Application of the iButton® for measurement of the rumen temperature circadian rhythms in lambs

The aim of this study was to investigate the daily rhythm of rumen temperature (Trumen) in lambs by means of the iButton®. Temperature data loggers were orally implanted in five, clinically healthy, male Comisana lambs (150 ± 5 days old; 31.5 ± 1 kg) under natural environmental conditions in order to record the daily course of Trumen. After six days of implantation, animals were slaughtered and iButtons® were recovered from the rumen. One-way repeated-measures analysis of variance (ANOVA), applied to evaluate the effect of time of day on Trumen, showed significant differences (p < 0.0001) in all days of monitoring. The application of the statistical analysis of cosinor indicated the existence of a significant daily rhythm (p < 0.001), with nocturnal acrophase (from 17.21 to 20.59 h). These findings provide new information on the relationship between circadian rhythms of rectal and rumen temperature, improving knowledge about their temporal organization in ovine species.