Development of the cellulolytic microflora in the rumen of lambs transferred into sterile isolators a few days after birth.

Seven lambs, separated from their dam 24 h after birth, were kept in a conventional environment until transferred to sterile isolators between 1 and 9 days of age: two on day 1 (IA and IB), two on day 4 (IVA and IVB), one on day 8 (VIIIA), and two on day 9 (IXA and IXB). The lambs were reared in these isolators until 120 days of age. Lambs IA, IB, IXA, and IXB were free of cellulolytic bacteria when they were placed in the isolators. They were then inoculated with Bacteroides succinogenes S85 which became established in the four lambs. Until the age of 2 months, the population of this strain fluctuated and then stabilized at a high level (10(8)-10(9) cells/mL). Cellulolytic bacteria were present in the rumen of lambs IVA, IVB, and VIIIA when they were transferred to the isolators. In IVA, and IVB, the cellulolytic population slowly increased with the animal age. In contrast, in VIIIA, the cellulolytic bacteria disappeared within a few days. Bacteroides succinogenes S85 inoculated thereafter became established rapidly and reached a level comparable to that observed in lambs IA and IB. The total number of viable rumen bacteria in the isolated lambs was similar to that observed in conventionally raised animals, but differences were observed in the selective enumeration of bacteria utilizing specific energy sources.