In vitro study of the age-dependent caecal fermentation pattern and methanogenesis in young rabbits

― The caecal fermentation pattern, including methanogenesis, was studied in young rab- bits using in vitro batch incubations. Six conventional litters of eight rabbits each were used. At the age of 22, 25, 28, 32, 36, 42 and 56 days, an animal was slaughtered from each litter and its caecal con- tents were used for in vitro batch incubations at 39 C/24 h. The incubated samples were analysed for volatile fatty acids (VFA), methane, hydrogen, ammonia nitrogen (NH 3 -N) and lactic acid (LA). The net total in vitro VFA production did not differ clearly with age, although a significant decrease was observed on day 36, reflecting the reduced zootechnical performances probably related to an infection with Clostridium spiroforme that occurred in the same period. The molar proportions of butyrate and propionate formed a change in the opposite direction with age, starting with a sudden shift from propionate to butyrate at day 25. In vitro NH 3 -N production was suggestive of a progressive and significant decrease with age; in vitro LA production was always low. Methane production was almost absent from fer- mentation until 32 days of age, after which it suddenly shifted from 1.6 to 52.0 N mol/flask/day and increased further with age. A significant litter effect on methanogenesis was observed which suggested the existence of a genetic effect. The hydrogen production was quite low and decreased significantly from day 36 with increasing methanogenesis. The calculated hydrogen recoveries showed a gradual increase from day 32 and were positively correlated (r= 0.92) with methane production. In conclusion, it would seem that in young suckling rabbits, reductive acetogenesis is a major characteristic of caecal fermentation, to be replaced gradually and partially by methanogenesis with the increasing intake of solid feed. rabbit / caecum / in vitro VFA / methane Rsum ― tude in vitro de l'effet de l'ge sur l'activit fermentaire caecale et la mthanogense chez le lapereau. L'activit fermentaire caecale et particulirement la mthanogense ont t tu- dies chez les lapereaux l'aide d'incubations in vitro. Six niches de huit lapereaux chacune ont t utilises. l'ge de 22, 25, 28, 32, 36, 42 et 56 jours un lapereau de chaque niche a t sacrifi et le contenu cxcal chantillonn pour tre incub dans un bain-marie 39 C. Aprs un priode d'incubation de 24 heures, la production d'acides gras volatils (AGV), de mthane, d hydrogne, de lac- tate (L) et d'azote ammoniacal (NH 3 N) a t dtermine. La production nette des AGV totaux ne varie pas clairement avec l'ge ; on observe une chute significative 36 jours d'age refltant une diminution des performances zootechniques observe entre le 32 e et le 36 e jour, probablement due une infection parClostridium spiroforme, survenue cette priode. Les proportions molaires du propionate et du butyrate voluent en sens inverse avec l'ge de telle faon qu'au 25 e jour on observe une diminution soudaine du propionate au profit du butyrate. La production,in vitro de N-NH 3 diminue pro- gressivement et significativement avec l'ge, alors que celle du lactate reste basse. Il n'y a pas de pro- duction de mthane jusqu au 32 e jour. Au-del de cette priode la production de ce gaz est passe brus- quement de 1,6 52,0 0 pmoles4lacon4our et a continu augmenter par la suite. Quant la production de mthane, la variabilit entre les niches suggre un effet gntique sur ce paramtre. La produc- tion d'hydrogne est faible et diminue avec lge et avec l'augmentation de la mthanogense. Le bilan d'hydrogne est positivement corrl avec lge (r = 0,92) et la production de mthane. En conclusion, il semble que l'actogense rductrice est la principale caractristique fermentaire dans le caecum de jeunes lapins. Cette voie serait progressivement et partiellement remplace par la mtha- nogense lors de l'ingestion des aliments solides. lapin / caecum lAGV in vitro lmthane