Technical note: preorbital gland opening in red deer (Cervus elaphus) calves as an indicator of stress

The opening of the preorbital gland of red deer (Cervus elaphus) calves has been previously associated with feeding and satiety. However, it has been suggested to be most likely affected by some other factor or factors, possibly by excitement of the calf. If so, a calf should open its preorbital gland while being exposed to any stressful procedure. The hypothesis was tested that the preorbital gland is closed in a relaxed calf, whereas it is opened in a stressed calf. Preorbital opening was observed in 41 newborn red deer farm calves during a regular daily routine consisting of a search for newborn calves, their inspection, weighing, and painful marking with an ear tag. The openness of the preorbital gland (preorbital gland closed or opened) was recorded just before manipulation of a lying calf (i.e., in a calm calf) and then during the manipulation (i.e., in a distressed calf). Before manipulation, in all but 3 calves (7.3%, all of which were males), the preorbital gland was closed. All calves observed (100%) opened their preorbital gland during their manipulation, at least by the time the ear was punctured by the ear tag. The proportion of individuals with an open gland was lower (P < 0.001) before than during manipulation (7.3 vs. 100%, respectively). Hence, openness of the preorbital gland in newborn red deer calves was associated with a stressful manipulation by the humans, which suggests that it may be a simple and easily recognized indicator of calf stress.