To maintain a healthy gut is definitely key for a pig to digest and absorb dietary nutrients efficiently. A balanced microbiota (i.e., a healthy micro-ecosystem) is an indispensable constituent of a healthy gut. Probiotics, the live microorganisms which, when administered in adequate amounts, confer good health benefits onto the host, are a category of feed additives that can be used to replenish the gut microbial population while recuperating the host immune system. Besides their antitoxin and diarrhea reduction effects, dietary supplementation of probiotics can improve gut health, nutrient digestibilities and, therefore, benefit nutrient utilization and growth performance of pigs. Current knowledge in the literature pertinent to the beneficial effects of utilizing various probiotics for swine production has been comprehensively reviewed, and the safety and the risk issues related to probiotic usage have also been discussed in this paper. Considering that the foremost cost in a swine operation is feed cost, feed efficiency holds a very special, if not the paramount, significance in commercial swine production. Globally, the swine industry along with other animal industries is moving towards restricting and eventually a total ban on the usage of antibiotic growth promoters. Therefore, selection of an ideal alternative to the in-feed antibiotics to compensate for the lost benefits due to the ban on the antibiotic usage is urgently needed to support the industry for profitable and sustainable swine production. As is understood, a decision on this selection is not easy to make. Thus, this review paper aims to provide some much needed up-to-date knowledge and comprehensive references for swine nutritionists and producers to refer to before making prudent decisions and for scientists and researchers to develop better commercial products.

Improving feed efficiency of pigs with dietary application of amino acids (AAs) is becoming increasingly important because this practice can not only secure the plasma AA supply for muscle growth but also protect the environment from nitrogen discharge with feces and urine. Lysine, the first limiting AA in typical swine diets, is a substrate for generating body proteins, peptides, and non-peptide molecules, while excess lysine is catabolized as an energy source. From a regulatory standpoint, lysine is at the top level in controlling AA metabolism, and lysine can also affect the metabolism of other nutrients. The effect of lysine on hormone production and activities is reflected by the change of plasma concentrations of insulin and insulin-like growth factor 1. Lysine residues in peptides are important sites for protein post-translational modification involved in epigenetic regulation of gene expression. An inborn error of a cationic AA transporter in humans can lead to a lysinuric protein intolerance condition. Dietary deficiency of lysine will impair animal immunity and elevate animal susceptibility to infectious diseases. Because lysine deficiency has negative impact on animal health and growth performance and it appears that dietary lysine is non-toxic even at a high dose of supplementation, nutritional emphasis should be put on lysine supplementation to avoid its deficiency rather than toxicity. Improvement of muscle growth of monogastric animals such as pigs via dietary lysine supply may be due to a greater increase in protein synthesis rather than a decrease in protein degradation. Nevertheless, the underlying metabolic and molecular mechanisms regarding lysine effect on muscle protein accretion merits further clarification. Future research undertaken to fully elucidate the metabolic and regulatory mechanisms of lysine nutrition could provide a sound scientific foundation necessary for developing novel nutritional strategies to enhance the muscle growth and development of meat animals.

Gut health has significant implications for swine overall health status and nutrient utilization, due to its various functions including digestion and absorption of nutrients, secretion of mucins and immunoglobulins, and selective barrier protection against harmful antigens and pathogens. Both the basic anatomical structure of the gut (such as epithelial cells) and its luminal microbiota play important roles for maintaining gut health and functions. The interactions between epithelial cells and luminal microbiota have significant impact on host nutrition and health through the metabolism of dietary components. Amino acids, which are major nutrients for pigs, are not only obligatory for maintaining the intestinal mucosal mass and integrity, but also for supporting the growth of microorganisms in the gut. Dietary amino acids are the major fuel of the small intestinal mucosa. Particularly, glutamate, glutamine, and aspartate are the major oxidative fuel of the intestine. Emerging evidence shows that arginine activates the mTOR signaling pathway in the small intestine. Utilization of glycine by the small intestinal mucosa to synthesize glutathione is a very important physiological pathway, and the role of glycine as a powerful cytoprotectant has also been recognized. The major end products of methionine and cysteine metabolism are glutathione, homocysteine and taurine, which play important roles in the intestinal immune and anti-oxidative responses. Threonine is highly utilized by the gut and is particularly important for mucin synthesis and maintenance of gut barrier integrity. Moreover, either a deficiency or an excess of dietary threonine can reduce the synthesis of intestinal mucosal proteins and mucins in young pigs. Various new functions of amino acids on gut health and functions have been discovered in recent years. Thus, this review is to provide some up-to-date knowledge for industry application of dietary amino acids in order to enhance swine gut health and functions, and also it is to provide a comprehensive reference for further scientific research in this regard.

Advances in nanotechnology have permitted molecular-based targeting of cells through safe and biocompatible magnetic nanoparticles (MNP). Their use to detect and remove damaged spermatozoa from semen doses could be of great interest. Here, MNP were synthesized and tested for their ability to target apoptotic (annexin V) and acrosome-reacted (lectin) boar spermatozoa, for high-throughout retrieval in a magnetic field (nanoselection). The potential impacts of nanoselection on sperm functions and performance of offspring sired by sperm subjected to nanoselection were determined. Fresh harvested and extended boar semen was mixed with various amounts (0, 87.5, and 175 μg) of MNP-conjugates (Annexin V-MNP or Lectin-MNP) and incubated (10 to 15 min) for 37 °C in Exp. 1. In Exp. 2, extended semen was mixed with optimal concentrations of MNP-conjugates and incubated (0, 30, 90, or 120 min). In Exp. 3, the synergistic effects of both MNP-conjugates (87.5 μg – 30 min) on spermatozoa was evaluated, followed by sperm fertility assessments through pregnancy of inseminated gilts and performance of neonatal offspring. Sperm motion, viability, and morphology characteristics were evaluated in all experiments. Transmission electron microscopy, atomic force microscopy, and hyperspectral imaging techniques were used to confirm attachment of MNP-conjugates to damaged spermatozoa. The motility of nanoselected spermatozoa was improved (P < 0.05). The viability of boar sperm, as assessed by the abundance of reactive oxygen species and the integrity of the acrosome, plasma membrane, and mitochondrial membrane was not different between nanoselected and control spermatozoa. The fertility of gilts inseminated with control or nanoselected spermatozoa, as well as growth and health of their offspring were not different between (P > 0.05). The findings revealed the benefit of magnetic nanoselection for high-throughput targeting of damaged sperm, for removal and rapid and effortless enrichment of semen doses with highly motile, viable, and fertile spermatozoa. Therefore, magnetic nanoselection for removal of abnormal spermatozoa from semen is a promising tool for improving fertility of males, particularly during periods, such as heat stress during the summer months.