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* Department of Animal Science and Interdepartmental Nutrition Program, North Carolina State University, Raleigh 27695-7621 and
and
Cape Fear Consulting, LLC, Warsaw, NC 28398
2 Correspondence:
Box 7621 (phone: 919-513-1116; fax: 919-515-6316; E-mail:
Eric_vanHeugten{at}ncsu.edu).
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResultsDiscussionImplicationsLiterature Cited |
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Key Words: Antibiotics • Copper • Growth • Pigs • Yeasts • Zinc
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Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionImplicationsLiterature Cited |
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The objective of these studies was: 1) to evaluate the effects of live yeast on nursery pig performance, nutrient digestibility, and fecal microflora in pigs fed diets with two different carbohydrate sources and 2) to determine the effects of yeast supplementation to diets with or without antibiotics and growth-promoting concentrations of Zn and Cu on nursery pig performance and fecal microflora.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionImplicationsLiterature Cited |
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Experiment 1
One hundred fifty-six crossbred ([Landrace x Yorkshire] x [Hampshire x Duroc]) pigs were weaned at 17 d of age (initial BW = 5.9 kg), blocked by weight, and allotted to one of four dietary treatments based on BW and litter origin. When pigs of the same litter were allocated to the same pen, pigs were switched within block to ensure that littermates were distributed across treatments as much as possible. Treatments were arranged in a 2 x 2 factorial randomized complete block design and factors consisted of: 1) dietary supplementation with oat products (oat flour and steam-rolled oats; 0 or 27.7%), and 2) yeast supplementation at 0 or 1.6 x 107 cfu/g of feed (BIOSAF, Saf Agri, Minneapolis, MN). The yeast source consisted of a concentrate of live Saccharomyces cerevisiae SC47 and contained at least 8 x 109 live cells/g.
Pigs were housed six or seven pigs per pen in two environmentally controlled nursery rooms with 12 pens (1.83 x 1.52 m) each, resulting in six replicates per treatment (39 pigs per treatment). Temperature in the nursery was initially 27°C and was lowered by 1°C each week. Pigs were fed a complex prestarter diet for 2 wk, a starter I diet for 2 wk, and a starter II diet for 2 wk (Table 1
). The basal prestarter diet was the only diet with significant levels of oat products and the aforementioned treatments were applied. Because the starter I and II diets did not contain oat products, there were only two dietary treatments in the starter phases (control vs. yeast). However, pigs were not reallotted to evaluate possible carryover effects from the prestarter treatments. Prestarter, starter I, and starter II diets were formulated to meet or exceed NRC (1998) nutrient requirements and contained 1.6, 1.4, and 1.25% total lysine, respectively. Concentrations of other amino acids (methionine, threonine, and tryptophan) were kept constant at ratios suggested by Baker and Chung (1992). Feed and water were freely available throughout the study. Pig BW and feed consumption were measured weekly for the 6-wk experimental period.
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Fecal samples for digestibility measurements were dried at 60°C and subsequently ground through a 1-mm screen in a Retsch grinder (model ZM 100, Irvine, CA). Dry matter, fat (ether extract), and CP (Kjeldahl N x 6.25) analysis were conducted according to AOAC (1997) procedures. Phosphorus concentrations were analyzed colorimetrically using the vanadomolybdate procedure (AOAC, 1997). Gross energy was determined by adiabatic bomb calorimetry (model 5001, IKA Works, Wilmington, NC). Analysis of Cr was conducted by wet ashing 2 g of sample with 10 mL of nitric acid and 7 mL of perchloric acid (AOAC, 1997). Chromium was determined with an atomic absorption spectophotometer (model 5000, Perkin-Elmer, Shelton, CT).
For microbial analysis, a 5-g sample was weighed into another whirl pack bag and diluted to a concentration of 1:10,000 (weight:volume) using PBS. Using a spiral-plating machine, the sample was applied to various plates at dilutions of 10-4 to 10-7. The concentration of coliforms present in feces was determined using eosin methylene blue agar (Becton Dickinson, Cockeysville, MD), which is recommended for the detection of gram-negative intestinal pathogenic bacteria. Escherichia coli typically appear as blue-black colonies with dark centers and a green metallic sheen. However, no further confirmatory tests were conducted to identify specific organisms, and therefore, results were reported as coliforms. The concentration of lactobacilli was determined using Lactobacillus selection agar (Becton Dickinson), which is a selective medium for the isolation and enumeration of oral and fecal lactobacilli. Lactobacilli appeared as large white colonies. Total anaerobic bacterial counts were determined using tryptic soy agar (Becton Dickinson). All plates were stored anaerobically at 32°C for 48 to 72 h. Anaerobic conditions were generated using an anaerobic jar with a gas generator envelope (GasPak Plus, disposable H2 and CO2 generating system with palladium catalyst; Fisher Scientific, Pittsburgh, PA). The final anaerobic atmosphere consisted of 6.5 to 7.5% CO2, 25 to 35% H2, with the balance being N2. Yeast counts were determined by pipetting 0.5 mL of the 1:10,000 fecal dilutions onto plates containing potato dextrose agar (Becton Dickinson) and were distributed throughout the plate using the hockey-stick method. The potato dextrose agar was acidified prior to use to inhibit bacterial growth by addition of sterile tartaric acid (10% solution) until a pH of 3.5 was reached. The yeast plates were stored anaerobically at room temperature for 3 d and yeast colonies were identified and counted as white, creamy, and smooth colonies.
Yeast concentrations in the feed were determined by a commercial laboratory (Covance Laboratories, Madison, WI). A 30-g feed sample was mixed with 40 to 50 mL of sterile distilled water (heated to 37°C) and homogenized in a Waring blender. Samples were incubated at 37°C for 15 min without stirring followed by 15 min with stirring. The mixture was then adjusted to a 100-mL volume, mixed, and 10-fold serial dilutions were made ranging from 10 mg/mL to 10-6 mg/mL. One milliliter of each suspension was inoculated onto yeast malt agar containing 1% oxytetracycline and 0.1% chloramphenicol in Petri dishes. Plates were incubated for 48 to 72 h at 30°C, and viable yeast cells/g sample were determined from dilutions containing 30 to 300 colonies per plate.
Experiment 2
Ninety-six pigs ([Landrace x Yorkshire] x [Hampshire x Duroc]) were weaned at 17 d of age, blocked by weight and sex, and allotted to one of four dietary treatments, while distributing littermates across treatments as much as possible. Pigs were housed four pigs per pen, using a total of 24 pens (0.91 x 1.52 m). Treatments were arranged according to a 2 x 2 factorial randomized complete block design with factors: 1) diet type (positive control diet containing growth promoting concentrations of Zn, Cu, and antibiotics or negative control) and 2) live yeast (Saccharomyces cerevisiae SC47) supplementation (0 or 2.4 x 107 cfu/g, BIOSAF, Saf Agri). Management was the same as in Exp. 1, with the exception that the nursery was not cleaned prior to the experiment to provide a more challenging environment to the pigs. Pigs were fed three diet phases (prestarter, starter I, and starter II) for 2 wk each (Table 2). Pig weights and feed consumption were measured on a weekly basis for 6 wk.
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Statistical Analyses
Data were analyzed as a 2 x 2 factorial, randomized complete block design using the GLM procedure of SAS (SAS Inst., Inc., Cary, NC). The model included the effects of block, diet type, yeast supplementation, and the interactive effects of diet type and yeast supplementation. Initial weight was used as a covariate in the analysis of growth performance data in Exp. 1. Pen served as the experimental unit in both experiments. Bacterial and yeast concentrations were transformed (log10) before statistical analysis. Least squares means are presented and considered statistically significant at P < 0.05.
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Results |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionImplicationsLiterature Cited |
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The live yeast product used in Exp. 1 was determined to contain 6 x 109 cfu/g. Based on the inclusion level of 0.20%, the final diets should have contained 1.2 x 107 cfu yeast/g. Analyzed live yeast cell counts were approximately 1.0 x 106 cfu yeast/g in the final diets.
No interactions (P = 0.30) between yeast supplementation and oat products inclusion were observed (Table 3). The addition of yeast to diets with a less digestible energy source (i.e., a greater level of corn rather than oat product) did not appear to improve pig performance. The inclusion of oat product to the diet during the prestarter phase tended (P < 0.10) to reduce feed intake during starter phase I and tended (P < 0.10) to reduce ADG over the entire study, resulting in lower final BW for pigs fed oat products for the first 2 wk after weaning. Live yeast supplementation did not affect growth performance of pigs (P = 0.65).
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). During the starter phase, the number of lactobacilli were reduced (P < 0.05) in feces from pigs fed diets with oat products when yeast was supplemented; however, yeast supplementation to diets without oat products did not affect lactobacilli counts (interaction, P < 0.05). Supplementation of yeast alone resulted in a greater yeast count in fecal samples of pigs during the starter phase (P < 0.05).
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). Similarly, the digestibility of DM (P < 0.10), fat (P < 0.10), P (P < 0.05), and energy (P < 0.10) tended to be lower in the starter phase when pigs were fed diets supplemented with yeast. The inclusion of oat flour and steam-rolled oats in the diet resulted in an improvement in the digestibility of DM (P < 0.001), protein (P < 0.001), fat (P < 0.01), and energy (P < 0.05) in the prestarter phase. As expected, there were no carryover effects of oat products inclusion during the prestarter on nutrient digestibility measured during the starter phase.
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Yeast cell counts in the feed were determined in starter I and II diets before and after pelleting to determine if the proper level of live yeast was added to the diet and if the yeast survived pelleting. Yeast counts were 2.1 x 107 and 2.7 x 107 cfu/g of pelleted feed for the starter I and II diets, respectively, and were in reasonable agreement with the targeted inclusion rate of 2.4 x 107 cfu/g of feed. Yeast counts in the pelleted feeds were 97 and 95% of those in the meal feeds (before pelleting) for the starter I and starter II diets, respectively, indicating that yeast survived pelleting at 60°C.
As part of standard operating procedures, several pigs were treated with injectable antibiotics because they appeared unthrifty, and one pig was treated for a swollen joint. The total number of days that pigs were treated (number of pigs x days) with antibiotics was 14, 3, 0, and 3 for the positive control diet, the positive control diet with yeast, the negative control diet, and the negative control diet with yeast, respectively. Interactive effects on body weights were observed (P < 0.001) between diet type and yeast supplementation (Table 6). Pigs fed diets that contained growth-promoting concentrations of Zn, Cu, and antibiotics and were supplemented with yeast were 2.12 kg heavier (P < 0.001) at the end of the experimental period compared with pigs not supplemented with yeast. Supplementation of yeast to the negative control diets did not improve final weights of pigs (P = 0.80). Average daily gain during starter phase I (P < 0.02), starter phase II (P < 0.02), and overall (P < 0.01) was greater for pigs receiving yeast supplementation in positive control diets compared with those not receiving yeast. However, supplementation of yeast to negative control diets did not affect daily gain. The improvement in daily gain observed in pigs fed the positive control diets with yeast was partly related to increased feed intake in those pigs during starter phase I (P < 0.01) and a tendency for improved intake for the entire experimental period (P < 0.10). Addition of Zn, Cu, and antibiotics to the diet resulted in an improvement in feed efficiency during the prestarter period (P < 0.02) and tended to improve feed efficiency during the starter I phase and overall (P = 0.10).
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). Pigs fed diets without growth-promoting concentrations of Zn, Cu, and antibiotics tended to have lower counts of lactobacilli and coliforms than pigs fed the positive control diets (P < 0.05). Yeast counts tended to be lower in pigs fed the positive control diet containing yeast compared with pigs fed the positive control diet without yeast, but were not different when yeast was supplemented to the negative control diets (interaction, P < 0.10).
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Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionImplicationsLiterature Cited |
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Supplementation of live yeast or yeast culture has been reported to improve growth performance in weanling pigs (Veum et al., 1988; Jurgens et al., 1997; Maloney et al., 1998; Mathew et al., 1998). However, results have been variable, and others have reported no benefit of yeast supplementation (Jurgens, 1995; Kornegay et al., 1995). Differences in yeast products that are available on the market should be noted. Active dry yeast is defined as yeast that has been dried to preserve its fermenting power and must contain at least 15 x 109 live yeast cells per gram (AAFCO, 2002). Dried yeast is defined as dried nonfermentative yeast separated from its medium and must contain at least 40% CP. Yeast culture is yeast and the media on which it was grown, dried to preserve its fermenting power (AAFCO, 2002). The live yeast product used in the present study was guaranteed to contain at least 8 x 109 live yeast cells per gram of product.
Performance of pigs was not affected by yeast supplementation in Exp. 1. In contrast, in Exp. 2, supplementation of weanling pigs with yeast improved pig performance, particularly when pigs were fed diets containing antimicrobial agents. Differences in results between the two experiments may be due to several factors. First, the level of live yeast present in the diets varied between Exp. 1 and 2. The analyzed concentration of live yeast in Exp. 1 was much lower than the concentration in Exp. 2. Thus, the concentration of live yeast in Exp. 1 may have been too low to elicit a positive response. The exact level of yeast required to improve pig performance has not been clearly defined. Second, the level of sanitation employed in the nurseries was different. Pigs were housed in clean nursery rooms in Exp. 1, whereas rooms had not been cleaned or disinfected in Exp. 2. The response to antimicrobial agents has been reported to be greater in a "dirty" environment (Cromwell, 2000), and we observed a positive response from antibiotic supplementation in the present experiment. We hypothesized that yeast supplementation in pigs housed in a challenging environment could replace the need for the use of antimicrobial concentrations of Zn, Cu, and antibiotics. However, yeast appeared to work in concert with the other growth promotants used in Exp. 2 and did not affect pig growth performance when supplemented to diets without growth-promoting concentrations of Zn, Cu, and antibiotics. When comparing pig performance between Exp. 1 and 2, it appears that pigs gained at a lower rate and consumed less feed during the prestarter phase in Exp. 2 (unclean environment) than Exp. 1, but performance was superior in Exp. 2 for the remainder of the trial duration. Although other factors may have impacted pig performance, and a direct comparison between experiments cannot be made, it appears that our challenge environment was only marginally effective during the prestarter phase, but not overall. Thus, it is not clear whether sanitary conditions in the nursery were responsible for differences in results between the two trials. The third difference between the two experiments was the type of antibiotic, which may have altered the response of pigs to yeast supplementation.
Positive effects of antibiotic use in pigs have been clearly documented, although the mechanism of action remains unclear (Anderson et al., 1999). It has been suggested that antibiotics may allow for more efficient intestinal growth and may reduce growth-depressing microbial metabolites, subclinical infections, and competition for nutrients by microorganisms through modification of the gut microflora, and therefore, improve growth rate (Visek, 1978; Anderson et al., 1999). We observed increased fecal lactobacilli and coliform counts in pigs fed diets supplemented with antibiotics and high levels of Cu compared with negative control diets, which is in contrast to the expected antimicrobial effects of Cu and antibiotics. Diets fed during the time fecal collections were made contained tylosin, which largely affects gram-positive bacteria and sulfamethazine, which is a broad-spectrum antibiotic (Henry and Apley, 1999). Although the microbial populations that we measured did not decrease, we observed improved pig performance when antimicrobial agents were included in the diet. Similar to the proposed action of antibiotics, the use of yeast can potentially alter gut microflora by selectively stimulating growth of beneficial bacteria while suppressing the growth of pathogenic bacteria. In the present experiment, yeast supplementation had limited effects on microbial counts in fresh feces. Mathew et al. (1998) reported no differences in the microflora in the stomach, duodenum, ileum, cecum, or colon of pigs supplemented with live yeast. Although the evaluation of populations of bacteria in the gut can be helpful in determining the activity of yeast supplementation, a more detailed analysis of specific microbial species and how they are affected by dietary supplementation is needed to fully understand the impact of gut microflora on animal health and performance (Anderson et al., 1999).
Steam-rolled oat groats are often included in diets for weanling pigs because of their high digestibility. Indeed, the present study indicates that DM, CP, fat, and GE digestibility of diets with oat products was superior to the digestibility of diets containing corn as the main energy source. In spite of improved digestibility, pig performance was not affected by oat product inclusion and appeared to negatively affect ADFI and overall ADG. It should be noted that oat products were included only during the prestarter phase of the experiment, and thus it appears that effects on performance were due to carryover effects. Improvements in pig performance due to increased digestibility of oat products may not be expected in the current experiment because diets were formulated to meet or exceed nutrient requirements. In contrast to our observations, Rantanen et al. (1995) reported no differences in performance of pigs fed different oat products. Supplementation with live yeast did not affect growth performance, regardless of whether oat products were included in the diet or not. Studies with ruminants and horses have demonstrated positive effects of yeast supplementation on N metabolism and fiber digestion (Glade and Biesik, 1986; Wiedmeier et al., 1987; Cole et al., 1992). Kornegay (1995) observed no effects of supplementation with yeast culture on performance or nutrient digestibility in pigs fed different fiber sources. In the present study (Exp. 1), supplementation of live yeast resulted in decreased digestibility of DM, fat, and GE in prestarter and starter pigs without affecting growth performance. Digestibility measurements were made at the fecal level, and therefore, calculations include disappearance of nutrients through absorption and bacterial assimilation of nutrients in the small and large intestine. Canh et al. (1997) demonstrated that N digestibility decreased with the inclusion of sugar beet pulp in the diet, which may be due to enhanced bacterial fermentation in the hindgut and a subsequent shift of N excretion from urine to feces. However, in the current experiment, digestibility of CP was not affected by yeast supplementation. In addition, Mathew et al. (1998) did not observe any effects of live yeast supplementation on microfloral concentrations or volatile fatty acid concentrations (as an indicator of microbial activity) along the gastrointestinal tract of weanling pigs.
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Implications |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionImplicationsLiterature Cited |
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Footnotes |
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3 Present address: Dept. of Anim. Sci., Colorado State University, Fort Collins.
Received for publication July 30, 2002. Accepted for publication November 26, 2002.
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Literature Cited |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionImplicationsLiterature Cited |
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