The effect of venipuncture site on hematology of bats: implications for comparative analyses

Wildlife health comparisons within and across populations and species are
essential for population assessment and surveillance of emerging
infectious diseases. Due to low costs and high informational yield,
hematology is commonly used in the fields of ecoimmunology and disease
ecology, yet consistency and proper reporting of methods within these
fields are lacking. Previous investigations on various wildlife taxa have
revealed noteworthy impacts of the vein used for blood collection on
hematology measures. However, the impacts of venipuncture site on bats, a
taxon of increasing interest in ecoimmunology and disease
ecology,  have not yet been tested. Here, we use a long-term
study system in western Oklahoma to test the effect of venipuncture site
on hematology parameters of the Mexican free-tailed bat (Tadarida
brasiliensis) and cave myotis (Myotis velifer), two abundant and
representative bat species from the families Molossidae and
Vespertilionidae. Between September 2023 and October 2024, we collected
paired peripheral blood from both the propatagial and intrafemoral veins
in 25 individuals per species. We then quantified total red and white
blood cells, reticulocyte counts, and leukocyte differentials and used
generalized linear mixed models to compare parameters among venipuncture
sites within and between bat species. Overall, venipuncture site had no
effect on any hematology parameters; however, we revealed small
differences in neutrophil and lymphocyte proportions between veins among
the species. By contrast, we detected significant species-level
differences in most cell measurements, which we propose could be explained
by life-history strategy and phylogenetic differences. We encourage
continued testing of additional venipuncture sites, and of the same
venipuncture sites on different species, on hematology and other health
metrics used in ecoimmunology and disease ecology. Lastly, we emphasize
the importance of thorough method reporting in publications to enable
transparent comparisons and accounting for even small sampling-based
artifacts. All future efforts are especially important for bats to improve
conservation monitoring, ecosystem services estimations, and their
association with emerging infectious diseases.