Nearly every facet of an organism's life, beginning with the formation of gametes and progressing through conception, prenatal and postnatal development, aging, morbidity, and death, is affected in one of several ways by temperature. The thermoregulatory system must adapt over the continuum of morphological and physiological changes in life in order to efficiently maintain thermal homeostasis. There also are critical periods in development during which the thermoregulatory system is extremely vulnerable to environmental perturbations, thereby creating unstable conditions for other homeostatic processes. The purpose of this chapter is to discuss the effects of environmental temperature and body temperature on crucial developmental aspects of laboratory rodents, including growth, reproductive function, prenatal and postnatal development, and aging.

Optimal thermal conditions for growth

The thermal limits for optimal growth are key variables in successful management of animal colonies. It is important to know how various aspects of growth and development, such as weight gain, organ development, fertility, fecundity, and fetal development, are affected by subtle changes in environmental temperature. That is, do these variables have a zone of thermoneutrality (see Chapter 3) or a range of ambient temperatures in which their functioning and development are optimal? Furthermore, does the optimal temperature for a given variable change with age? Are the optimal zones of development equivalent between species?