The aim of the present study was to provide information on the causes of mortality among the chickens of the DLS poultry farm, starting from day old through the laying period and quantification of losses attributed to avian colibacillosis.
Two different studies were performed: An observational study on the morality at three different parent stock flocks of different ages of Mirpur Government Central Poultry Farm, Bangladesh . 83% of the dead animals were subjected to necropsy. Diagnoses were based on clinical signs, gross lesions and bacteriological examinations, when indicated. In a study of experimental colibacillosis, the infection was reproduced with a field isolate of Escherichia coli O139 as a monoinfection and also along with infectious bursal disease (IBD), using a field virus isolate. This was done in unvaccinated birds as well as in birds vaccinated against IBD. The economic analysis was based on the calculation of stock losses due to mortality and effect and influence of the IBD vaccine on mortality and feed conversion efficiency of the birds.
In the observational study significantly higher mortality was observed in the youngest flock. In this group the predominant causes of mortality were IBD (10%), colibacillosis (3%), salmonellosis (3%), aflatoxicosis (1%) and coccidiosis (0.9%). In the adult groups the predominant causes of mortality were: salmonellosis (2 %), colibacillosis (1%), egg bound (0.4%), cannibalism (0.1%). In the young birds the cumulative incidence and incidence rate of colibacillosis were higher than those of salmonellosis, whereas the opposite was true for the adult birds.
From the present as well as previous studies it appears that in spite of IBD vaccination there was an outbreak of IBD. The presence of aflatoxin is a possible cause of vaccination failure, as aflatoxicosis was demonstrated in the flock of young birds, and aflatoxin is known as an immunosuppressing agent.
In the experimental study significantly higher morbidity and mortality were observed in the unvaccinated, double-infected group than in the unvaccinated, only E. coli infected group as well as the vaccinated, only IBD infected group. Before challenge, the average feed conversion ratio (FCR) was significantly higher in the vaccinated groups and remained significantly higher in those vaccinated groups, which were challenged with E. coli alone or along with IBD virus. This is probably is due to stress following the use of the live IBD vaccine and further exacerbation of the condition of the birds due to experimental infection with E. coli.
From these results it can be concluded that morbidity and mortality are significantly higher in dual infections. Moreover application of live IBD vaccine impairs the efficiency of feed conversion. This is further aggravated by E. coli infection.
According to the economic analysis of the observational study, the annual loss of revenue was Tk 428372, which is equivalent to $7196 due to the death of 1821 birds in three different flocks and according to present experimental study the application of vaccine could save a maximum amount of $186/1000 layers/laying year. However, the vaccine reduces the efficiency of the birds, resulting in an increase of feed conversion ratio, which indicates that to produce the same amount of meat the vaccinated birds need 58% more feed, equalling an amount calculated to be $ 177/1000 birds/35 days.
According to the findings of the present observational study, the disease situation in the parent flocks investigated is rather unsatisfactory, not only due to high flock mortality but also because of the possibility of transmitting some diseases, such as colibacillosis and salmonellosis, to the field level through their offspring. Important measures to improve the situation are the establishment and maintenance of specific pathogen free grand parent stock flocks and improvement of biosecurity of the rearing sheds for the parent flocks, the hatcheries and the distribution chain. This would save expenses equalling $7196/10334 birds/4 months and additionally would ensure the distribution of healthy birds for the field level. Vaccination against IBD could be recommended for layers providing the supply of fresh feed, good hygienic and otherwise unstressed conditions for the birds, however, further study is needed for evaluation of the relevance for meat producing birds.
Future information is needed on prevailing predisposing factors of colibacillosis, including concurrent infections, degree of virulence of prevailing E. coli, presence of mycotoxin in the feed, managemental issues, such as hygienic measures related to rearing shed / hatchery / distribution chain, etc. Moreover, more information on health status in the filed level is needed. Influence of indiscriminate use of antibiotics on bacterial infections of the birds should be investigated due to the consequences for the resistance situation, and residual concentrations in the products. |
