A new method to measure the redox potential (Eh) in rabbit caecum: relationship with pH and fermentation pattern

[EN] This study aimed to assess the anaerobic status of the caecal biotope in the rabbit through the measurement of its redox potential (Eh). Since the caecal content has a high viscosity, the duration of the Eh measurement is high (10 to 20 min) and two methods were compared in 10 week- old rabbits: in vivo vs. post-mortem. In addition, Eh, pH and temperature of the caecal digesta were analysed according to caecotrophy and three periods in the day (soft faeces production: 08:00-10:00 h and 12:00-14:00 h; hard faeces production: 17:00-19:00 h) were compared, using 34 rabbits aged 65 d and weighing 2.3 kg. Caecal Eh decreased 2 min after measurement began, and then stabilised from 20 min onwards (from -152 to 221 mV, P<0.001), in contrast to caecal pH which remained constant over time. Mean values for Eh (at 20 min) and pH were - 219 mV and 6.2 respectively, and did not change according to method or collection period. Only the caecal temperature was 2°C higher (P<0.001) for the in vivo (39°C) than for the post-mortem (37°C) method. Average caecal dry matter and total volatile fatty acid were on average 22 % and 106 mmol/L, and were affected neither by the method nor by the collection period. Caecal Eh was negatively correlated to caecal pH (R²=0.22; P=0.006, n=34), but not to other biotope traits. The Eh measurement in rabbit caecal content could be performed with a minimum recommended duration of 20 min, under anaesthesia or post-mortem. We confi rmed that the rabbit caecal ecosystem is highly anaerobic.