How can nutrition help pigs facing health challenges?

Pigs in commercial production systems are frequently challenged by a wide range of factors. Among them, health challenges (including poor hygiene of housing conditions) result in immune system activation which, in turn, may negatively impact the health status and growth performance of animals (Le Floc’h et al., 2014). In order to minimize the negative effects of inflammatory challenges, especially in view of the ban of in-feed antibiotics in livestock production, nutritional strategies including feed additives have been widely studied (Zheng et al., 2021).

Nutrients can modulate the immune response, the development of the gut, and the antioxidant capacity of pigs. Therefore, a better understanding of their modulatory effects may support nutritionists in formulating more adapted diets and contribute to the development of nutritional strategies to improve animal performance, well-being, and health (Rodrigues et al., 2022).

Besides being building blocks of proteins, amino acids (AA) are known to be nutrients that contribute to health maintenance. Changes in AA plasma concentrations have been observed in inflammatory-challenged pigs (Fraga et al., 2021), which may be mainly associated with a greater demand to support the immune system functions (synthesis of acute phase proteins, immune cell proliferation, and other compounds related to body defenses; Le Floc’h et al., 2018).

Functional amino acids

Functional AA were defined as those AA that exert functions other than being precursors of proteins (Wu, 2013; Figure 1). For instance:

• Experimental data have demonstrated the immunometabolic function of methionine (Met, the second limiting AA for pigs) whose metabolism can generate intracellular antioxidants, such as glutathione and taurine (Sun et al., 2016).
• There is evidence that stimulation of the immune system affects the metabolism of tryptophan (Trp) and arginine (Arg), which in turn are related to essential immune response functions (Le Floc’h et al., 2010; Campos et al., 2019).
• Approximately 10 to 13% of the glycoproteins present in intestinal mucus are constituted by threonine (Thr; Pluske et al., 2018).
• Branched-chain amino acids (BCAA; including valine, leucine, and isoleucine, Val, Leu and Iso; respectively) are also involved in important pathways controlling immune responses (synthesis of defense cells [lymphocytes, neutrophils, and macrophages] and immunoglobulins; Ren et al., 2015).

For growing pigs housed in poor hygiene conditions and inoculated with Salmonella Typhimurium, dietary supplementation with a blend of AA (Met, Tre, and Trp 20% above NRC recommendations, 2012) was associated with reduced inflammation, increased body weight gain, and protein deposition compared to a control diet (Valini et al., 2023). Accordingly, a supplemented diet with a blend of AA (Trp, BCAA, Arg, and cystine) supported pigs weaning transition and alleviated post-weaning diarrhea (Wessels et al., 2021).

Polyphenols

Besides AA, plant extracts containing proanthocyanidins, the most common and consumed dietary polyphenols, are also characterized by diverse bioproperties, such as antioxidant activity and ability to modulate the intestinal microbiota (Andersen-Civil et al., 2021).

In a meta-analysis considering 23 studies published from 2010 to 2023, Fraga et al. (2023a) found that pigs fed with dietary polyphenols supplementation had greater feed efficiency and reduced inflammation (evidenced by lower plasma concentrations of malondialdehyde; MDA) than non-supplemented pigs.

Regarding the association between AA and polyphenols, in a recent study conducted at INRAE (Saint Gilles; France), pigs fed with a mix of functional AA and grape extract polyphenols during 6 weeks of the post-weaning period were able to maintain their performance in the subsequent phase (growing phase), when they were challenged by poor conditions and fed a common diet (Table 1; Fraga et al., 2023b). These results demonstrated that these supplemented pigs had a better capacity to cope with a subsequent inflammatory challenge applied in the beginning of growing.

Table 1. Growth performance of pigs housed in good and poor hygiene conditions previously fed with a control diet supplemented or not with a mix of functional AA and grape polyphenols (AAP and Control diets, respectively).¹

¹ Adapted from Fraga et al., 2023b.
² Pigs were fed the CNT or AAP diet for 6 weeks after (from Week 0 to 6). The AAP diet consisted of a control standard diet (CNT) supplemented with 0.2% of a mix of functional amino acids (L-arginine, L-cystine, L-leucine, L-valine, L-isoleucine, and L-glutamine) and grape polyphenols.
³ Pigs were housed in good (good) and poor (poor) hygiene housing conditions for 3 weeks (from week 7 to 9) and were fed a standard diet.
⁴ Standard error of the mean.
⁵ Probability values regarding the fixed effects of experimental diet (Diet: Control and AAP), hygiene condition (Hyg: Good and Poor), and interaction (Diet x Hyg).
⁶BW: Body weight, ADFI: Average daily feed intake, ADG: Average daily gain.
^{a, b} Within a row values with different superscripts differed (P ≤ 0.05).

General perspective

Pig diets are usually formulated based on nutritional requirements estimated under ideal production conditions (health, environment, temperature, housing conditions, etc). Nutritional programs have limitations in the practical context of production since they do not consider the increased demand for nutrients in situations of immune system activation. Under these conditions, an imbalance between dietary nutrients and nutrients needed for immune and productive functions may occur. Therefore, it is necessary to find alternatives to antibiotics to improve or maintain the health status of animals in order to allow the development of more sustainable production systems.