Table 1.
Effects of different types of feed additives on gut health and performance of young pigs.
| Additive Type | Composition | Age of Piglets/Experiment Duration | Dose | Intestinal Structure, Gut/Health Microbiota | Performance/Other Observations | References |
|---|---|---|---|---|---|---|
| Fatty acid (FA) | ||||||
| Medium-chain fatty acid | Caprylic or capric acid | 32 days old/49-d trial | 2 g/kg | Reduced Clostridium perfringens levels;improved mucosal epithelium structure of ileum | Improved overall ADG. FCR in pigs receiving diet supplemented with caprylic acid was better; increased digestibility and reduced mortality | [53] |
| Poly unsaturated fatty acids | Coated n-3 FA | 28 days old/42-d trial | 5, 10 and 15 g/kg. | Trends in linear increment in fecal Lactobacillus counts at weeks 3 and 6 | Linear increase in ADG during week 1, 3 and overall, G:F linearly increased during overall; linear increase in DM and N digestibility at the end of experiment | [54] |
| Nucleotides | ||||||
| UMP, GMP, AMP, CMP, and IMP | 19 days old/21-d trial | 0, 50, 150, 250, and 500 mg/kg | Quadratic response on villus height–crypt ratio, linear reduction in crypt cell proliferation in jejunum, reduced jejunal IL-6 when nucleotide increased from 50 to 150 mg/kg | Increased ADG during the first 11 days when pigs received diet supplemented with 50–150 mg/kg nucleotide | [55] | |
| UMP/UR | 12 days old/10-d trail | 476 mg UP, 348 mg UR(orally) | Decreased the diarrhea rate, UR increased the jejunum villus length/crypt depth ratio, Claudin-3, and E-cadherin expression, and the pyrimidine nucleotide metabolic enzymes in the duodenal mucosa, UMP and UR decreased the expression of CAD and RRM2 at the jejunal mucosa | UMP and UR supplements improved the ADG of piglets | [56] | |
| UMP, GMP, AMP, CMP, and IMP | 28 days old/28-d trial | 0.8 g/head/day | No differences in gene expression levels of inflammatory cytokines (IL1α, IL1β, IL6, IL10, TNFα, TLR2, TLR4, and PPAR) at ileal Peyer’s patches level; no effect on IgA and IgG content in blood | Increased BW and ADG but not G:F | [57] | |
| Organic acid (OA) | ||||||
| Pure OA (propionic acid, lactic acid, formic acid, malic acid, citric acid, or fumaric acid) | 25 days old/28-d trial | 10, 16, 12, 12, 15, and 15 g/kg, respectively | Reduced incidence and severity of diarrhea | Heavier BW, and increased ADG and FI especially with lactic acid supplementation | [58] | |
| Formic acid | 35 days old/42-d trial | 0, 1.4 g/kg (low formic acid; LFA), or 6.4 g/kg (high formic acid; HFA) | Increased microbiota diversity in high FA group | Increased ADG, ADFI and improved feed efficiency during the first three weeks in both high and low OA group | [59] | |
| 17% fumaric acid, 13% citric acid, 10% malic acid, and 1.2% medium-chain fatty acid (protected OA) | 28 days old/42-d trial | 1 and 2 g/kg | Reduction in E. coli counts at week 3 and increase in Lactobacillus counts in week 6 with 2 g/kg organic acid | Increased overall ADG and ADFI | [60] | |
| Formic acid, acetic acid, and propionic acid combined with medium chain fatty acids | 28-d trial | 3 g/kg | Reduced the incidence of diarrhea and fecal E. coli counts, the ratio of villus height-to-crypt depth in the jejunum and ileum was higher | Digestibility of dry matter, total carbohydrates, NDF, and ADF was increased during days 14–28 | [61] | |
| 17% fumaric acid, 13% citric acid, 10% malic acid, and 1.2% medium-chain fatty acid | 28 days old/42-d trial | 0, 1, and 2 g/kg | Linear increase in fecal Lactobacillus counts and linear reduction in E. coli and Salmonella counts | Increase in overall ADG and DM digestibility | [62] | |
| Prebiotics | ||||||
| Fructo-oligosaccharide | 33 days old/21-d trial | 4 g/kg | Increased villus height, reduced diarrhea | Improved ADG, increased the concentrations of isobutyric and butyric acid and total VFAs in the caecum, and acetic acid, isovaleric acid, and total VFAs in feces | [63] | |
| Resistant starch | 17 days old/21-d trial | 70 and 140 g/kg | Enhanced microbial diversity in colon and reduced diarrhea with 7% resistant starch inclusion in the diet | No effect on growth performance | [64] | |
| Inulin | 42 day old/35-d trial | 40 mg/kg | Increased Lactobacilli and Bifidobacteria and reduced Enterobacteriaceae and Clostridium spp. in the lumen and mucosa of gut | Higher blood hemoglobin | [65] | |
| Lactulose | 25 days old/18-d trail | 10 g/kg | Increased Lactobacilli and the percentage of butyric acid in the colon; an increase in the ileum villous height | Improved the ADG; reduction of the pig major acute-phase protein in serum | [66] | |
| Levan-type fructan | 28 days old/42-d trial | 0, 0.1, 0.5, and 1.0 g/kg | Linear increase in fecal lactic acid bacteria counts with the increase in the dose of levan | Increased ADG and ADFI linearly during days 0–21 and overall; linear increase in the digestibility of DM, CP, and GE | [67] | |
| Galacto oligosaccharide (GOS) | 28 days old/28-d trial | 0, 500, 1000, 1500, and 2000 mg/kg | Increased the number of Lactobacillus and Bifidobacterium, and decreased the number of E. coli in a linear or quadratic dose-dependent manner; decreased serum concentration of pro-inflammatory cytokines but increased anti-inflammatory cytokines in a linear or quadratic dose-dependent manner | Promoted the growth and activities of antioxidant enzyme in a linear or quadratic dose-dependent manner | [68] | |
| Probiotics | ||||||
| Saccharomyces cerevisiae | 27 days old/35-d trial | 1.25 g/kg | Villus length and crypt depth not affected by probiotic but were greater at 5 weeks vs. 2 weeks after weaning; CD4 and CD8 cells were lower at 5 week after weaning | Improved ADG and G:F | [69] | |
| Lactobacillus sobrius | 21 days old (challenged with 1.5 mL suspension of 1010 CFU ETEC F4) | 1010 CFU probiotic in 1 mL skimmed milk/day | Reduced ETEC levels in the ileum | Improved daily weight gain | [70] | |
| Saccharomyces cerevisiae | 21 days old/21-d trial | 5, 10, 20 g/kg probiotic | Increase in jejunal villus height and villus height: crypt depth ratio was also increased; gut IFN-gamma concentration increased on day 21 but plasma IFN-gamma reduced on day 7 and CD4 reduced on day 14 | Feed intake was enhanced with the inclusion of 5 or 10 g/kg; enhanced digestibility of DM, CP, GE with 5 g/kg yeast supplement | [71] | |
| Lactobacillus johnsonii and Lactobacillus mucosae single or combined | 21 days old/21-d trial | 5 × 107 or 108 CFU/g/piglet/day of each strain | Increase in fecal Lactobacillus and reduction in E. coli counts | Both single or combined supplementation increased overall FI and BWG | [72] | |
| Enterococcus faecalis | 24–26 days old/28-d trial | 0.5 × 109, 1 × 109, or 2.5 × 109 CFU/kg of feed | Lower incidence of diarrhea and increase in fecal Lactobacillus counts | Higher ADG and feed efficiency in pigs receiving the highest probiotic dose. | [73] | |
| Bacillus subtilis GCB-13-001 (1 × 109 CFU/kg) | 28 days old/42-d trial | 1 g/kg | Fecal Lactobacillus counts were improved, and E. coli counts were reduced | The BW and ADG improved during all phases, F:G improved during the overall experiment period | [74] | |
| B. coagulans, B. licheniformis, B. subtilis, and C. butyricum mixed dried spores(1 × 1012, 5 × 1011, 1 × 1012 and 1 × 1011 CFU/kg respectively). | 28 days old/42-d trial | 0, 1, 2, and 3 g/kg | Linear increase in fecal Lactobacillus counts and decreased Escherichia coli counts and ammonia (NH3) emission | Linearly increased ADG and ADFI during d 0–7, increased ADG and G:F during d 8–21 | [75] | |
| Bacillus subtilis or Bacillus pumilus 1 × 109 CFU/kg | 21 days old (challenged with ETEC/28-d trail) | 500 mg/kg | Bacillus subtilis supplement alleviated diarrhea severity, enhanced gut health, and reduced systemic inflammation of weaned pigs infected with ETEC F18 | Bacillus subtilis supplementation improved growth performance | [76] | |
| Phytogenics | ||||||
| Mixture of herb extract | Buckwheat, thyme, curcuma, black pepper, and ginger | 21 days old/42-d trial | 250 mg/kg | Reduced fecal E. coli counts | Improved energy digestibility but no effect on growth performance | [77] |
| Plant extract(PE) | Green tea leaves (Camellia sinensis) and pomegranate fruit (Punica granatum) | 24 days old/35-d trial | 8 μL/kg per day PE in drinking water | Reduced fecal E. coli counts in challenged pigs on days 14 and 35 and reduced Enterobacteriaceae on day 35 | Increased ADG from days 28–35 and increase G:F ratio from days 7 to 14 | [78] |
| Brown algae (ethanol extract from Ecklonia sp.) | Eckol | 28 days old/42-d trial | 0.5 and 1 g/kg | Improved intestinal barrier function | Improved growth performance, and reduced the levels of stress hormones (cortisol, epinephrine, and norepinephrine) and antioxidants (superoxide dismutase and glutathione peroxide) | [79] |
Abbreviations: ADG, average daily gain; ADFI, average daily feed intake; ADF, acid detergent fiber; CP, crude protein; DM, dry matter; ETEC, enterotoxigenic Escherichia coli; FCR, feed conversion rate; G:F, gain-to-feed ratio; GE, gross energy; N, nitrogen; NDF, nitrogen detergent fiber; VFA, volatile fatty acid; UMP, uridine 5′monophosphate, GMP, guanosine 5′monophosphate; AMP, adenine 5′monophosphate; CMP, cytidine 5′monophosphate; IMP, inosine 5′monophosphate; UR, Uridine.