1. Introduction
Pre-weaning piglet diarrhea is well recognized as a major concern in the swine industry. The diarrhea causes malabsorption and excessive secretion of water and electrolytes into the intestine resulting in watery feces, nausea, abdominal cramps, shivering, decreased feed intake, growth retardation and increased piglet mortality [
1]. Several pathogens—as causative agents for pre-weaning piglet diarrhea—include
Escherichia coli,
Enterococcus hirae, Clostridium difficile,
Clostridium perfringens,
Salmonella spp.,
Campylobacter spp., rotavirus, coronavirus and
Cryptosporidium spp. [
2]. In addition, the use of antibiotics, various preventive measures and applications of feed additives have been alternatively introduced to improve intestinal health and reduce the incidence of diarrhea in newborn piglets.
Probiotics are defined as live microorganisms, which confer a health benefit on the host, when administered in adequate amounts [
3]. Probiotics have been introduced as alternative feed additives, aiming to reduce antimicrobial resistance and drug residues in the swine production chain [
4].
Clostridium butyricum (
C. butyricum)—a Gram-positive obligate anaerobic bacillus—has been acknowledged for its probiotic capacity; i.e., modulation of gut microbiota, improvement of intestinal barrier functions or protection against pathogenic bacteria, which enhance growth and reduce diarrhea incidence in piglets [
5]. The principal effects of
C. butyricum probiotics are associated with its ability to produce short-chain fatty acids (especially butyric acid), amino acids, enzymes, and vitamins which play a crucial role in energy metabolism and the development of healthy intestinal epithelial cells [
5]. In addition,
C. butyricum feed additives are reported to be associated with enhanced digestibility and nutrient absorption of pigs [
4]. Therefore, many studies focused on the influence of the presence of
C. butyricum probiotics in the feed of a sow herd—especially during late-gestation and lactation period—on the production and quality of colostrum and milk of the sows [
6,
7,
8]. It is well recognized that sow colostrum and milk are essential sources of energy, passive immunity and nutrients that support the growth and survival of newborn piglets during the lactation period [
9]. Various strategic dietary supplements aiming to ameliorate yields, biochemical and immunological composition in sow colostrum and milk have been attempted [
10,
11,
12]. Regarding the effects of dietary probiotics, alterations in gross chemical composition—i.e., fat, protein, lactose, milk-solids-not-fat, IgA and IgG—in sow colostrum and milk have been indicated in many studies [
6,
7,
13,
14]. Nevertheless, changes in minor milk components affected by dietary probiotic intake have not been well investigated.
Metabolomics—a comprehensive characterization of small molecular weight metabolites (<1.5 kDa) present in biological matrices—has recently been acknowledged in lactation biology, milk and dairy research [
15]. This high-throughput approach allows a better understanding of dynamic changes in milk metabolome, influenced by various inherent and environmental factors in dairy production [
15]. Although metabolomics has been applied in swine milk research [
16,
17,
18], publications using this approach to investigate the impact of probiotic feed additives on the alteration in sow milk metabolome are rather limited [
19]. This information could provide a better understanding and novel insights into the relationships between probiotic-induced changes in sow milk composition and piglet performance.
Therefore, the aims of this study were to investigate the impact of dietary C. butyricum probiotic administration during the late-gestation and lactation period on: (i) changes in the performances of lactating sows and pre-weaning piglets; along with (ii) the alterations in fatty acid and non-volatile polar metabolite profiles of sow colostrum and milk.
4. Discussion
The
C. butyricum has benefits for animal health; i.e., improving gut microbiota and intestinal barrier functions leading to increase the growth performances of both sows and piglets [
4,
5]. Relative backfat loss serves as an important parameter that indicates sow energy mobilization. It should be noted that backfat thickness is associated with a variety of reproductive parameters. For example, loss of backfat thickness could increase the number of stillborn piglets and decrease litter size [
27]. Moreover, excessive backfat loss during lactation is associated with prolonged weaning-to-estrus intervals and reduced farrowing rates [
28,
29]. It is recognized that 15–20% of primiparous sows are often culled due to reproductive problems [
30,
31,
32]. The present study found that the application of dietary
C. butyricum probiotic additive during late gestation throughout the entire lactating period of the sows could reduce relative backfat loss, especially in primiparous sows. It has been documented that probiotics enhance intestinal barrier function and enzymatic production, which leads to improved nutrient digestion, health, and reproductive performances of the sows [
4,
33,
34].
C. butyricum probiotics are noted to have a capacity to produce short-chain fatty acids (SCFAs) such as butyrate from carbohydrate metabolism, that could provide energy for epithelial cells and promote intestinal barrier function [
35,
36]. Furthermore, Niu et al. [
37] demonstrated the association between a high abundance of
Clostridium spp. in the gastrointestinal tract and higher backfat thickness. Therefore, feeding sows with
C. butyricum probiotic additives may affect energy metabolization and digestion. Indeed, our result was consistent with the work of Konieczka et al. [
38], who also found that feed formulation with probiotic
Bacillus subtilis and
Bacillus amyloliquefaciens could reduce backfat thickness loss in sows during lactation.
In the present study, the average body weight of all piglets at birth and during lactation was not affected by the
C. butyricum probiotic additive to the sow’s diet during late gestation to lactation. Nevertheless, the piglets of sows fed with
C. butyricum incorporated in their diets had higher body weights on days 21 than those of the control group.
C. butyricum probiotics have been found to enhance the growth performance of suckling piglets by improving milk quality and increasing the lactose and protein content in milk [
39]. In contrast, in our study, the
C. butyricum probiotic additive only tended to improve the lactose content in mature milk (day 17;
p = 0.074), which is a source of energy for piglet metabolism.
Direct feeding of
C. butyricum probiotics has been shown to promote the growth performance of piglets by improving enterocyte morphology, increasing villus height, improving the villus height–cell depth ratio and strength of the intestinal mucosa cell wall, enabling better nutrient absorption and a reduced diarrhea score [
40,
41]. Moreover, López et al. (2021) found that
C. butyricum increased intestinal butyric acid levels, thereby improving the intestinal wellness and health status [
42]. In agreement with the present study, enhanced growth coinciding with the reduction of diarrhea scores in pre-weaning piglets was also observed. However, it could be an indirect effect of lactating sows fed with probiotic
C. butyricum incorporated diets. The results showed that piglets born from
C. butyricum-fed sows had high body weights at day 21 when compared to the control group. Moreover, feeding
C. butyricum probiotics to sows reduced the incidence of diarrhea in piglets throughout the lactation period. Pre-weaning piglet mortality is primarily caused by crushing, low viability and diarrhea [
43,
44]. Therefore, preventing diarrhea in suckling piglets is essential to minimize these problems. Probiotic additives have been shown to reduce piglet diarrhea both before weaning [
45,
46] and after weaning [
41,
42]. In general, the
C. butyricum—a butyric acid-producing bacterium—lowers gut pH, which enhances antibacterial effects [
47,
48]. Cao et al. [
39] indicated that
C. butyricum probiotic additive promotes an intestinal microecology that supports beneficial bacteria subpopulations, such as
Bacteroidetes and
Prevotellaceae spp., while reducing harmful bacteria, including
Streptococcus,
Escherichia, and
Shigella, in pre-weaning piglets. Tang et al. [
5] further indicated that supplementing with this probiotic strain significantly reduces the colonization of harmful bacteria in the intestinal tract and enhances the expression of tight junctions (TJs) to improve intestinal barrier function. Furthermore, a reduction in serum lipopolysaccharides endotoxin concentrations, the major factors that induce inflammation and disrupt TJ protein, was found in sows fed with
C. butyricum probiotics on day 21 of lactation [
39]. This is in agreement with Kong et al. [
49] who reported that consumption of
C. butyricum probiotics benefited the gastrointestinal tract microbiome by increasing the beneficial bacteria and reducing harmful pathogens in the intestines of children [
50]. Although
C. butyricum probiotic additive in the present study was applied in the diets of sows, significant improvement in diarrhea incidence was remarkable in piglets. This might be due to the bacteria from the sows which colonized the mammary teats and were transferred to the piglets during suckling a few days after birth [
34,
41]. Therefore, the addition of
C. butyricum probiotics additive to the diet of sows may increase the concentration of butyric acid in the gastrointestinal tract of the piglets. As a result, piglets from sows receiving probiotics have a lower incidence of diarrhea and gain a higher body weight. This improvement in digestive function and absorptive capacity of the intestine contributes to the overall health and growth of the piglets.
The significant effect of dietary
C. butyricum probiotic additive was neither observed on gross chemical composition nor immunological quality of colostrum and milk of the sows in the probiotic-treated group in this study. This was in accordance with two studies which previously reported no significant influence of probiotic administration—i.e.,
C. butyricum [
34] and
Bacillus licheniformis and
Bacillus subtilis [
51]—on the contents of fat, protein, and lactose in sow colostrum. However, both studies found significant changes in fat, protein and lactose content in the mature milk of sows fed with probiotics. Indeed, many studies have reported significant impacts of probiotic administration—i.e.,
Bacillus subtilis and
Bacillus licheniformis [
8,
13],
Saccharomyces boulardii [
7],
Saccharomyces cerevisiae [
14]—on the variations in fat, protein, lactose and dry matter content in both colostrum and mature milk of sows. Regarding immunological parameters, significant rises in IgG, IgA and IgM level in sow colostrum were found after probiotic administration in many studies [
8,
14,
45]. In the present study, the effect of dietary
C. butyricum probiotic additive on the colostral immunoglobulin contents could not be observed. It should be mentioned that inconsistent and very divergent results have been documented regarding the scientific benefits of probiotics when applied in the field. This can be related to the variations of probiotic strains, dosage and delivery methods; sow individuality and herd; animal housing and farming practices, as well as other environmental factors linked to specific swine production systems [
4]. In addition to there being no significant effect on gross chemical and immune components, fatty acid and non-volatile polar metabolite profiling was performed to provide more insights on the impact of dietary
C. butyricum probiotic additive on the metabolome of sow colostrum, transient and mature milk in this study.
It is well recognized that nutritional strategies during late gestation and the lactation period can induce changes in FA composition in sow colostrum and milk [
52]. Alterations in milk FA profiles linked to probiotic administration have been reported in goats [
53], ewes [
54] and dairy cows [
55]. However, information regarding the effect of probiotic administration on FA modification in sow milk is rather limited. Our results demonstrated a substantial impact of dietary
C. butyricum probiotic additive on sow milk FA profiles. A continued distinction pattern of FA profiles between the control and
C. butyricum treatment groups was observed in the colostrum, transient and mature milk of the sows. PLS-DA derived VIP scores suggested that variations in the concentration of: (i) saturated fatty acids (SFA) including caprylic (C8:0), capric (C10:0), lauric (C12:0), arachidic (C20:0) and behenic (C22:0) acid; (ii) monounsaturated fatty acids (MUFA) including myristoleic (C14:1), palmitoleic (C16:1) and paullinic (C20:1n7) acid; and (iii) polyunsaturated fatty acids (PUFA) including linolenic (C18:3n3), eicosadienoic (C20:2n6), eicosatrienoic (C20:3n3), docosatetraenoic (C22:4), DPA (22:5n3) and docosahexaenoic (C22:6n3) acid were accountable for the discrimination. Although chemometric analysis revealed a good distinction pattern in colostrum and milk FA profiles associated with probiotic
C. butyricum consumption, the
p values of individual FAs were not statistically significant (
p > 0.05). The most prominent increase in palmitoleic acid (C16:1) was detected in colostrum (
p = 0.059) and transient milk (
p = 0.006) of the sows in the treatment group. Also, the concentrations of lauric (C12:0), myristoleic (C14:1) and linolenic (C18:3n3) acid tended to increase in the transient and mature milk of the sows in the
C. butyricum treatment group. The higher levels in the milk FA could be attributed to improved nutrient digestion and absorption of the sows induced by the
C. butyricum probiotics. Increasing trends of FAs in sow milk were also observed after probiotic yeast intake in the study of Domingos et al. [
56]. It has been documented that certain medium- and long-chain FAs have promising antibacterial activities along with bioactivities to enhance epithelial barrier functions and gut health [
57,
58]. Therefore, a higher abundance of these FAs in milk might be linked to the reduction of diarrhea scores in pre-weaned piglets belonging to the sows in the probiotics treatment group of this study.
The application of non-targeted
1H-NMR metabolomics is well acknowledged in lactation research. The advantage is to provide comprehensive characterization of overall metabolites present in milk and their modifications under different conditions [
59]. Information regarding changes in milk metabolite profiles after probiotic administration has been reported in livestock such as dairy cows [
60], donkeys [
61] and sows [
6,
7,
8,
19,
45,
56]. Additionally, parity numbers and lactation stages were found to be the main factors influencing the composition of metabolomics in colostrum and milk in both monogastric and non-monogastric animals [
18,
62]. Our results demonstrated a substantial impact of dietary
C. butyricum probiotic additive on the metabolite profiles of sow milk. A good distinction between the control and
C. butyricum treatment groups was notably observed in colostrum and mature milk. PLS-DA-derived VIP scores suggested that variations in the concentration of certain carbohydrates, amino acids, amines, organic acids as well as their derivatives were accountable for the discrimination. It should be noted that the concentration of most indicative metabolites significantly decreased (
p < 0.05)—i.e., ribose, dimethylamine,
N-acetylglutamate, O-acetylcholine, sn-glycero-3-phosphocoline, UDP-galactose, UDP-glucose, UDP-
N-acetylglucosamine and uracil—or tended to change (
p < 0.10)—i.e., lactose, lactate, carnitine, choline,
N-acetylglucosamine,
O-phosphocholine and threonine—in the milk of sows in the probiotics treatment group. The influence of the dietary probiotic
Bacillus subtilis and
Bacillus amyloliquefaciens applications on sow milk metabolome has been reported by Saladrigas-García et al. [
19]. In their study, variations in milk metabolites—especially lactose, UDP-
N-acetylglucosamine, creatine phosphate, UDP-galactose and glycoprotein—were found to be associated with administration of the tested probiotic
Bacillus strains. In this study, similar indicative metabolites—i.e., lactose, UDP-N-acetylglucosamine, and UDP-galactose—were observed in association with the use of the probiotic,
C. butyricum. Another recent study focusing on the impact of multispecies probiotics (SLAB51)—consisting of
Streptococcus thermophilus,
Bifidobacterium lactis,
Lactobacillus brevis,
Lactobacillus plantarum,
Lactobacillus paracasei,
Lactobacillus acidophilus, and
Lactobacillus helveticus—administration on donkey milk metabolome found significant changes in the concentration of 12 metabolites—i.e., lactose,
O-phosphocholine, sn-glycero-3-phosphocholine, 4-pyridoxate, caprylate, isovalerate, butyrate, 2-oxoisocaproate, glucose, glucose-1-phosphate, glutamine, and 4-hydroxyphenilacetate—in donkey milk (
p < 0.05) induced by administration of the probiotic mixture SLAB51 [
60]. Moreover, this study found a decreasing trend in the concentration of lactate (
p = 0.16) and threonine (
p = 0.14) in donkey milk induced by SLAB51 probiotics. Alterations in lactose, lactate, threonine,
O-phosphocholine and sn-Glycero-3-phosphocholine contents were also linked to the application of the
C. butyricum probiotics in our work. Nevertheless, it should be mentioned that the beneficial effects of dietary probiotic administration on milk production and compositional changes reported in various livestock species are very case-specific and still inconclusive. Inconsistent findings and great variability in results could be due to probiotic-specific factors—e.g., probiotic strains and mixed formulation, dosage, mode and duration of administration to the subject animals—as well as host-specific factors; e.g., animal species and breed, health and physiological status, digestive system and gut health, diet composition and feeding regime [
60]. Modifications in milk composition could be mediated by changes in digestive efficiency, nutrient absorption and metabolic response of the sows induced by probiotics and other beneficial microbes in their gut microbiota [
19]. Therefore, further research is needed to better understand the mechanisms by which probiotic administration can impact milk composition, and to determine the optimal dosages and feeding durations for various probiotic strains. Moreover, the impact of probiotics on the fecal microbiota of sows and piglets is another point of interest that requires further investigation.