The role of short and medium chain fatty acids on intestinal health in piglets

The problem of postweaning diarrhoea still has a great practical importance for piglet producers, it causes suffering and losses of animals and can have substantially negative effects on profitability due to lower performance and feed conversion. Enterotoxic Escherichia coli strains are the main cause of post weaning diarrhoea and it has become obvious, that their effects on the gut can be counteracted by optimized feed formulations. In the meantime, after the ban of antibiotic growth promoters, a wide spectrum of nutritional strategies exists to better deal with the problem of digestive disorders under practical conditions. Amongst optimized diet formulation, feed additives are increasingly considered as alternative to classical antibiotics, although their “antimicrobial” effect is probably not the only mode of action when included in usual concentration in the diet, they may act more as “microbiome regulators”. In many studies, it has been found that their use can have a positive effect on animal performance, probably because they affect gut function and intestinal health.

Short chain fatty acids (SCFA) with 1-4 carbon atoms and their salts play an important role, their use in piglet feed is quite common. In contrast to the free acids, the salts of organic acids are odourless, have a low volatility and a higher water solubility. The addition of salts is easier to handle in animal feed production compared to the free acids.

Medium chain fatty acids (MCFA) are used as free acids, as triglycerides and as salts of fatty acid distillates. Medium chain fatty acids are naturally found as part of triglycerides in milk fat and in various vegetable fats such as coconut and palm kernel oil and in Cuphea seed oil.

Interestingly, the exact mode of action of short and medium chain acids is still scientifically debated. It seems multifactorial and depends on the dietary concentration, the feed composition and the specific microbiome situation in farms, which is an important but still largely unknown factor.

Various studies have shown that the antibacterial effects of short and medium chain fatty acids are particularly relevant at low pH levels in the digesta. Both, short and medium chain fatty acids are weak organic acids, i.e. at higher pH values they are predominantly present as salts, which reduces their penetration through the bacterial cell wall. This is considered as important prerequisite for their efficacy against bacteria. Lowering the pH inside the bacterial cell causes irreversible damage to important bacterial enzymes, which can lead to growth inhibition or death of the bacteria.

Various studies have shown that the use of short and medium chain fatty acids and triglycerides can actually lead to a significant reduction of diarrhoea in the post-weaning phase of piglets. It can be assumed that the stabilizing effects of organic acids in the digestive tract is already effective in the upper digestive tract, i.e. in the stomach. The medium chain fatty acids with 6-12 carbon atoms have an antibacterial effect, if the concentrations in the feed are correspondingly high. Triglycerides with medium-chain fatty acids have shown effects on the health of piglets and their intestinal microbiota in both, the stomach and small intestine. In addition to the effects of fatty acids on the intestinal microbiota and on intestinal health, they are interesting substrates for the intermediary metabolism in piglets. It was shown, for example, that butyric acid is an important substrate for the energy metabolism of enterocytes.

Medium chain fatty acids are absorbed quickly and independently of bile secretion and can be utilized in intestinal tissues and in the liver for energy production. The rapid absorption of short and medium chain fatty acids has initiated an interesting development that has led to “protected” or “encapsulated” acids. The aim is to achieve greater efficiency in the lower sections of the digestive tract, which has been shown in various studies.

The impact of medium chain fatty acids, which has been less intensively studied compared to the short chain fatty acids, is summarized in table 1.

Table 1: Nutritional and physiological effects of medium chain triglycerides (MCT) and fatty acids in piglets (Zentek et al. 2011)

The majority of the published work clearly shows that the use of fatty acids in pigs has health benefits, that some of them also have a preservative effect on the feed and that the performance of the animals is generally positively influenced. As a result, they are now firmly established in the spectrum of the animal feed industry.