In Caged & Aviary Birds
By Dr. Colin Walker BSc, BVSc, MRCVS, MACVSc (Avian health)
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 is reduced.
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 are used.
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 their diet.
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 stress.
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.