Behavioral and physiological changes during the estrous cycle of socially housed female guinea pigs

The estrous cycle of female mammals does not only cause regular changes in steroid hormone concentrations but can also influence behavior and hence (social) life. A valuable model organism to study such effects is the guinea pig: its long 16-day estrous cycle with an active luteal phase represents a perfect opportunity to investigate the estrous cycle in detail, but information on estrous cycle effects is scarce. This study investigated the proestrus/estrus and diestrus phases of two consecutive cycles in twelve socially housed female guinea pigs. Following cycle monitoring, sociopositive and aggressive behavior, general activity patterns, anxiety-like behavior, and saliva cortisol concentrations were investigated on three days around estrus (day -1, day 0 = estrus, day 1) and in diestrus (day 7, day 8, day 9) each. Aggressive behavior significantly increased on day 0 (estrus) and the guinea pigs spent less time in the shelters and more time feeding on day 9 compared to day 7 in diestrus. Cortisol concentrations were increased around the time of estrus versus diestrus and body mass was decreased on day 0. None of the behavioral parameters affected cortisol concentrations considerably, except for a weak negative effect of the time spent feeding. This study demonstrates that the estrous cycle exerts an effect not only on physiological parameters but also on the behavior of group-living female guinea pigs. This represents an important starting point for future research and highlights stronger consideration of the estrous cycle when investigating (social) behavior and physiology in female guinea pigs.