Betaine is a trimethylglycine derivative that participates in epigenetic processes, especially the methylation of deoxyribonucleic acid (DNA) and histones. The betaine or choline in the diet will be oxidized to betaine, methyl group will be provided to homocysteine, which will be converted into methionine.

The role of betaine in pig feed is to reduce the maintenance energy requirements of animals. The hypothesis for this observed effect is that when betaine can maintain intracellular osmotic pressure, the demand for ion pumping is reduced, which is an energy-requiring process. Therefore, in the case of limited energy intake, the supplementary effect of betaine is expected to be more obvious, because it increases the energy required for growth, rather than maintenance.

Betaine not only plays a role in osmotic protection in animals. In addition, many bacteria can accumulate betaine through transportation from the environment. There are indications that betaine can have a positive effect on the bacterial population in the gastrointestinal tract of weaned piglets. The total number of ileal bacteria, especially bifidobacteria and lactobacilli increase dramatically. In addition, fewer enterobacteria are found in feces. Supplementing the diet with 2500 mg/kg betaine is more effective than 1250 mg/kg in reducing the rate of diarrhea. However, the performances of weaned piglets are similar at the two supplement levels. Other researchers have shown that when betaine is added at 800 mg/kg, the rate and incidence of diarrhea in weaned piglets is lower.