Immune competency is essential for the proper response of the organism to different stressors (e.g., bacteria, fungi, and viruses) that compromise the body’s balance and the animal’s health. Such competence is acquired early in the first stages of life, basically through the ingestion of immunoglobulins in colostrum and adequate nutrients present in breast milk (Rooke & Bland, 2002). However, the hyperprolificity of sows resulting from the intense selection of superior maternal line genetics made the transfer of nutrients from dam to offspring a major challenge due to the greater number of piglets (Oliviero, 2022). These nutrients play a role in immune development and antioxidant activity, being crucial to increasing the resilience of piglets against diseases. 

Some micronutrients can be absorbed by piglets easily via the placenta and colostrum, but some vitamins and trace minerals need to be supplemented (Mahan & Vallet, 1997). Vitamins are serious candidates for disease resistance due to their participation in several pathways of antioxidant capacity, control of detrimental intermediate metabolites, gut microbiota diversity, regulation, and development of innate and acquired immune responses (Lauridsen, Matte, et al., 2021). It has been demonstrated that the supplementation of vitamins A and D (along with copper) to sows from one week before parturition until weaning affected the microbiota of weanling piglets and improved the homogeneity of birth weight (Galiot et al., 2021). On the other hand, in the same study, the direct oral supplementation to piglets on days 2 to 8 of age had few effects, although the exposure to UVB light and vitamin D supplementation given to sows or directly to piglets improved vitamin D status. Another study showed that the treatment of sows from mating until the weaning of their offspring with 200 mg of vitamin E and 0.3 mg of organic selenium in the diet elevated the concentrations of selenium and alpha-tocopherol in the plasma of piglets, affected the concentrations of milk and sow plasma immunoglobulins, enhanced piglets’ cell-mediated immune responses, and reduced inflammatory responses at weaning (Lauridsen, Schönherz, et al., 2021). 

Very little is known about the need for vitamin supplementation during pre-weaning. Throughout this period, the stresses of weaning outweigh the beneficial effects of lactation in response to sow supplementation. The influence of the transfer of nutrients from dam to piglet is practically over at weaning, which means that oral supplementation of vitamins directly to piglets seems to be more beneficial in this phase. High-performance piglets produce greater amounts of homocysteine, an extremely detrimental metabolite produced in large amounts by pigs, which makes them immunologically fragile (Giguère et al., 2008). The supplementation of vitamin B12 and folic acid to sows and the direct administration of vitamin B12 to weaned piglets proved to be effective in reducing homocysteine levels (Audet et al., 2015). Verso et al. (2020) evaluated the connection between homocysteine and the administration of antibiotics in weaned piglets. A reduction in homocysteine levels was observed, although it was related to an increased synthesis of vitamin B6 by the intestinal microbiota in response to antibiotic use instead of the increase of folic acid and vitamin B12 levels. Thus, it was concluded that vitamin B6 may be related to the mechanism of the action of antibiotics and that its administration may therefore be beneficial.

Tryptophan is another amino acid of great importance for protein deposition, which is transformed into several intermediate metabolites of nicotinamide (vitamin B3) when oxidized. Piglets are quite efficient at producing nicotinamide by tryptophan supplementation from 4 months of age. The catabolites of nicotinamide have beneficial effects on the immune competence of pigs. However, the intense use of tryptophan to enhance protein deposition limits its oxidation for nicotinamide formation. As pietrain pigs are more efficient in protein deposition from tryptophan, they need more vitamin B3 in the diet to maximize their robustness after weaning in relation to duroc pigs (Le Floc’h et al., 2017).

Beyond reproduction and growth, there are other aspects, such as immunocompetence, that are of major importance in pig production. Despite the great progress that has been made in pig performance during the last decades, many outbreaks of major diseases have occurred, challenging the piglet’s robustness. The supplementation of some nutrients, such as vitamins and trace minerals, to sows from gestation to weaning, or even directly to piglets, can improve immune competence and antioxidative capacity, and control intermediary detrimental metabolites for the production of healthier piglets.