Physiological additives are those that help the normal development of physiological functions of animals or that make up for their deficiencies. Among these, acidifiers, Yucca schidigera extracts and fructo-oligosaccharides (FOS) have to be considered. Acidification is crucial in young animals, which cannot secrete enough hydrochloric acid for a correct protein digestion. Numerous studies have shown that inorganic-based acidifiers are the most appropiate to achieve not only a regular digestion, but improvements in health and performances. Yucca extracts are used as dietary supplements for any animal species, primarily for ammonia and odor control, thus improving environmental conditions and, consequently, health and performances. In ruminants, Yucca extracts improve nitrogen utilization through their antibacterial and antiprotozoal function, favoring the activity of beneficial bacteria. Finally, FOS act also benefitting the saprofitic flora in detriment of the pathogenic flora, thus improving health and performances both in young and adult animals.