2013 Annual Report
For all sampling intervals and all sample types combined across the life of flock 1, the mean number of total aerobic bacteria that were detected in environmental samples taken from aviaries (5.1 log cfu per ml of initial sample diluent) was significantly (P < 0.0001) higher than from either enriched cages (4.5 log cfu/ml) or conventional cages (4.1 log cfu/ml). However, no corresponding differences between housing systems were identified for counts of Enterobacteriaceae (1.2 log cfu/ml for enriched cages, 1.2 log cfu/ml for aviaries, and 1.1 log cfu/ml for conventional cages).
The general trends in the mean numbers of bacteria detected in environmental samples were similar for both total aerobes and Enterobacteriaceae. Moreover, some similarities in the bacterial counts associated with the various sample types were observed between the three housing systems. In all three housing systems, the highest numbers of both total aerobes and Enterobacteriaceae were recovered from manure belt samples. In both aviaries and conventional cages, the counts of both aerobes and Enterobacteriaceae from manure belts were significantly (P < 0.0001) higher than from any other type of sample. In aviaries, nest boxes also yielded relatively high counts of both types of bacteria, whereas egg belts provided consistently low bacterial counts. In enriched cages, egg belts, egg elevators, and egg ramps were good sources of bacteria, but low counts were found in association with cage floor and roost samples. In conventional cages, egg belt samples provided high bacterial counts but cage floor samples provided low counts.
Efforts to enumerate Enterobacteriaceae from egg shells revealed consistently very low numbers of bacteria (<0.2 log cfu/ml of sample rinsate), with no significant differences found between housing systems. On the other hand, enumeration of total aerobic bacteria on egg shells indicated significantly (P < 0.0001) higher numbers on aviary floor eggs (3.9 log cfu/ml) than on eggs from conventional cages (2.8 log cfu/ml). Intermediate total aerobe values were obtained for eggs from nest box collection areas of aviaries (3.3 log cfu/ml) and enriched cages (3.02 log cfu/ml).
A significant (P < 0.0001) interaction was observed between the three housing systems and Salmonella isolation. Overall, Salmonella was isolated from 222/400 samples (55.5%) from conventional cages, 93/576 samples (16.2%) from aviaries, and 14/560 samples (2.5%) from enriched cages. However, the frequency of Campylobacter isolation from environmental samples was not determined to be significantly influenced by the three housing systems. Because of significant variation between results obtained on different sampling dates, apparent numerical differences between housing systems did not prove to be statistically significant. Overall, Campylobacter was isolated from 112/504 samples (22.2%) from aviaries, 52/494 samples (10.6%) from enriched cages, and only 23/350 samples (6.6%) from conventional cages.
In aviaries, Campylobacter was recovered at the highest frequency from cage floor samples (45.2%), followed by manure belt and roost samples (each 34.5%). In enriched cages, the highest frequency of Campylobacter recovery came from nest area samples (24.3%), followed by manure belts (22.9%). In conventional cages, cage floors yielded the highest frequency of recovery (17.1%), followed by manure belts (15.7%). In addition, 5 of 294 sampled egg shells (1.7%) were positive for Campylobacter (3 of these 5 came from aviaries).
Salmonella was recovered in aviaries at the highest frequency from manure belt samples (52.1%), followed by nest box samples (14.6%). In enriched cages, Salmonella was most often recovered from egg belts (6.3%), followed by egg ramps and manure belts (each 3.8%). The highest frequency of Salmonella recovery from conventional cages was obtained from manure belts (81.3% positive), followed by egg belts (70.0%). Salmonella was also found on 9 of 336 sampled egg shells (2.7%), all from conventional cages.
A total of 283 environmental Salmonella isolates were serotyped by intergenic sequence ribotyping (Table 3). Overall, 62.2% of these isolates were S. Braenderup, 30.4% were S. Kentucky, 6.7% were S. Mbandaka, 0.7% were S. Infantis, 0.4% were S. Agona, and 0.4% were S. Anatum. Among 190 isolates from conventional cage housing, 83.3% were S. Braenderup, 9.5% were S. Mbandaka, and 6.3% were S. Kentucky. Among 85 isolates from aviaries, 80% were S. Kentucky and 16.5% were S. Braenderup. Among 8 isolates from enriched colony housing, 62.5% were S. Kentucky and 37.5% were S. Braenderup.
The second flock of laying hens for the study is currently under production. Microbial assessments for the second flock have changed from the first flock to account for the direction of the new research team.