The Role of Milk Oligosaccharides in Enhancing Intestinal Microbiota, Intestinal Integrity, and Immune Function in Pigs: A Comparative Review

Abstract

The objective of this review was to identify the characteristics and functional roles of milk coproducts from human, bovine, and porcine sources and their impacts on the intestinal microbiota and intestinal immunity of suckling and nursery pigs. Modern pig production weans piglets at 3 to 4 weeks of age, which is earlier than pigs would naturally be weaned outside of artificial rearing. As a result, the immature intestines of suckling and nursery pigs face many challenges associated with intestinal dysbiosis, which can be caused by weaning stress or the colonization of the intestines by enteric pathogens. Milk oligosaccharides are found in sow milk and function as a prebiotic in the intestines of pigs as they cannot be degraded by mammalian enzymes and are thus utilized by intestinal microbial populations. The consumption of milk oligosaccharides during suckling and through the nursery phase can provide benefits to young pigs by encouraging the proliferation of beneficial microbial populations, preventing pathogen adhesion to enterocytes, and through directly modulating immune responses. Therefore, this review aims to summarize the specific functional components of milk oligosaccharides from human, bovine, and porcine sources, and identify potential strategies to utilize milk oligosaccharides to benefit young pigs through the suckling and nursery periods.

Keywords: immunomodulation; intestinal microbiota; milk coproducts; milk oligosaccharides; nursery pigs; suckling pigs.

Figure 2

Composition of the six common milk oligosaccharides grouped into their respective major subclasses of MO found in pooled early milk from human [25,26], bovine [7,29], and porcine sources [8,32,34]. Human milk contains the greatest concentration and diversity of MO of all studied mammals to date [11].

Figure 1

Examples of the structures of six common milk oligosaccharides, grouped into three primary subclasses. Abbreviations: GlcNAc: N-acetylglucosamine; NeuAc: N-acetylneuraminicacid.

Figure 3

Summary of the generalized mode of action for the three major subclasses of MO. 1: Neutral N-containing MO could increase populations of potentially beneficial bacteria, such as Bifidobacterium spp., prevent pathogen binding to the host epithelium by steric hinderance, thereby reducing oxidative stress and improving intestinal morphology. 2: Sialylated MO could increase populations of potentially beneficial bacteria, prevent pathogen binding by competitive binding to pathogens, thereby increasing serum IgG and decreasing serum TNF-α. 3: Fucosylated MO increase the populations of potentially beneficial bacteria and prevent pathogen binding by competitive binding to pathogens, thereby reducing the secretion of inflammatory cytokines and intestinal inflammation [41,42,43,44,45,46,47,48,49,50,51,52,53].