Which of the following correctly describes a feature of caging systems?

The feature of caging systems that allows for normal movement and posture is fundamental to the well-being of laboratory animals. It is crucial that cages are designed to accommodate the physical needs of the animals housed within them. This includes providing sufficient space for animals to stand, lie down, turn around, and engage in natural behaviors. When cages allow for normal movement and posture, they contribute to the animals' physical health and mental well-being.

Animal welfare guidelines emphasize the importance of providing an environment that meets the behavioral and physiological needs of the species being housed. Ensuring adequate space is a key aspect of promoting the welfare of laboratory animals. This feature of caging systems directly supports the overall goal of humane and ethical treatment in research settings.

In contrast to this correct choice, acknowledging the other options demonstrates an understanding of the importance of cage design and function. Unsanitary conditions are detrimental but do not define an essential feature of caging systems; thus, the statement regarding unsanitary cages does not encapsulate the goal of a well-designed cage. The notion that cages are optional contradicts established animal welfare guidelines, which typically mandate housing; similarly, the idea that cages are mandatory but without requirements undermines the specific needs of the animals involved in research.