What substance is introduced to axenic animals to normalize gut physiology?

The Schaedler cocktail is a specific combination of microbial organisms that is commonly used to inoculate axenic (germ-free) animals in order to establish a more normal gut microbiota and promote healthy gut physiology. Axenic animals lack any microbiota, which can lead to various physiological abnormalities. By introducing the Schaedler cocktail, researchers aim to mimic a natural gut environment, correcting deficiencies in gut flora that are critical for digestion, immune system development, and overall health.

The other options, while relevant to discussions about microbial health, do not serve the same function as the Schaedler cocktail. Probiotic solutions usually contain beneficial bacteria aimed at supporting gut health but are not standardized in the same manner for experimental use as the Schaedler cocktail. Antibiotic mixtures would typically suppress microbial growth rather than normalize gut physiology. Yeast cultures can influence gut flora but do not provide the diverse bacterial populations required to effectively simulate a normal gut environment in axenic animals. Thus, the Schaedler cocktail is the most appropriate choice for this context.