A biological validation procedure for the measurements of fecal outputs and fecal cortisol metabolites in male Syrian hamsters

Monitoring fecal outputs and fecal cortisol metabolites (FCM), a noninvasive technique, has been used to investigate physiological responses to stress and relationships between hormones and behavior in an increasing number of species. The aim of this study was to investigate whether measurements of fecal outputs and FCM can be used as indexes to repeatedly and precisely monitor stress levels in male Syrian hamsters using a social defeat as a biological validation method. The feces voided by each animal were collected every 3 h for at least 1 day before and after experiencing a single fighting interaction, and the extracted FCM during the pre- and post-fight phases was quantified by enzyme immunoassays. During the pre-fight baseline phase, both the number of fecal pellets and the FCM levels fluctuated throughout the whole day. Although the number of fecal pellets did not differ between the dark and light cycles, the levels of FCM were significantly higher during the dark cycle than during the light cycle. During the post-fight phase, the experience of fighting did not result in a significant difference in the number of fecal pellets per hour between the winner and loser groups, but did considerably increase the total amount of fecal outputs in both groups. The level of FCM was significantly higher in the loser group than in the winner group during the 1st and 7th 3-h collection periods after the fight, which indicated that the experience of defect affected the behavioral and physiological responses of the losers. Our findings suggest that measurement of FCM is sensitive enough to distinguish the stress levels between winners and losers after experiencing a fight. The measurements of fecal outputs and FCM levels provide new opportunities to longitudinally and frequently monitor behavioral and hormonal responses to stress in hamsters and other small laboratory animals.