INDIRECT EFFECTS OF BUTYRATE

( I ) . INCREASED PANCREATIC ACTIVITY.

The pancreas, with its dual endocrine and exocrine function, plays a critical role in digestion. Focusing on the exocrine function, this is triggered by the presence of food in th e digestive tract, which produces a hormonal response that activates the production of digestive enzymes in the pancreas. The main ones are lipases, amylases and proteases, so we are talking about enzymes that carry out the digestion of ingested food and m ake it available to be absorbed along the digestive tract. Therefore, optimal pancreatic activity will improve animal performance, while a pathological situation, such as underdevelopment in chickens as a result of hatchery problems, will limit ration utilization.

Butyrate is an additive that can influence the regulation of pancreatic activity. Butyrate, as is well known, has a positive effect on nutrient digestibility, improving ration utilization and technical parameters of the animals (Guilloteau et al., 2010; Mallo et al., 2011). These are largely due to the effect of this additive on intestinal morphology, since it has a trophic effect on enterocytes that improves their absorption capacity. In addition to this, there is an indirect effect on the availab ility of nutrients in the digestive tract, which makes it possible to better explain the improved performance of the animals.

The effect is indirect because we observed it on enterohormones which in turn stimulate pancreatic secretion and therefore the pre sence of digestive enzymes in the intestine. The main of these enterohormones is cholecystokinin (CCK), which stimulates the exocrine cells of the pancreas and whose concentration increases with the addition of butyrate in the diet in mammals (Kotunia, 200 4; Guilloteau, 2010b). In birds, upregulation of preprocholecystokinin, a gene involved in CCK regulation, has been observed (Moquet, 2018). The increase in this enterohormone has been attributed to the presence of FFAR3, short - chain fatty acid receptors, in intestinal I cells (Moquet, 2018), which are the CCK secreting cells.

The effect of CCK is twofold. On the one hand, it activates the secretion of pancreatic juice, something that has not been studied much, but whose increase by the inclusion of butyr ate in the diet has been observed in piglets (Sileikiene et al., 2005). On the other hand, it has a trophic effect on the aforementioned exocrine cells. The mitotic acceleration effect seems clear (Guilloteau, 2010), but not so much if it only promotes cel l regeneration or if it allows to increase the size of the pancreas, which would compensate an abnormally small growth of the pancreas.

In conclusion, the addition of sodium butyrate in the ration has the effect of improving the efficiency of pancreatic a ctivity. Under physiological conditions, this optimizes the utilization of dietary energy and protein. In underdeveloped pancreas conditions, it will partly compensate for the problems by maximizing cellular activity