What is the cause of a low litter size in axenic gerbils?

• A. Lower level of hormones
• B. Reduced milk capacity of the female
• C. Enlarged cecum in the axenic animals
• D. Lower sperm production in the male

Answer: (C)

The main idea here is how gut microbiota absence affects energy balance and reproduction. In axenic (germ-free) gerbils, the cecum becomes enlarged because there’s no bacterial fermentation to help process fibers and regulate gut contents. This enlarged cecum reflects altered gut physiology and shifts in energy use. Reproduction and lactation in small mammals require a steady energy supply, and energy may be diverted to maintaining the enlarged gut and dealing with altered nutrient absorption, leaving less energy for fetal development and milk production. That reduced energy availability can lead to smaller litter sizes. Other factors like hormones, the female’s milk capacity, or male sperm production aren’t directly tied to the germ-free condition in a way that would explain the observed litter reduction.