Reduced maintenance energy
Not only an increased digestibility can explain the reported improved growth performance and feed conversion in pigs supplemented with dietary betaine. Incorporation of betaine in pig diets also leads to a reduction in the maintenance energy requirement of the animal. Hypothesis for this observed effect is the reduced need for ion pumping, an energy requiring process, when betaine is available for maintaining the intracellular osmolarity. Under conditions where energy intake is limiting, effects of betaine supplementation are therefore expected to be more pronounced, by increasing the availability of energy for growth instead of maintenance.
The epithelial cells lining the intestinal wall, need to cope with highly variable osmotic conditions, generated by the luminal content during nutrient digestion. Meanwhile, these enterocytes need to control the exchange of water and different nutrients between the intestinal lumen and the plasma. To protect the cells against these challenging conditions, betaine is an important organic osmolyte. When looking at the betaine concentrations in different tissues, the intestinal tissue contains considerably high betaine levels. Moreover, it was observed that these levels can be influenced by dietary betaine concentration. Well balanced cells will have a better proliferation and good resilience. Accordingly, researchers found that increasing betaine levels in piglets increased duodenal villus height and ileal crypt depth, and that the villi were more uniform.
In another study an increased villus height could be observed in duodenum, jejunum and ileum, without influence on the crypt depth. The protective effects of betaine on intestinal structure might be even more important under specific (osmotic) challenges, as observed in broilers infected with coccidia.
Gut barrier effect
The intestinal barrier mainly consists of epithelial cells, attached to each other by tight junction proteins. The integrity of this barrier is fundamental to prevent the entry of harmful substances and pathogenic bacteria that otherwise will cause inflammation. In pigs, a negative effect on the gut barrier is recognised as a result of mycotoxin contamination of feed, or as one of the negative impacts of heat stress.
To measure the influence on the barrier effect, in vitro tests on cell lines, measuring the trans-epithelial electrical resistance (TEER), are often used. With the application of betaine, an improved TEER could be observed in multiple in vitro experiments. When cells are exposed to high temperatures (42°C), there is a decrease in TEER (Figure 2). The addition of betaine in the growth medium of these heat exposed cells, counteracted the decreased TEER, indicating an improved heat resist-ance. Additionally, in vivo research in piglets, measured an increased expression of tight junction proteins (occludin, claudin1 and zonula occludens-1), in the jejunal tissue of animals on a diet with 1,250 mg/kg betaine compared to control. Also, the marker for intestinal mucosal injury, diamine oxidase activity in plasma of these pigs was significantly lower, indicating a stronger gut barrier. When betaine was supplemented to the diet of growing finishing pigs, an increased gut tensile strength was measured at slaughter.