Changes in maternal fecal corticosterone metabolites across lactation and in response to chronic stress

•Chronic stress increases fecal corticosterone metabolites (FCMs) in lactating rats.•FCMs did not change across lactation in control rats.•FCMs in chronically-stressed rats increased in late lactation.•This change may be due to lactation stage and/or repeated exposure to the stressor.•This study highlights the need for repeated temporal sampling across lactation. Maternal exposure to stressors during lactation has previously been demonstrated to impact various aspects of milk synthesis and to have long-term physiological effects on offspring. Much of the current literature investigating the effects of stress during lactation has used acute stressors, and the studies investigating the effects of chronic stressors largely focus on neurological changes. Further, temporal variation in glucocorticoids across lactation in response to stressors has rarely been assessed. The present work uses a novel male intruder paradigm to model the effects of chronic stress on maternal fecal corticosterone metabolites (FCMs) in Sprague-Dawley rats across lactation. FCM levels were elevated in chronically-stressed mothers relative to the control group. Further, FCMs in the stress group were time-dependent either due to repeated exposure to the stressor or lactation stage. Together, this work demonstrates the efficacy of this established paradigm in increasing circulating glucocorticoids in lactating rats. These results highlight the need for repeated temporal sampling, as glucocorticoid levels in response to a chronic stressor may change across lactation.