Physiological and behavioral traits in female guinea pigs: estrous cycle effects and repeatability

The estrous cycle of female guinea pigs is characterized by a spontaneous ovulation and a subsequent active luteal phase that is physiologically well described. In contrast to other rodents, however, the effects of the cycle on stress responses and behavior are understudied in this species. This study examines the extent to which cortisol concentrations and behavior differ between the estrus and diestrus phases of two consecutive cycles in twelve female guinea pigs. In addition, the parameters were analyzed regarding repeatability to determine how far both physiological parameters and behavior are individually consistent throughout the cycle. Saliva samples to analyze cortisol concentrations were collected before and after a 15-minute dark-light test. The dark-light test and a 15-min sociality test were performed to analyze exploration, anxiety, and social interest. Cortisol concentrations were increased in estrus compared to diestrus. In the dark-light test, the cycle phase had no significant influence on locomotion or anxiety-like behavior. Locomotion and time spent with a conspecific in the sociality test were partly increased in estrus compared to diestrus. All behaviors were repeatable throughout the two investigated cycles. The results show that the estrous cycle of female guinea pigs can influence physiology and behavior to some extent, but that individual differences have a stronger influence on behavior than does the cycle. These findings contribute to the general understanding of physiological and behavioral changes during the estrous cycle, which are understudied not only in guinea pigs but in many mammalian species.