Gut health, a key factor
In 2010, FAO, OIE and WHO formally joined with the aim of working together to prevent and control risks to human, animal and ecosystem health. This idea is based on the “One Health” concept, which was defined more than a century ago as the connection between human health, animal health and environmental health, being interdependent.
The fight against bacterial resistance to antimicrobials is one of the priorities being tackled worldwide, with policies to reduce the use of antibiotics in both human medicine and animal health. Thus, in animal production we started with the ban on the use of antibiotic growth promoters (AGP) in the EU with directive 1831/2003, followed by several directives aimed at reducing the use of antibiotics in general in production animals.
Adapting to these changes requires a continuous improvement in the knowledge of the health and nutrition of our animals. This is where the gut has taken centre stage, being a key player in the digestion and absorption of nutrients, but also in the immune system and health of animals. We now know that the gut has its own important nutrient requirements and that its flora plays a key role in digestion, but also in the development of the immune system itself. Thus, good animal health starts with good gut health.
Piglets at weaning, a critical stage
Weaning is one of the critical stages in pig production, and it is a crucial time for the gut of piglets, which are subjected to an abrupt change of diet and environment. This leads to multiple alterations at intestinal level, from epithelial alteration and inflammation to dysbiosis, and often triggers the diarrhoeal processes typically found at this stage.
To avoid these diarrhoeal processes, antibiotics and other antimicrobials such as zinc oxide have been key in piglet weaning. These molecules, with different antimicrobial, anti-inflammatory and immunomodulatory effects, have modulated and improved the intestinal environment, but also its nutritional requirements.
Thus, we now know that the requirements for certain amino acids are higher in animals fed without AGP, as it has been shown for threonine and tryptophan. Recently, Ren et al. (2021) have also shown in a new study that the requirements for total sulphur amino acids (TSAA), methionine and cysteine are higher in piglets weaned on antibiotic-free diets.
The importance of methionine in piglets’ gut health
Methionine plays a basic role in the nutrition of monogastric animals, being considered the second or third essential amino acid in piglet diets. Methionine, apart from protein synthesis, is involved in several basic metabolic functions important for animal health (methyl group donor, antioxidant effects, precursor of glutathione peroxidase (GSH) and taurine).
On the other hand, 20% of methionine and 25% of cysteine ingested through the diet are metabolised in the gut itself, and these sulphur amino acids are important for intestinal mucosal growth in piglets (Bauchart-Thevret et al., 2009). Thus, Zong et al. (2018), demonstrated how increasing the ratio of sulphur amino acids above the requirements (NRC, 2012) in the diet of piglets supplemented with methionine improved performance, intestinal morphology and intestinal enzyme activity in the animals.
Based on the importance of methionine at intestinal level, in a recent study Ren et al (2021) wanted to study how weaning piglets without antibiotics can affect sulphur amino acid requirements. In this study, they conclude that when AGP are used in piglets’ diets, a ratio of 51% TSAA:Lys is sufficient to cover animals’ requirements, while in the absence of antibiotics, this ratio rises to 66% TSAA:Lys to obtain the same productive results.
Therefore, formulating antibiotic-free diets for piglet at weaning, as with other amino acids, appears to require an increase in Methionine to maintain productive performances and improve gut health.
L-Methionine helps to improve intestinal morphology in piglets at weaning
There are different sources of methionine available on the market for animal nutrition, MHA, DL-Methionine and L-Methionine. L-Methionine is the only source of methionine obtained through a fermentation process, being the only one 100% biologically active after ingestion, the others require metabolic modifications to be effective as source of methionine for the animal.
Figure 1. Excretion of methionine in broilers depending on the source used. Adapted from Saunderson et al., 1985.
As early as 1985, Saunderson et al. carried out studies to determine the retention of different sources of methionine in broilers. They radioactively marked the three sources of methionine used (DL-HMTBA, DL-Met and L-Met), and found that excretion was significantly different: 10% of the DL-Met administered was excreted, while in the case of DL-HMTBA excretion increased to 21% of product administered. In contrast, only 2% of the administered L-Met was excreted (Fig. 1).
Figure 2. Intestinal villus length in piglets supplemented with DL-Methionine (DLM) and L-Methionine (LM). Adapted from Shen et al., 2014.
Similarly, Shen et al. (2014), conducted a study to compare DL-Methionine and L-Methionine as sources of methionine in piglets at weaning, and to study possible differences in gut health. In this case, animals fed L-Methionine showed an increase in intestinal villus length (Fig. 2), together with an increase in duodenal GSH content (Fig. 3) and total antioxidant capacity (TAC) at the intestinal level (Fig.4).
Figure 3 and 4. GSH and TAC content in the duodenum of piglets supplemented with DL-Methionine (DLM) and L-Methionine (LM). Adapted from Shen et al., 2014.
Conclusions
Formulating antibiotic-free diets for piglets at weaning, and soon zinc oxide-free diets, make it necessary to review upwards the levels of sulphur amino acids, given their important functions at intestinal level. Oxidative stress, inflammation and loss of epithelial integrity during weaning make methionine a key amino acid for piglets’ gut health at this stage.
On the other hand, the source of methionine used in the diet can be decisive at this stage. L-Methionine supplementation in piglets at weaning has been shown to improve duodenal morphology and reduce oxidative stress, improving GSH synthesis in the gut mucosa compared to DL-Methionine supplementation. Consequently, L-Methionine is a methionine source of choice for piglets at weaning.
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