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

Abstract

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.