Functional amino acids & intestinal health in weaned piglets

Functional amino acids and the relationship with intestinal health in weaned piglets

Enteric diseases in weaned piglets limit the expression of animals’ true genetic potential, by causing negative impacts on the integrity of the intestinal mucosa which impairs its ability to absorb nutrients efficiently(Eriksen et al., 2019).

In most production systems, the prevention and treatment of piglets’ gastrointestinal diseases, is mainly carried out through the use of antibiotics.

Besides their implementation for therapeutic purposes, some antibiotics are used as performance enhancers. This scenario can result in the appearance of pathogenic bacteria that acquire resistance to commonly used active principles. Posing serious health risks for both animals and humans worldwide. This significant health concern has led to bans on antibiotic use in several countries (Albernaz-Gonçalves et al., 2021).

Therefore, different nutritional strategies have been developed to replace antibiotic growth promoters while mitigating the negative effects of enteric diseases on the performance of weaned piglets. Among these, we can highlight the use of functional amino acids such as tryptophan, threonine and glutamate. These help improve intestinal health and consequently, overall productive performance.

This review aims to demonstrate the beneficial effects of functional amino acids such as tryptophan, threonine and glutamine on the intestinal health of weaned piglets.

Weaning and its effects on gut health

Weaning tends to reduce piglet’s immune response, affecting its efficiency and making them more susceptible to viral and bacterial infections. Under such conditions of reduced immunological activity, the onset of diseases increases significantly. An example of this, is a higher incidence of gastrointestinal diseases with diarrhea as a major clinical sign. Which hamper zootechnical performance significantly. [register]

Intestinal disorders compromise intestinal integrity and permeability. Causing morphological and physiological alterations that promote villous atrophy and crypt hyperplasia, which interfere with adequate nutrient digestion and absorption. Thereby reducing the efficiency of intestinal function(Xiong et al., 2019).

Piglets exhibit a significant reduction in feed intake levels due to an abrupt dietary change during the first days post weaning. Considering the fact that they are forced to transition from a liquid diet to a solid one, favoring intestinal dysbiosis and other changes within the intestinal environment. As there is sudden absence of substrate for the development and function of the intestine and its microbial population.

The stress caused by weaning represents a significant immune challenge for the piglet’s organism. Demanding an important amount of nutrients, which are used to fuel immune cells participating in the recovery of damaged tissues and in the restoration of intestinal homeostasis (Li et al., 2018).

• Weaned piglets are also subjected to physiological, structural and functional changes, which interfere with the activity of: endogenous enzymes, absorption processes, secretion processes and intestinal barrier functioning.  The intestinal epithelial barrier is responsible for preventing pathogen invasion and translocation. Avoiding the damage of intestinal integrity through the expression of transmembrane proteins with narrow junctions, such as occludin and claudin.

Intestinal permeability increases with barrier disruptions, allowing the penetration of pathogenic bacteria, antigens and toxins, which result in: inflammation, inefficient nutrient absorption,a higher incidence of diarrhea and a reduction in overall animal performance (Moeser et al., 2017)..

Functional amino acids are referred to as such, because they exert effects on intestinal microbiota composition, as well as offering nutritional benefits to the animal. Some of their functions are: 

The supplementation of certain functional amino acids, such as tryptophan, threonine and glutamine as a means to help maintain animal health levels under important challenges like weaning, is a highly recommended nutritional strategy. (Le Floc’h et al., 2018).

Studies reveal that functional amino acids can provide extra energy inputs to the intestinal epithelium. Contributing towards intestinal development, regulating immunity, epithelial barrier function, as well as modulating the composition of intestinal microbiota by favoring its colonization with beneficial microorganisms(Kim and Duarte, 2021).

These are also related with the supply of energy to enterocytes, which are responsible for nutrient absorption and intestinal barrier permeability. Hence, their correct inclusion contributes to improving the use of dietary nutrients and favors the animal’s development (Chalvon-Demersay et al., 2021).

When evaluating tryptophan supplementation at 0.2 and 0.4% in weaned piglet diets, researchers observed a reduction in the abundance of pathogenic bacteria such as Clostridium sensu stricto and Clostridium XI. As well as observing increased numbers of beneficial bacteria from the genera Prevotella, Roseburiae and Succinivibrio.

Pathogenic bacteria are responsible for many intestinal disorders. The reduction pathogenic bacterial populations with the dietary inclusion of tryptophan, reveal an inhibitory effect associated with this amino acid. The beneficial bacteria mentioned above belong to the phylum Bacteroidetes and Firmicutes. These are considered as short-chain fatty acid producers, which have the ability to regulate intestinal homeostasis (Liang et al., 2018).

Tossou et al. (2016) evaluated the effects of dietary L-tryptophan supplementation by subjecting animals to three levels of L-tryptophan (0.0, 0.15  , and 0.75%).  After concluding this study, researchers did not observe significant results regarding animal performance (average daily gain, average daily intake and feed conversion).

Threonine is also associated with adequate gastrointestinal function in piglets, as it improves mucosa and intestinal barrier stability.

This amino acid is involved in the synthesis of mucin, a glycoprotein that helps protect the intestine from excess enzymatic activity and hydrochloric acid. As well as providing a physical barrier that prevents the penetration of pathogens that can damage the intestinal mucosa. These effects, make threonine essential for the maintenance of structural homeostasis and intestinal morphology (Zhang et al., 2019).

Dietary L-threonine supplementation positively influenced gut vitality and mucin synthesis in weaned piglets, as animals supplemented with L-threonine (2.0 g/kg of diet) were found to achieve significant results for intestinal integrity, with reduced inflammatory responses (Zhang et al., 2019).

Mao et al. (2019) evaluated the effects of threonine supplementation on mucin production in  weaned piglets. They assessed two levels of supplementation, 0.74% and  0.89%, and found that animals supplemented with 0.89% presented an increase in mucin production. They suggested that this can improve intestinal barrier integrity.

Glutamine is associated with an effective proliferation of intestinal cells and lymphocytes, which corroborates its importance for the gastrointestinal tract and the immune system (Ma et al., 2021). It also promotes stability in intestinal morphology, by preventing villous atrophy and ensuring adequate growth.  Glutamines contributes to enhancing immune function, especially under inflammatory processes caused by enteric pathogens, such as Escherichia Coli (Ji et al., 2019).

Luise et al. (2022) evaluated glutamine (Gln) supplementation associated with glutamate (Glu). Assessing its influence on weaned piglets’ gut health. They concluded that the association of both amino acids at the following ratios: 25:75 and 50:50 (Glu:Gln) benefited immune function and the intestinal barrier. Eminent growth of goblet cells was observed in the jejunum at the 50:50 (Glu:Gln) ratio, contributing to restore piglets’ intestinal health.

The supplementation of functional amino acids such as tryptophan, threonine and glutamine in weaned piglet diets may attenuate some of the negative impacts of weaning. Improvements in: intestinal mucosa integrity, colonization of beneficial microorganisms and in the efficiency of the intestinal barrier, are all beneficial effects obtained through the use of functional amino acids.