In Caged & Aviary Birds
By Dr Colin Walker BSc, BVSc, MRCVS, MACVSc
The bacteria-host relationship
Through evolution, bacteria and warm-blooded animals have closely
associated themselves to form a closed system for mutual benefit.
By trial and error, over millennia, populations of bacteria have
evolved that are indigenous to their animal host. The animal host
receives the benefits of aid in the digestive process, manufacture
of essential nutrients, protection against other undesirable bacteria,
assistance in control of water in the body and other metabolic advantages.
The bacteria in return receive temperatures favourable for their
growth, a constant supply of nutrients, and essential substances
in the form of the body’s secretions. Because of the exact
nature of this relationship, there are bacterial populations that
are the most favourable for the host animal.
Each member of this mutually beneficial relationship is profoundly
influenced by the other. When certain changes occur in the host,
corresponding changes are reflected in bacterial populations
in the bowel. Bacterial changes may occur as a result of stress,
diet change, antibiotic therapy and other factors. Conversely,
as the resident bacterial population changes, there are subsequent
changes in the animal’s activity. These include alterations
in the host’s ability to digest its food and its ability
to protect itself from bowel disease. The animal host then has
the problem of getting back to an ideal relationship with its
normal resident population of bacteria. Hopefully it can accomplish
such a relationship before subsequent challenges again upset
the ideal state.
Where animals are not stressed, have an appropriate diet, are
not crowded, are not given drugs, do not contract infection or
metabolic diseases and live in a clean environment, an ideal level
of intestinal bacterial population may be maintained on a rather
steady basis. In fact, no differences are generally reported in
numerous trials under these ideal conditions.
The conditions described above, however, do not fit the environment
under which many birds are kept. Even in the best aviaries, under
the best care, birds are subjected to various stresses. This
means that disruption of the normal balance of intestinal bacteria
can be a common event. If an ideal state is not maintained, utilization
of nutrients is not optimal and resistance to harmful organisms
What is a probiotic?
The bacteria that are normally found in the bowel of healthy non-stressed
animals can be cultured and prepared as a medication. In this
form they are called probiotics. The probiotic concept involves
the refeeding or reintroduction of these bacteria to an animal.
Many studies in many countries have shown that, although these
bacteria can control and exclude other harmful bacteria, they
are in fact the most likely to be disrupted by stress. Most probiotic
products consist of naturally occurring living cultures of specific
strains of Lactobacilli and enteric Streptococcus (Enterococcus).
Restoring the balance
Once it was established that the feeding of certain live bacteria
to animals has the potential to produce beneficial effects under
certain circumstances, i.e. when the normal bacterial balance has
been disrupted, the actual delivery of these organisms from the
laboratory to the animal became the next hurdle. Pharmaceutical
companies have now overcome this. The large Japanese pharmaceutical
company Yakult manufactures a human probiotic (Lactobacillus casei)
as a milk-based drink in Victoria. This is distributed through
the eastern States of Australia. One million bottles are consumed
by Australians every week. Fourteen million are consumed in Japan
every day! Interestingly, in people, studies have shown that individuals
who drink ‘Yakult’ and are exposed to diseases such
as Salmonella are much less likely to become unwell. Probiotic
use in people has also been shown to decrease the chance of bowel
cancer. As many of the harmful bacteria produce toxins that are
carcinogenic, i.e. can induce cancer, their exclusion can decrease
the risk of this disease.
In birds, there are gel preparations of probiotics for individual
dosing and also water-soluble powders to treat the flock. These
provide selected beneficial live bacteria with excellent stability
when protected from extreme heat and moisture. Because of the intimate
relationship between the host animal and its bacterial population,
it is important that the correct organisms are supplied in probiotic
preparation for any given species. Probiotic supplements need to
be prepared with particular species in mind and the more types
of normal bacteria that can be provided, the better. For use in
birds, therefore, multistrain avian-origin probiotic supplements
At the seventh European Association of Avian Veterinarians conference
held in April 2003 at Loro Parque in Tenerife, an interesting
paper was presented on probiotic use in cockatiel chicks. This
paper described work done at Louisiana State University by a
team headed by Dr. Tom Tully. Cockatiel chicks were removed from
their parents at 12 days of age and hand rearing commenced. They
were divided into several groups, some of which received probiotic
supplementation, and some of which did not. During the hand raising,
weight gain and the ability to resist disease were monitored.
Results showed that there was no difference in weight gain in
healthy chicks on a good diet. The team went on to state “Although
not significant in benefiting healthy babies being fed an adequate
diet, in all likelihood babies being fed marginal diets by inexperienced
feeders, stressed and or diseased birds should benefit from an
avian specific probiotic supplement fed on a daily basis”.
During hand raising the birds were deliberately infected with
disease-causing bacteria (Pseudomonas sp, E. coli). Testing of
the birds after infection with these bacteria showed that the probiotic-supplemented
group was less likely to be pathogen positive. Subsequent blood
tests showed less of an inflammatory response (lower white blood
cell count) and subsequent histopathology showed less infection
in the intestines.
At the AU convention in October 2003 in Chicago research work
was presented by Star Labs. Star Labs are based in Missouri and
manufacture a probiotic preparation called “PrimaLac”.
Two large trials had been conducted with this product. In one trial
involving over 20,000 Bob White quail chicks it was shown that
probiotic-supplemented birds, when compared to non-probiotic-supplemented
birds, had improved growth, improved feed conversion, and improved
feather quality, and were more likely to survive. They also exhibited
an enhanced immune (antibody) response. The second trial involved
approximately 15,000 pheasants. These birds were also divided into
probiotic-supplemented and non-supplemented groups. Both groups
were then deliberately infected with Salmonella typhimurium (a
disease causing bacteria) and then later Newcastle disease (caused
by a paramyxo virus). In both instances approximately 25% more
of the non-probiotic-supplemented birds died.
Mode of action
And so how do probiotics work?
Competitive inhibition – The normal bacteria found in the
bowel of some birds during health, e.g. Lactobacillus sp., produce
lactic acid, hydrogen peroxide, antibiotic and other substances
that help keep potential pathogens under control. In health the
lactic acid produced by the normal bacteria keeps the PH of the
contents of the stomach and intestine low i.e. acidic. Loss of
these normal bacteria, secondary to stress, leads to an increase
in PH. As a general rule, most pathogenic bacteria do not multiply
well in an acidic environment and so a rise in PH creates a window
of opportunity for disease causing bacteria to invade. As many
aviculturalists are aware, likely potential invaders include E.
coli, Pseudomonas, Candida (yeast or thrush), Salmonella and Yersinia.
Often these organisms act as opportunists, waiting to cause disease
whenever birds become stressed. In addition to weakly acidifying
the bowel, probiotics do much more to help the bird, in that they
produce protective slime layers that coat the bowel lining and
also preferentially occupy receptor sites on the bowel wall, in
the process excluding bacteria such as E. coli. They can offer
an effective natural way of combating the problem without the need
for antibiotics. By treating the birds, we are simply flooding
the bowel with beneficial bacteria, which, through their normal
activity may re-establish health.
Appetite stimulation - Probiotics appear to have a strong appetite-stimulatory
effect. They are known to produce digestive enzymes and B vitamins.
These effects help the birds to get the maximum nutrition from
Immune stimulation – Recent work indicates that probiotics
stimulate general immunity.
Interestingly, it appears human probiotic preparations are being
developed to target specific bacterial infections. In humans, a
bacterium Bacillus cereus causes gastroenteritis. This infection
is not fatal but is responsible for many lost days of work annually
in the population. Rather than being prescribed antibiotics, in
the future patients may be prescribed a specific probiotic ‘yoghurt’ that
controls the infection. According to the companies involved, with
this technology now in place, more difficult organisms like E.
coli, which have a large number of strains and mutate more readily,
will be tackled. Once available, these preparations will be beneficial
and useful to aviculturalists as they will mean that such infections
can be managed without resorting to antibiotics with their associated
risk of side effects.
Use of probiotics
Although probiotic preparations have been available for several
years, there still seems to be some uncertainty about their use.
As always when new products become available, it is easy for
misinformation to be spread. The situation is complicated by
the fact that not all birds have the same or even similar populations
of bowel bacteria. Birds with caeca, such as chickens, carry
large numbers of what are called gram-negative bacteria, which
are capable of causing disease in other species. In birds such
as parrots with no caeca, the number of gram-negative bacteria
is very low, but large numbers of gram-positive bacteria are
normal. In lorikeets, virtually no bacteria are found, while
in many passerines such as canaries and Australian finches, no
permanent population of bowel bacteria exists, with the bacteria
found in droppings being regarded as transients.
Although not a miracle cure, it does seem that probiotics can
be beneficial in certain situations to help maintain the health
of our birds.
So when can the aviculturist use probiotics to his advantage?
After any stress - Stress predictably disrupts the population
of bacteria found in the bowel with the beneficial bacteria being
the first ones to be lost. Once these beneficial bacteria are removed,
an opening is created for an overgrowth of disease causing bacteria
or yeasts. This can result in diarrhoea, decreased appetite and
a vulnerability to disease. Probiotics restore the balance of beneficial
to non-beneficial bacteria. They are best given as soon as possible
after the stress or just before the time of the stress. By doing
so, disease problems may be avoided.
During breeding and moulting – Often, despite the best of
care, breeding or moulting birds can become “run down”.
Probiotic use is likely to protect the parents and, during breeding,
the babies from disease.
Following purchase and transport – Catching and confinement
can be extremely stressful particularly in naturally nervous species.
Interrupted feeding and drinking patterns provide further physiological
Following antibiotic use – Many antibiotics not only target
disease-causing bacteria, but also kill the beneficial bacteria
of the bowel. When antibiotic treatment ceases, the bowel can re-populate
with bacteria from the birds’ immediate environment. Probiotics
can help protect the birds from disease during this time.
After fledging – Less disease can be expected after weaning
if birds are probiotic-supplemented until they are feeding properly
and have established themselves in the aviary.
Note on Probiotic Use
In some metropolitan areas, the addition of fluoride or chlorine
to drinking water may interfere with the action of probiotics.
In metropolitan areas, treatment plants are situated throughout
the water-distribution network. According to Australian authorities,
the concentration of fluoride and chlorine throughout most of
the network is too low to exert an effect. However, the concentration
in the water of aviculturalists close to a treatment plant may
be high enough to kill the probiotic organisms. These substances
will, however, evaporate from treated water if it is allowed
to stand for 24 hours. Aviculturalists in any doubt are best
to set aside water to be medicated with probiotics for 24 hours
before use. Simply standing the required volume of water in several
buckets awaiting use is adequate. Alternatively, rainwater or
distilled water could be used. Most water-soluble probiotic preparations
can be added to the feed. Indeed, with some preparations, this
ensures a more immediate and effective delivery of the probiotics
to the digestive tract.