no antibiotics (Zimmermann, 1986Go; Yen and Pond, 1987Go; Cromwell et al., 1991Go). In concurrence with previous results, the overall growth performance of pigs in Exp. 2 was greater for pigs fed diets containing carbadox compared with pigs not receiving an antibiotic. However, in Exp. 1, addition of carbadox to the diet did not affect growth rate. This unexpected event may have been a result of the abrupt change in diet coupled with a poor acclimation period postweaning by these pigs, which has been shown to adversely affect growth performance of newly weaned pigs (Aumaître et al., 1995Go; Cranwell, 1995Go; Jahn and Uecker, 1997Go). The lack of a growth response to an antibiotic in Exp. 1 may also be a result of pigs having a high health status entering the nursery. Pigs in Exp. 1 had greater ADG compared with pigs in Exp. 2.

In Exp. 2, growth performance of pigs fed the acid sequence 1 treatment, which was comprised of 0.4% Acid LAC for the first 7 d followed by 0.2% Kem-Gest for the following 28 d, was similar to that of pigs fed the carbadox diet and was significantly greater than for pigs on all other acid treatments. Possible explanations for success of the sequence 1 treatment above that of individual dietary acid blends on their own or the reverse sequence may lie in the ability of organic acids to exert their most beneficial effects in the first 2 wk postweaning. Radecki et al. (1988)Go noted that fumaric acid improved ADG of weanling pigs during the first 2 wk postweaning, however, over a 4-wk period there was no effect. Kirchgessner and Roth (1987)Go reported that the effects of sodium formate were greater immediately postweaning. Similar results were reported by Giesting et al. (1991)Go and support the hypothesis that young weanling pigs may be unable to adequately digest certain nutrients due to a lack of HCl secretion and protease activation at this time.

Inclusion of organic acids in the postweaning diet enables the weanling pig to overcome these nutritional obstacles; however, their effectiveness appears to diminish as the pig’s digestive system matures. Another possible reason why the acid sequence 1 treatment was superior to the acid sequence 2 treatment may be the order in which the acids were fed. During phase 1, pigs fed diets containing Acid LAC had greater ADFI than pigs fed diets containing Kem-Gest. However, feed intake was suppressed by Acid LAC during phase 2, and both acids reduced feed intake in phase 3. The greater inclusion rate of acid in the Acid LAC diet may have also contributed (0.4 vs. 0.2%) to the reduced growth performance and feed intake during phase 2 and 3. These results are in agreement with work by Radecki et al. (1988)Go who noted that the addition of citric acid at high levels had a negative effect on feed intake. Levels of acids fed in the current experiments are lower than many reported in the literature. However, most inclusion levels reported in the literature are for individual organic acids, and the inclusion of a mixture of a number of different acids together may increase their potency and possibly decrease the palatability of the diet. Additionally, feeding Acid LAC for the first 7 d in Exp. 2 may help to establish beneficial bacterial populations such as lactobacillus (Cole et al., 1968Go; Roth and Kirchgessner, 1997Go; Maribo et al., 2000Go). Additional sequencing with Kem-Gest during phases 2 and 3 may then help reduce E. coli populations (Bolduan et al., 1988Go; Jørgensen et al., 2002Go; Biagi et al., 2003Go) and assist with the digestion of a simpler diet containing more corn and soybean meal in phases 2 and 3 compared with a more complex milk product based diet fed during phase 1 (Burnell et al., 1988Go; Giesting et al., 1991Go).

Performances of pigs fed the Acid LAC or Kem-Gest diet on their own were similar to each other in both experiments. In Exp. 2 growth performance for acid sequence 1 was similar to carbadox-fed pigs and significantly better than the pigs that received no growth-promoting additives in their diets. However, in Exp. 1 there were no overall benefits in relation to growth. The reason for this may be related to the overall health status of the pigs. Pigs in Exp. 1 grew faster than pigs in Exp. 2, indicating that there may have been more disease pressure in Exp. 2.

As early as 1968, Cole et al. observed a reduction in E. coli concentrations in pigs receiving dietary acidifiers. This work was supported by Thomlinson and Lawrence (1981)Go who observed a reduction in the multiplication of E. coli O141:K85 and consequently a reduction in piglet mortality as a result of acidification. However, in these experiments, none of the dietary treatments resulted in a reduction in E. coli compared with pigs fed the negative control diet. In both Exp. 1 and 2, the presence of an unidentified bacterium was quantified from E. coli plates. Our results lead us to believe that there may be a competitive exclusion relationship between E. coli and these unidentified bacteria. When the population of E. coli numerically decreased, the population of the unidentified bacteria increased. It is possible that these bacteria are indigenous to the gastrointestinal tract and undergo a period of proliferation following the removal of their major competitors. Such intestinal bacteria may be beneficial to the host animal by further preventing colonization of the intestine by pathogenic organisms by competing more successfully for nutrients or for epithelial attachment sites (Rolfe, 1997Go). Further research is needed to identify this bacteria and the possible relationship with E. coli and pig health.

Results from Exp. 1 suggest that the presence of Salmonella is unaffected by the dietary treatments used. Salmonella was consistently found in pens fed the carbadox diet and also the Acid LAC diet throughout the trial. However, this is most likely due to initial Salmonella infection during the nursing period of lactation and was not eliminated during the postweaning nursery period. In Exp. 1, fecal pH decreased over the course of the trial. However, the fecal pH of pigs fed different dietary treatments were not statistically different from each other. As the pig’s gastrointestinal tract matures, it becomes more competent in the production of hydrochloric acid (Kidder and Manners, 1978Go). This would account for the overall reduction in fecal pH from 6 to 20 d postweaning. However, dietary acids function in the upper portion of the gastrointestinal tract, so alterations in fecal pH are seldom observed. Scipioni et al. (1978)Go reported a decreased duodenal pH when citric acid was added to the diet. Likewise, Burnell et al. (1988)Go observed a lowering of intestinal pH when citric acid was included in the diet at a level of 1%.

Use of Acid LAC and Kem-Gest (Exp.1) in nursery pig diets resulted in similar growth rates, feed intakes, and feed efficiency compared with the negative control diet and the carbadox containing diet. However, a sequencing program (Exp. 2) produced growth performance similar to carbadox and better than the negative control diet. Therefore, sequencing dietary acidifiers in the nursery may be a viable alternative to antibiotic use. However, as seen in Exp. 1, feeding too high a level of an acid blend (0.6%) may result in reduced feed intake and poor growth. The positive response obtained by feeding a sequence of Acid LAC followed by Kem-Gest is very promising but requires further validation.


   Footnotes
 
1 ARP # 2005-17706. Back

2 Financial support provided in part by Kemin Americas Inc., Des Moines, IA. Back

3 Current address: International Nutrition, Omaha, NE. Back

4 Corresponding author: brichert{at}purdue.edu

Received for publication November 1, 2005. Accepted for publication June 5, 2006.


   LITERATURE CITED
Top
 Abstract
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 LITERATURE CITED
 


Aumaître, A., J. Peiniau, and F. Madec. 1995. Digestive adaptation after weaning and nutritional consequences in the piglet. Pig News Inf. 16:73N–79N.

Belæil, P. A., C. Chauvin, K. Proux, F. Madec, P. Fravalo, and A. Alioum. 2004. Impact of the Salmonella status of market-age pigs and the pre-slaughter process on Salmonella caecal contamination at slaughter. Vet. Res. 35:513–530.[CrossRef][Medline]

Biagi, G., A. Piva, T. Hill, D. K. Schneider, and T. D. Crenshaw. 2003. Low buffering capacity diets with added organic acids as a substitute for antibiotics in diets for weaned pigs. Proc. 9th Int. Symp. Dig. Physiol. Pig. 2:217–219. Univ. Alberta, Edmonton, Alberta, Canada.

Bolduan, G., H. Jung, R. Schneider, J. Block, and B. Klenke. 1988. Influence of fumaric acid and propanediol formate on piglets. J. Anim. Physiol. Anim. Nutr. (Berl.) 59:143–149.

Burnell, T. W., G. L. Cromwell, and T. S. Stahly. 1988. Effects of dried whey and copper sulfate on the growth responses to organic acid in diets for weanling pigs. J. Anim. Sci. 66:1100–1108.[Abstract/Free Full Text]

Cole, D. J. A., R. M. Beal, and J. R. Luscombe. 1968. The effect on performance and bacterial flora of lactic acid, propionic acid, calcium propionate and calcium acrylate in the drinking water of weaned pigs. Vet. Rec. 83:459–464.[Medline]

Cranwell, P. D. 1995. Development of the neo-natal gut and enzyme systems. In The Neonatal Pig, Development and Survival. M. A. Varley, ed. CAB Int., Wallingford, Oxon, UK.

Cromwell, G. L., T. S. Stahly, K. A. Dawson, J. J. Monegue, and K. Newman. 1991. Probiotics and antibacterial agents for weanling pigs. J. Anim. Sci. 69(Suppl. 1):114. (Abstr.)

Gabert, V. M., and W. C. Sauer. 1994. The effect of supplementing diets for weanling pigs with organic acids. A review. J. Anim. Feed Sci. 3:37–87.

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