Establishment of the Microflora and Anaerobic Fungi in the Rumen of Lambs

SUMMARY: The establishment of different bacterial populations and fungi in the rumen was investigated in lambs reared under different conditions of diet and management. The rumen was rapidly colonized by an abundant microflora after birth. By day 2 strictly anaerobic bacteria predominated (109c.f.u. ml−1); their population increased slightly during the first week of life and again when the animals began to ingest solid feed (3 weeks). The composition of the microflora in the 2-10-d-old lambs was quite different from that of adult sheep. The aerobic and facultatively anaerobic bacterial count was 10-100-fold lower than the strictly anaerobic count during the first week, and decreased steadily afterwards. In flock-reared lambs, cellulolytic and methanogenic bacteria appeared very early after birth (3-4 d). At the end of the first week the population of these bacteria reached a level close to that generally observed in a mature rumen. The cellulolytic bacteria were also able to survive in the rumen of lambs fed cow's milk exclusively. Anaerobic fungi appeared later (8-10 d). They were present in all lambs studied until 3 weeks of age, and then disappeared in most of them when a solid diet was given.