Manure odor profiling for flock-level monitoring on commercial layer pullet farms: Vaccination events as a model stressor

Continuous, non-invasive, and objective methods to detect flock-level responses to stressors, including intestinal health deviations, are currently lacking in poultry. This proof of principle study investigated the potential of manure odor profiling in monitoring stress responses in Lohmann Brown Classic, Lohmann LSL Classic and Lohmann LSL Lite layer pullets. Stressors were represented by a Salmonella vaccination given to the pullets at wk 3 of age (Dataset 1 and Dataset 2) and wk 16 of age (Dataset 4) and a viral/bacterial vaccine cocktail given at wk 12 of age (Dataset 3). Fresh manure was sampled daily, from 2 days before vaccination to 4 days after vaccination, with 4 pooled manure samples per day per dataset. Manure volatiles were concentrated into stainless steel sorbent tubes and analyzed by a thermal desorption system coupled with gas chromatography-mass spectrometry. Dataset, breed and sample location did not affect the manure volatile profiles before vaccination. Age did affect the manure volatile profiles, with beta-camphor, (Z)-6-Tridecene and serinol peak intensities elevated in young pullets and carbonyl sulfide and trimethylamine elevated in older pullets. Salmonella vaccination at wk 3 of age led to the most consistent changes in volatile peak intensities. (Z)-6-Tridecene was decreased in Dataset 1, Dataset 3, and Dataset 4 after either the Salmonella vaccination or the viral/bacterial vaccine cocktail, despite differences in hen age and house. The injected viral/bacterial vaccine cocktail created a more clear time-dependent shift in the manure volatile profile than the orally-provided Salmonella vaccination in older pullets at resp. wk 12 and 16 of age. No overlapping trends in upregulated or downregulated volatiles were found between all datasets. To conclude, volatile profiles of rearing hen manure are affected by vaccinations as a proxy for stressors, and the magnitude and direction of the response depends on the age of the pullets at vaccination, the vaccination method, and the pathogenic properties of the vaccine. The reduced peak intensities of volatiles after vaccination in 3 out of 4 flocks suggests the potential of manure odor profiling in monitoring stress responses in layer pullets.