Wednesday, September 3, 2008

Microflora in the Bird's Digestive Tract by Jeffrey Low

It is taimong season again. A couple of days ago, I was at a friend's place and noticed that his newly acquired wild taimongs are all given antibiotics in the drinking water. I think some keepers will give their newly acquired birds antibiotics as a precautionary measure. I do not know if this is a good thing to do. My thoughts are that antibiotics should only be given out of necessity to treat an infection and not given as a precautionary measure. One of the reasons for my thoughts being that the antibiotics will also wipe out all beneficial bacteria of the guts and this will affect the digestion and absorption of food.

Below is a write-up on the microflora of the bird's digestive tract based on my limited knowledge. It is nothing new but I hope it will create some awareness on this aspect of the bird's health for beginners to the hobby. You can search the net for more detailed information regarding the topic.


The microorganisms in the digestive tract of the bird perform various functions to benefit the host. They produce B-vitamins (biotin, cycobalamin), vitamin K and digestive enzymes. They also play an important role in the development and improvement of the intestinal wall structure for better food absorption. In return, they rely on the host for an ideal environment to thrive and for nutrients from the food that passes through the digestive tract. Hence a mutually beneficial relationship co-exists between these microorganisms and the host.

The microorganisms of the digestive tract are generally divided into two groups. One is beneficial to the host and the other is potentially pathogenic (disease causing). In the digestive tract of a healthy bird, a delicate balance exists between these two groups of bacteria. Maintaining this delicate balance is necessary for healthy digestive functions, which is imperative for optimal nutrient absorption and also for the general well being of the bird.

In a healthy bird, the beneficial bacteria predominate and occupy most of the available sites on the mucous membrane linings of the digestive tract. According to some sources, the optimal ratio of beneficial bacteria to pathogenic bacteria is 85:15

The beneficial bacteria thrive in an acidic environment while the pathogenic bacteria thrive in an environment with a higher pH. The beneficial bacteria, in particular the lactobacillus strains produce metabolic products such as lactic acid, which will lower the pH of the guts. This creates an unfriendly environment for the disease causing bacteria. In addition to this, the competition for nutrients and for space from the beneficial bacterial will also keep the pathogenic bacteria in check.

The beneficial bacteria also produce natural antibiotic-like substances (e.g. lactobacillus acidophilus produces acidophillin, lactolin and acidolin), which will act as a defense mechanism for the host against diseases and infections.

The delicate balance between the good and bad bacteria of a healthy digestive tract will be disrupted during times such as illness, stress, change of diet and antibiotic treatments. Under these circumstances, the beneficial bacteria can be significantly reduced causing a rise in the gut pH, creating a favourable condition for the pathogenic bacteria to flourish. When this happens, the damaging level of toxins produced by the thriving pathogenic bacteria will lead to illnesses for the host.

Probiotic supplements are cultured beneficial bacteria that are used to quickly re-establish the beneficial bacteria in the digestive tract when there is a disruption of the microflora. Newly acquired birds that are stressed from the change of environment, molting and breeding birds, birds that had undergone a course of antibiotics as well as birds undergoing a change of diet, will benefit from the use of probiotic supplements.

Prebiotics are non-digestible food to the bird that will stimulate the growth of beneficial bacteria in its digestive tract.

Most of the studies conducted so far on digestive tract microorganisms of birds are done on galliformes (poultry). There exists a theory that some species of birds under the order passeriformes have no resident bacteria in their bowels and do not rely on bacteria for their digestive functions. According to the 'Sterile Bowel Theory', these birds would require a much more improved digestion and absorption system to provide for the additional energy needed for their high metabolic rates. Hence, according to this theory, the oscine passerines (e.g. finches) that belong to the most advanced order of birds have evolved to develop a chemical digestion and absorption system, more efficient than the microbial system of other more primitive orders of birds. One of the facts used in support of this theory is that the oscine passerines have no caeca (the part of the digestive tract where bacteria is most concentrated to ferment and digest fibrous matter). It appears to me that there is still a lack of evidence to support this theory conclusively and more studies will be needed to prove that this is the case.

On the other hand, the hummingbird (apodiformes) has among the highest metabolic rate of any vertebrate and also has no caeca. It has been found that they still rely on the presence of a large population of bacteria found in their intestinal tracts. Flower nectars, which form the main diet of this bird, contain low level of amino acids. It has been shown in the hummingbird that nitrogen recycling takes place through the degradation of ammonia, urea and uric acid by the intestinal bacteria, to compensate for this low dietary nitrogen.

Links to some studies:

Upregulation of Oxidatiive Burst and Degranulation in Chicken Heterophils Stimulated with Probiotic Bacteria:

Improvement of Laying Hen Performance By Dietary Prebiotic Chicory:

Intestinal Mucosa Development in Broiler Chicken Fed Natural Growth Promoters:

Decomposition of Nitrogenous Compounds by Intestinal Bacteria in Hummingbird: ... AUK120.pdf