The intestinal flora of the chicken in the period 2 to 6 weeks of age, with particular reference to the anaerobic bacteria

A study has been made of the intestinal flora of chickens aged between 2 and 6½ weeks. No major differences were found when rations containing 9 or 25% fish meal were compared or when two different sources of fish meal were used. Throughout the period investigated, it was confirmed that the lactobacilli are the only group of organisms generally present in the small intestine in numbers exceeding 104/g. Clostridia were regularly found at 102 to 104/g, but Clostridium welchii was isolated from only occasional samples.

In the caeca, the total number of bacteria present at 2, 3, 4 and 6½ weeks was about 1011/g. Of these it was generally possible to isolate more than 20% using an anaerobic roll‐tube technique and oxygen‐free CO2. Many different types of anaerobes were isolated including strictly anaerobic budding bacteria which had not previously been studied. During the growth of the bird the flora changed. Anaerobic streptococci (peptostreptococci) predominated at 2 weeks but gradually decreased so that by 6½ weeks these organisms formed only a small part of the flora. Many of the Gram‐negative non‐sporing anaerobes only appeared between the 4th and 6th weeks.

Throughout the 2 to 6½‐week period all the caecal samples examined contained 108 to 109 anaerobes/g which were able to attack uric acid and sometimes 1010/g. This property was shared by at least one group of peptostreptococci, four groups of Gram‐negative non‐sporing anaerobes, three groups of Gram‐variable or Gram‐positive anaerobic non‐sporing rods and several species of clostridia.