Swine production faces constant and evolving challenges to produce pigs more sustainably, achieve higher welfare standards to meet animals needs and consumer demands as well as being cost-effective. While demands are increasing, traditional tools used to tackle production challenges—such antibiotics and therapeutic zinc oxide—are being restricted in many parts of the world due to the threat of antibiotic resistance. At the same time, advances in genetics have led to a trend of hyper prolificacy in sows, which poses additional challenges. Higher numbers of piglets born per sow per year has resulted in larger variation in piglet birthweight more metabolic challenges on the sow which, in turn, impacts the onset of colostrum and milk production, thus increasing the risk of less robust piglets at weaning and performance losses later in life.

The newly born piglet is immature in many respects and the first week of life is critical in dictating the future health and productivity outcomes of that piglet. During these first few days of life, the gut undergoes rapid development increasing both digestive and absorptive capacity. In parallel, the colonization of the gut by microbes is well underway and has a pivotal role in shaping the composition of the gut microbiome and driving the development of the gut associated lymphoid tissue (GALT) which is home to more than 70% of the piglet’s immune cells. In our search for more sustainable strategies support piglet care during early life, the most powerful weapon at our disposal is often overlooked: the piglets’ own immune competency.  

Immune competency is vital for life, but its development and use have an associated cost for all animals, especially the young. It is a delicate balance: To function effectively, the immune system should respond appropriately to the various stimuli it encounters, only mounting an immune response to genuine threats and remaining largely unresponsive to low-grade stimuli. However, in young piglets, the immune system is largely immature and unable to easily distinguish between different threat levels and responding to all as genuine threats.  In piglets, it is well known that immune competency development begins in-utero, continues with the ingestion of passive immunity received from the sow via colostrum and milk, and more recent research has demonstrated that the gut microbiome plays a pivotal role in priming the development of the gut and immune system. To best prepare piglets for the challenge of weaning and beyond, the development of immune competency should be promoted via two paths: 

1. systemically, enhancing the quality of passive immunity received from the sow, and
2. locally via modulation of the gut microbiome to prime the development of the mucosal immune system (Figure 1). 

Systemic immune competency development of a newly born piglet is highly dependent on the nutrition of the sow, starting in-utero and continuing with good quality and quantity of colostrum and milk. Therefore, a sow’s nutrition, health, and the ability to transfer it to the piglets are key to their early and robust immune system. Micronutrients including some vitamins such as D3, E, C and various B vitamins, as well as minerals are known to have immunomodulatory benefits. Piglets are born with low levels of blood vitamins and the high demands on these vitamins to support immune development and activation often result in piglets that are deficient. Considering the greater demands on the modern sow to rear a larger litter, there is a need for a more precise micro-nutrition approach to sow nutrition during late gestation and lactation to support the optimum colostrum quality and yield.

To function effectively, the systemic immune system needs to be both proficient at immune cell proliferation and regulation​ and protected from cell damage due to redox imbalance.  Vitamins E and C have long since been recognized for their ability to act as potent antioxidants that prevent oxidative damage of immune cells. Piglet viability can be enhanced through optimum vitamin E supplement of sows through gestation and into lactation (Wang et al., 2017). More recently, the role of vitamin D3 or, more importantly, its main metabolite, 25-hydroxy (OH) vitamin D3 in immunomodulation is just starting to be understood. One of vitamin D3 primary roles is not only to support the activation of immune cells and production of antimicrobial peptides but also to limit excess responses. Pigs are born with very low levels of blood 25-OH vitamin D3 which seldom reach the minimum much less the optimum range to support immunity. Now understanding the critical role of vitamin D3 in immune function, piglets can be at a disadvantage without adequate vitamin levels. Konowalchuk et al. (2013) reported that supplement of vitamin D3 and the 25-OH vitamin D3 form in particular increased immune cell number and activation in weanling pigs.

The local gut associated lymphoid tissue (i.e., gut lumen content) has a critical role to play in the defense of the piglet’s body from the outside environment. Its development is driven by the early establishment of a diverse and stable gut microbiome whose magnitude and impact are now believed to extend even beyond the gut to the development of immune tissue in other organs such as the lungs, however these mechanisms are still poorly understood. The development of the gut microbiome of piglets begins as soon as they leave the sterile conditions of the uterus and are largely influenced by the microbiome of the sow and her immediate environment. Microbial colonization tailors gastrointestinal development and modulates epithelial barrier function which is the first line of defense. Early microbial colonization also modulates innate and adaptive immune responses, thus influencing the host’s ability to mount adequate inflammatory responses and to resist disease. Developing and maintaining a stable and diverse gut microbiome is critical to pathogen resilience and optimum functioning of the gut in an environment of reduced medication. There are numerous nutritional tools available to support the development of a balanced bacterial community in the gut. The administration of probiotics such as Enterococcus faecium appears to be most successful when administered to both the sow during the end of gestation and lactation to direct early engraftment of benefit strains in the developing but still malleable gut microbiome. Another strategy to support a healthy gut microbiome of the sows and consequently benefit the piglets is by improving fiber digestibility. Xylanases increase the supply of prebiotic fibers and energy, crucial during the negative energy balance period over lactation.

To prepare piglets to overcome challenges associated with weaning and beyond, it is vital to develop immune competency as early as possible through a multi-component nutritional approach. Before birth, optimized vitamin E, C and D nutrition of sow improves the vitamin serum status of piglets at birth as well as colostrum quality resulting in better passive immunity and litter performance​. Around birth​, shaping early microbial colonization of the piglet gut with beneficial microbes such as probiotics is crucial to boosting immune competency and avoiding diarrhea​. During lactation​, ensuring the correct levels of vitamin D in sows optimizes the vitamin supply in colostrum and milk; probiotics stimulate early piglet gut colonization and reduce the incidences of diarrhea during the suckling period; and xylanases increase net energy supply via improved fiber digestibility, producing postbiotic such as short chain fatty acids, with the result of robust and heavier piglets at weaning.