It is well accepted that healthy business starts with healthy animals, and it is well known that a healthy animal starts with a healthy gut.

What do we mean by 'gut health'?

The term gut health in animals is not well-defined, however, several indicators, such as those related to gut structure and function, and microbial population, incidences of diarrhea have been used to describe gut health outcomes (Balachandar and Nyachoti, 2017). Kogut and Arsenault (2016) describe gut health as the “absence/prevention/avoidance of disease so that the animal is able to perform its physiological functions in order to withstand exogenous and endogenous stressors”. The factors that affect gut health and growth performance in piglet husbandry practices include feeding strategies, exposure to overcrowding stress, sanitary, and disease conditions (Balachandar and Nyachoti, 2017). So, keeping the gut healthy particularly in piglets is not an easy task. Although several factors could potentially affect performance in the neonatal gut of the piglet, weaning is the most important and where one should pay special attention.

Factors causing weaning stress

Factors causing weaning stress are:

1. transition in diet,
2. exposure to dietary antigens,
3. exposure to pathogens,
4. social stress including separation from the mother, and
5. environmental change.

From these factors, nutrition management can help to reduce the causes of the weaning stress on the first three factors.

Intestinal health

Regarding intestinal health, many authors have reported that there is a reduction in villi height (villi atrophy) and an increase in crypt depth (crypt hyperplasia) after weaning which compromises the digestion and absorption of the feed and contribute to post-weaning diarrhea. Weaning may cause a significant reduction of approximately 50%, in the height of the villi and this effect can be maintained, even after 14 days post-weaning. However, good feed intake can promote an improvement in villus height in the first week after weaning (Marion, J. et al. 2002; Pluske, J.R. et al., 1997). Weaned piglets are suddenly forced to undergo a transition from milk to solid diets including complex protein (Ma et al., 2019a, b), which can result in diarrhea or even death. At weaning, adaptation of pancreatic and brush border enzyme activities occurs during the first two weeks with an initial reduction in activity (Hampson and Kidder, 1986; Jensen et al., 1997; Levesque et al., 2012). This lag in digestive enzyme activity adaptation is related to the post-weaning growth delay, with the greatest reduction in growth coinciding with the lowest enzyme activities (Hampson and Kidder, 1986). As a result of this low enzyme activity, some nutrients may escape from absorption in the small intestine will flow into the large intestine and valuable nutrients become available for pathogenic bacteria. It is for this reason that pre-starter diets must be prepared with highly digestible and easy absorbable ingredients, to minimize the escape of nutrients to the large intestine (Ma et al., 2019a). When introducing vegetable ingredients, one suggestion to improve diet management would be to define the point at which the pancreatic enzyme secretion of the piglet might be enough for hydrolysis of a diet replacing milk (Corring et al., 1978).

Soybean meal

Soybean meal (SBM) is the most commonly used vegetal protein source in monogastric diets (Feng, J. et al., 2007a; Stein, H.H., et al., 2008). SBM is a less expensive protein source with lower digestibility than animal-derived ingredients (Cervantes-Pahm and Stein, 2010), and contains antinutritional factors (ANFs) which are critical to piglet health including antigens like glycinin and β-conglycinin, trypsin inhibitors, and α-galactosides such as raffinose and stachyose (Li, D.F. et al., 1990; Friesen et al., 1993; Mawson et al., 1994; Zhang et al., 2001; Choct et al., 2010; Koo, B., et al., 2017; Zheng, L., et al., 2017; Ma et al., 2019a; Ma et al., 2019b).

Antigens have a negative impact on the gut membrane, causing inflammatory lesions and compromising the gut’s ability to absorb nutrients. Glycinin and β-conglycinin are potential antigenic and allergenic compounds, causing hypersensitivity in pigs (Li et al., 1990; Holzhauser et al., 2009). Negative effects include increased mucus production, intestinal villi atrophy and cellular apoptosis. Another consequence of a compromised, more permeable gut is that large and potentially harmful molecules can pass the gut lining and cause an allergic reaction. The subsequent activation of the immune system draws on energy and nutrients, reducing the resources available to support piglet growth.

Trypsin inhibitors (TI) are well known to reduce protein digestibility (Yen, J.T. et al., 1977) which then passes unabsorbed into the colon without contributing to animal growth. In the colon, undigested protein is fermented by bacteria, including potential pathogens, which produce toxic end-products that impair the integrity and functions of the intestinal membrane. Toxins absorbed from the gut activate the immune system, which requires energy to combat the toxins. In this way, there is less energy available for piglet growth, resulting in lower performance.

Oligosaccharides such as Stachyose and Raffinose in soy protein are fermented by bacteria in the small intestine as the necessary enzymes are not available to break them down. Gas produced by the fermentation process causes flatulence and therefore discomfort to the animals. On the other hand, oligosaccharides that are not fermented have an osmotic effect that draws water from the gut lining, speeding up gut transit time and leading to scouring (Smiricky, M.R., et al, 2002; Beloshapka, A.N. et al., 2016; Navarro, D., 2021; Zhang, Q. et al., 2021).

To avoid providing these ANFs, diets for weanling pigs often contain animal protein sources, which are more expensive than SBM and in some cases as is the case with some fish meals, with high nutrient variability. If some vegetable protein like SBM is to be considered in this type of feeds, some form of processing (heating/enzymolitic treatment) in this ingredient should be considered to reduce the content of the ANFs, and improve nutritional value (Wiseman, J., 1982; Li, H. et al., 2021; Zheng et al., 2017).

SBM can be processed to extruded full-fat soybean (EFS), soy protein concentrate (SPC), fermented SBM (FSBM), or enzyme-treated SBM (ESBM), which all have reduced concentrations (in different degrees) of antinutritional factors compared with SBM, and processed soybean products are, therefore, more tolerable to young pigs than conventional SBM (Li, H. et al., 1990, Navarro, D. et al., 2017). EFS is the soybean treated with extrusion and a common soybean protein source. SPC is the processed soybean product as a result of the removal of most water-soluble and non-protein constituents. FSBM is a product manufactured by Microbial fermentation in an incubator (Feng et al., 2007b; Labadan, D.M.D., 2014; Zarkadas L.N. and J. Wiseman. 2005; Zhang et al., 2013). ESBM is an enzyme-treated SBM with minimal concentrations of ANFs. It has been found that the concentration of small peptides are increased after the enzyme treatment ( Ma, X.K. et al., 2019b), which is beneficial to weaned pigs with potentially limited gastric HCl secretion needed for protein digestion.

Ma, X.K. et al. (2019b) demonstrated that concentrations of glycinin, β-conglycinin and TI were reduced in ESBM, confirming that enzyme treatment is an effective method for eliminating these antinutritional factors in SBM. ESBM could be used to substitute animal feed proteins to improve performance in weaned pigs based on the beneficial effects on antioxidant capacity, immunity and intestinal barrier function. Therefore, ESBM has great potential to improve the gut health of young piglets (Ma, X. et al., 2018; Zhou, S.F. et al., 2011).

Nursery diets

If SBM is considered to be included in weaning diets, an SBM product with reduced ANFs should be consider to manipulate diets to a safe ANFs content in the final feed.

In this regard, Ma, X.K. et al., (2019b) concluded that ESBM improved Average Daily Gain and Gain:Feed, and reduced diarrhea rate in weaned pigs when compared to SBM, SPC, FSBM, and Fish Meal (Table 1) which was linked to their positive results in improvements on antioxidant capacity, immunity and intestinal barrier function. These results are in line with previous studies showing that the performance of weaned pigs was enhanced by ESBM when compared to SBM (Yang et al., 2007; Jones et al., 2017).

Some work has demonstrated that ESBM could be an effective plant protein resource when comparing to EFS to alleviate weaning stress in pigs (Li et al., 2021; Long, S. et al., 2021). In this regard, Li et al. (2021) investigated the impact of ESBM replacing EFS protein on the performance, dietary nitrogen digestibility, cecal fermentation characteristics, and bacterial community in newly weaned piglets. In this study, piglets in the ESBM group showed greater feed efficiency, and lower diarrhea rate (Table 2) and better nitrogen digestibility (Table 3) in comparison to piglets in the EFS group (P < 0.05). Additionally, this group found that a relative abundance of beneficial bacteria was increased, and some pathogenic bacteria was reduced in the cecum of piglets fed with ESBM diet, which may contribute to the improvement of intestinal health and attenuation of weaning stress of piglets.

According to the presented information, it is recommended to swine nutritionists to include in their diets the best possible quality feed ingredients such as ESBM which has the lowest ANFs. The latter will help to promote a healthy gut to piglets on the starting phases of their lives which in turn leads to healthy animals and finally to a healthy business. It can also be of a good help to count with trustworthy raw material providers which must supply consistency on feed ingredient composition to the Nutritionist managing the diets in order to avoid over/under formulation, and as a consequence keeping high and constant quality on the finished feeds.