Development of an ethogram to investigate cattle odor exploration behavior of Swedish dairy heifers.

Olfaction is a key sensory modality in cattle, yet the behavioral repertoire associated with odor exploration remains insufficiently described. Existing studies have primarily focused on sniffing, with limited characterization of additional behaviors that may contribute to olfactory assessment. This study aimed to describe the full range of odor exploration behaviors expressed by dairy heifers and to develop an ethogram specifically adapted for this context. The study was conducted with 21 dairy heifers, each exposed to 10 essential-oil odors in 5-min one-exposure tests performed within their home environment. This resulted in 207 analyzable tests after 3 were excluded due to disturbances during the tests. Video footage was used to identify all behaviors expressed during odor exploration. An initial ethogram based on previous literature was expanded through iterative coding of 40 tests. Behaviors were categorized as odor exploration or other (not odor) exploration using a predefined sniffing criterion. A randomized subsample was used to evaluate intra-observer reliability, and the refined ethogram was applied to the full data set to characterize behavioral distributions. The ethogram comprised a structured and comprehensive set of odor-directed and other exploratory behaviors, including sniffing, scratching, licking or biting, head shaking, head butting, mouth opening, tongue movements, vigilance, kicking, elimination as well as ear and tail postures. Intra- and inter-observer reliability showed moderate to excellent agreement, indicating that the behavioral definitions were sufficiently clear and operational to be applied consistently. This supports the usefulness of the ethogram for future research and its potential to be adapted to other study designs. This study provides a systematically developed and empirically evaluated ethogram describing the behavioral repertoire of dairy heifers during odor exploration. The ethogram expands the methodological tools available for cattle olfaction research and offers a standardized framework for future studies on sensory processing and odor-driven exploratory behavior.