Table 2.

Effects of pre-weaning dietary interventions in milk replacer on the gut development of artificially reared piglets. ↓ Significant decrease at p < 0.05; ↑ Significant increase at p < 0.05; = No significant difference; BW = body weight.

Reference	Dietary Intervention(s)	Intervention Period (Age)	Age at Sampling	Effects on Gut Development versus a Control Milk Replacer
[53]	Polydextrose (2 g/L) + Fructo-oligosaccharides (2 g/L)	1–14	7, 14	Lowers digestive enzyme production at both sampling days: ↓ Lactase, sucrase, disaccharidase and aminopeptidase N activity (ileum) ↓ Dipeptidyl peptidase IV activity (jejunum, ileum) = Small-intestine weight and length = Cytokine expression (ileum) = Faecal consistency
[61]	Polydextrose (2 g/L) + Galacto-oligosaccharides (2 g/L)	2–33	33	= Small-intestine weight and length ↓ Total volatile fatty acids (colon, no differences in caecum and faeces) ↑ Dry matter of colon digesta ↓ Dry matter of faeces
[53]	Galacto-oligosaccharides (2 g/L) + Inulin (2 g/L)	1–21	21	= Small-intestine weight and length = Immune cell population = Nitric oxide synthase activity = Cytokines IL-6 and TNF-α in blood
[54]	Galacto-oligosaccharides: 0.8%	1–26	4, 27	Modulates gut microbial population and improves intestinal morphology and barrier function: ↑ Duodenum villus height, villus area, villus-to-crypt ratio (d4), villus width (d27) ↑ Jejunum villus height (d27) ↓ Caecum pH (d4, no other pH differences) ↑ Caecum butyric acid (d27) ↑ Lactobacillus, bifidobacterium in faeces (d27) ↑ Maltase activity (colon: d4, caecum: d27) ↓ Lactase, sucrase, maltase activity (ileum, d27) ↑ mRNA expression of defensins (colon, d4) ↑ mRNA expression of tight-junction proteins in different segments of the intestine (d4, d27) ↑ Tight-junction protein expression (duodenum, colon, d27) ↑ Secretory IgA from saliva (from d19)
[62]	Galacto-oligosaccharides: 8 mg/mL	3–25	25	↑ Relative large-intestine weight in males, but not females = Small-intestine weight ↓ Haematology and clinical chemistry blood parameters
[63]	Galacto-oligosaccharides (7 g/L) + milk fat globule membrane-10 (5 g/L) + polydextrose (2.4 g/L) + bovine lactoferrin (0.6 g/L)	3–33	33	Modulates gut microbiota population and stimulates gut function: = Intestinal weight and length, small-intestinal morphology ↓ Colon area ↑ Parabacteroides, Clostridium IV, Lutispora (colon) ↓ Mogibacterium, Collinsella, Klebsiella, Escherichia-Shigella, Eubacterium, Roseburia (colon) ↑ Lactase activity (jejunum), lactase-to-sucrase activity (duodenum, ileum; no difference in jejunum) = Sucrose activity (in any part) ↑ Vasoactive intestinal peptide expression (ileum)
[56]	Bovine colostrum	23–31	31	Reduces colonisation by E. coli and modulates intestinal immune system: ↓ Diarrhoea frequency ↓ E. coli in jejunal and ileal tissue and content in non-inoculated intestinal samples, but not in ETEC F18-inoculated samples ↓ TLR-4 and IL-2 gene expression (jejunal and ileal mucosa) = Ig concentrations in mucosa and plasma
[55]	VP: palm + rapeseed oil VM: VP + milk fat globule membranes (MFGM) MM: VM + sunflower + milk fat	2–28	7, 28	VM and MM: ↑ relative jejunum weight and mucosal density at d7 and d28, ↑ ileum mucosal density at d28, = digestive enzyme activity, = epithelial barrier permeability MM: ↓ protein digestion (casein),↑ interferon γ secretion from mesenteric lymph node cells, x= bacterial diversity, ↑ Parabacteroides, Escherichia/Shigella, Klebsiella, ↓ Clostridiales Family XIII, Veillonellaceae
[64]	Fat origin: only plant lipids or a half-half mixture of plant and dairy lipids	2–28	33	= Short-chain fatty acids (faeces)
[65]	Yeast β-glucans: 5, 50 or 250 mg/L	2–21	7, 21	= Small-intestine length and weight = Ileal crypt depth, villus height, ascending colon-cuff depth = T cell phenotypes, cytokine gene expression, cell proliferation
[66]	Wheat: up to 40%	11–25 1	25	↓ Relative full stomach weight ↑ Sucrase, maltase ↑ Leukocytes, neutrophils
[67]	Pectin: 2 g/L or 10 g/L	2–23		10 g/L pectin: ↓ feed efficiency, ↓ apparent ileal and total tract digestibility of dry matter, crude protein and energy 2 g/L pectin: ↓ apparent total tract digestibility of dry matter

¹ A basal milk replacer was given from Day 3 to Day 11 after birth.