The central role of intestinal health on the effect of feed additives on feed intake in swine and poultry

Additives are commonly added to animal diets to stimulate production performance, and to improve welfare and health especially in stressful periods of life. The higher production performance generally will be a result from a higher feed intake, better digestion and absorption of nutrients, from improved intestinal health or resilience against systemic challenges or a combination thereof. Many feed additives have a direct or indirect effect on improving the integrity of the intestinal epithelium and on the amount of fermentable substrate available for the intestinal microflora. The mechanism by which these effects influence feed intake are discussed in general terms. Due to the wide variety of modes of actions by which feed additives can stimulate feed intake (by improving intestinal integrity, preventing intestinal damage, compensating for additional nutritional requirements for immune response, reducing the amount of substrate for the microflora or preventing inflammation) or reduce feed intake (by the addition of feed enzymes to improve dietary energy value or feed refusals due to organoleptic problems associated with the addition of medium chain fatty acids and organic acids at high inclusion levels) it is difficult to conclude on general effects. Moreover, since different additives might partially have similar effects, it can be expected that these effects are not additive. The direct or indirect effects of specific feed additives such as pro- and prebiotics, medium chain fatty acids, mycotoxin binders, organic acids, amino acids, emulsifiers, enzymes, anticoccidials, phytogenic compounds on affecting feed intake in swine and poultry species are separately discussed.