Alternative methodologies to estimate ingestion of caecotrophes in growing rabbits

This study was carried out in order to estimate caecotrophe intake in growing rabbits by three existing procedures: caecotrophes collection after collar fitting, urinary purine derivatives (PD) excretion and microbial 15N-lysine incorporation. In a first experiment sixteen New Zealand White male rabbits were divided in three groups receiving the same diet, but supplemented with 15NH4Cl in the first group (T1: 6 rabbits). The second group (T2: 6 rabbits) was also fed the labelled diet but only during the last ten days of the fattening period when animals were fitted a neck collar to prevent caecotrophy. The third group (T3: 4 animals) received the basal diet and was used as control. In two additional trials the daily contribution to urinary excretion of endogenous purine compounds (469 ± 50.8 μmol/W0.75) and creatinine excretion (807 ± 127.6 μmol/W0.75) were determined. The highest estimation of microbial nitrogen recycling was obtained by the urinary PD method (0.79 ± 0.096 g/d), whereas caecotrophes collection and 15N-lysine incorporation methods showed similar values (0.49 ± 0.049 and 0.45 ± 0.015 g/d, respectively). Our results seem to indicate an overestimation of microbial nitrogen recycling in growing rabbits by PD methodology, while neck collar fitting procedure gave similar results, although more variable than microbial 15N-lysine incorporation.