Evaluation of the quality of chicken carcasses used as feed for Nile crocodiles on commercial farms

Abstract

The average mortality rate on chicken farms in South Africa is ± 4.0% per annum. Commercial crocodile farmers have access to some of the ±750 000 chicken carcasses available per week (nearly 3 million carcasses per month). The feeding of chicken carcasses to crocodiles was investigated to identify the potential hazards. The hazards investigated in more depth, focussed on bacteria present in chicken carcasses during different stages of decomposition and the prevalence of antibiotic residues. Chicken carcasses used as crocodile feed, differ in states of decomposition - ranging from fresh to severely decomposed. Carcass “quality” has become a concern to commercial crocodile farmers, with many farmers questioning the value of these severely decomposed carcasses, with some stating that feeding of severely decomposed chicken carcasses to crocodiles makes them sick. Fifty-four chicken carcasses were left in an environmentally controlled poultry house. Carcasses were removed in 6-hour intervals after death; with the last group exposed to typical in-house environmental conditions for 36-hours. Carcasses were frozen immediately after collection (each group after removal from the house). When these carcasses were processed again afterwards, they were thawed and eviscerated for sampling of the gastrointestinal tracts (GITs) and rest of the carcasses, separately. The bacterial contamination of the GITs and rest of the carcasses was determined using standard laboratory methods. Salmonella spp., Listeria monocytogenes and Staphylococcus aureus were detected in 88%, 61% and 36% of the tissue samples, respectively. Samples testing positive for Salmonella spp. were serotyped and identified as Salmonella hamburg. Further results showed that mean log CFU/g for E. coli were significantly higher (P<0.05) in GIT (gastrointestinal tract) (5.433 log CFU/g) compared to MBF (muscle, bone and feathers) (4.783 log CFU/g). A difference of 1.9 log CFU/g between the same group suggest that mean log CFU/g increased over 12-hours for E. coli on carcasses. Carcass pH and temperature was measured and recorded after each 6-hour exposure period in each carcass, just before freezing, by making a 1 cm incision in the pectoral muscle and inserting a portable meat pH meter and temperature probe (HANNA HI 99163). The measurements recorded showed an average decrease in carcass temperature of 3.6⁰C between the 6-hour groups. The carcass pH decreased at a steadily rate of 0.15 units of pH/6-hours for the first three groups (12-hours exposed) and increased at a rate of 0.085 units of pH/6-hours for the last groups (36-hours exposed). Chicken carcasses used as crocodile feed vary in age and origin. Although withdrawal periods are adhered to in post-finisher poultry rations, chickens on grower and finisher rations take in pharmaceutical drugs that may pose a hazard to crocodiles and farmers exporting meat. Five commercial crocodile farms were used for collecting samples from minced chicken carcasses - prepared as crocodile feed on the farms. Three separate samples (± 20 gr each) were collected from chicken carcasses from each crocodile farm. Totalling 15 samples that were screened for 15 antibiotic compounds using the LCMS/MS technique (liquid chromatography / mass spectrometry). All samples submitted tested negative (< 50 μg/kg). This result concludes that poultry carcasses do not pose as a hazard for antibiotic residues when used as feed for commercial crocodiles. Distinct carcass observations in the decomposition trial were used to determine if they could be used in developing a practical carcass evaluation method. Skin colour and carcass deterioration were chosen and used in the evaluation. Carcasses were easily identified by skin colour (red, green and blue). “Blue” carcasses confirmed deterioration and “red” did not when subjected to the pull-test, a technique developed in this project and used to determine carcass deterioration by pulling the legs apart, confirming deterioration, or resisting the pull test and remaining intact. The carcass evaluation method was performed on the commercial crocodile farms taking part in the questionnaire and on-farm hazard identification. A questionnaire was discussed with farmers and managers from 5 crocodile farms to gather information and compare the different methods of chicken carcass evaluation, preparation and feeding. The information gathered from the questionnaire and hazard identification confirmed that severely decomposed carcasses pose as a possible hazard if included as feed for hatchling and grower rations. These carcasses have the posibilty of increasing or introducing antibiotic resistant bacteria in feed, thus increasing the risk of disease outbreak. A management plan for feeding chicken carcasses to crocodiles was developed for commercial crocodile farmers addressing the source, transport, processing and storage of carcasses. In conclusion, results from the first two sub-projects (first 2 sub-projects as discussed above), together with our on-farm questionnaire and investigation, were used to evaluate the potential hazards associated with using chicken carcasses as feed for crocodiles. In our opinion, the risks to crocodiles, on commercial crocodile farms consuming chicken carcasses, are relatively low. Especially, if farm managers are willing to apply the proposed management plan discussed in this thesis, as well as general biosecurity guidelines.