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The immune status of replacement gilts, together with that of the sow herd define a major part of herd health stability. To vaccinate, immunize and cool down any possible infectious disease in gilts are key issues to minimize later risks. However, while rearing phases and quarantines include intensive vaccination programs and exposure to pathogens, do current diets provide adequate status to face these challenges? Here are reviewed some nutritional components previously studied to enhance immune status.
Under an immune challenge, oxidative phosphorylation is downregulated in favor of glycolysis, which reduces metabolism efficiency. Immune proteins (i.e. cytokines and acute-phase proteins) are synthetized and released to the bloodstream. Such overabundance of inflammatory cytokines together with oxidative stress cause tissue damage. Inflammation and following antibody production increase energy and amino acids demand, while lethargy and anorexia will highly contribute to protein catabolism. The acute response (i.e. TNFα, IL1β) also antagonizes growth factors which directly suppress growth (Broussard et al., 2001, 2004). Within all this physiological changes, the greatest consequence affecting animal performance is a reduced feed intake. Further problems such coinfections or lameness may also be associated with a lack of adequate immune response. It is not a novel suggestion that nutritionally anticipating to inflammation, and (or) metabolic changes may be a successful strategy to mitigate the negative impact of disease on pig performance.
Over the last 10-15 years, nutritional strategies caught research attention to mitigate or prevent disease (i.e. as alternatives to antimicrobials). Usually, the aim is to reduce pathogen load, or enhance immunity, gut health, digestive function, and set beneficial microbes to ultimately increase performance; yet variety of responses and effectiveness is reported (Adewole et al., 2016; Celi et al., 2017; Pluske et al., 2018). Such research has mostly focused on nursery piglets and less on older pigs i.e. gilt acclimation, multiple-vaccinating, or disease outbreaks.
Taking porcine reproductive and respiratory syndrome (PRRS) as an example, quite some work is focused on soybean. For example, isoflavones genistein and daidzein are soybean components attributed both, positive and negative immune-modulating effects. Feeding genistein concentrations of 200 to 400 ppm to young pigs resulted an active immune modulator. It enhanced virus elimination and increased growth on PRRS challenged pigs (Greiner et al., 2001a). However, the same doses of daidzein only enhanced growth weakly (Greiner et al., 2001b). Increasing dietary soybean meal (SBM) concentration from 21% to 32% in finisher pigs (Johnston et al., 2010) and from 12.5% to 22.5% in nursery pigs (Rocha et al. 2013), improved growth in PRRSv infected pigs. Similarly, Rochell et al. (2015), found that a 17 to 29% increase enhanced growth, immune response, and reduced viral load of pigs under PRRS. More recently, none of these effects were observed when increasing SBM from 10 to 30% in grower pigs (Schweer et al., 2018). Such controversy arise possible interactions with pathogenic variation, genetic differences, age of pigs, and variability of active components content on soybean meal. Variating results indicate that we have much to learn.
Plant extracts, are secondary plant metabolites with some degree of antimicrobial, anti-inflammatory, and anti-viral properties. Those have potential for improving gut mucosal immunity and gut barrier function (Manzanilla et al., 2004; Liu et al., 2013). Some examples are capsicum oleoresin, garlic botanical, and turmeric oleoresin. In a PRRSv infection, plant extracts were shown to delay fever and some cytokine changes over time post-infection, improve immune responses, and growth efficiency (only turmeric oleoresin extract) but without affecting growth (Liu et al., 2013). Current data suggests difficulties to influence performance even when nutritional strategies are capable of modulating immunity.
Vitamin E, has been notably studied for preventing lipid peroxidation under oxidative stress. Antioxidant capacity is highly important in immune cell function where polyunsaturated fatty acids are threatened for oxidative damage. Viral titers of influenza, virus load in lung, as well as IL1β and TNFα were reduced in mice supplemented with vitamin E (Han and Meydani, 2000). Nonetheless, vitamin E did not reduce morbidity nor enhanced growth during acute infection of PRRSv (Toepfer-Berg et al., 2004). Vitamin A, with recognized role for mucosa immune capacity among other roles for innate and adaptive immunity may also provide advantages. Retinoic acid, metabolite from vitamin A is known anti-inflammatory via inhibiting cyclooxygenase 2 (Villamor and Fawzi, 2005); but its potential in pig diseases has not been proved.
Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) from omega-3 are acknowledged fatty acids reported to improve immune cells functionality and reduce cellular inflammation. However, may also reduce T cell signaling and antigen presentation (Shaikh and Edidin, 2007). A 5% substitution of corn oil for fish oil (rich in omega-3) in weanling piglets, showed a tendency to compensate gain after a lipopolysaccharide (LPS) challenge in pigs (Gaines et al., 2003). In another study, 7% substitution was shown to reduce cellular inflammation and improve performance under LPS challenge (Liu et al., 2003). Similarly, high levels of omega-3 (10% fish oil) improved ADFI and ADG in a Staphylococcus aureus model (Langerhuus et al., 2012).
Amino acids are important for immune system. Threonine (Thr) is a major component in g-globulin; and similarly, tryptophan (Trp) demand increases during inflammation (Cuaron et al., 1984; Le Floc’h et al., 2009). In combination Thr and Trp were used in a PRRSv live vaccine challenge (Xu et al., 2015), which increasing ratios to 0.26 Trp:Lys and 0.80 Thr:Lys reduced lung damage and tended to have higher growth performance. In their study, authors observed increased gene expression of Toll-like receptor 3 and 7, which are potent inducers of innate immunity against viral infections.
From this short review, chances for nutritionally intervention on immune status of pigs exist. Nonetheless, earlier elimination of pathogen, reduce pathogen load, and minimize symptoms such reduce performance loss, seems to have a poor response in most published data. The interactions among concomitant pathogens and factors such animal genetics and age are highly important. The role of nutrition in gilt immunity during quarantine has not been studied and possible effects to reproductive performance or longevity are unknown. This debate is not sufficiently addressed in the swine industry and improving immune status during multiple vaccination and quarantine challenges is still an opportunity to be elucidated.
