A synthetic analog of the bovine-appeasing pheromone facilitates adaptive responses during disease in dairy calves

Gastrointestinal and respiratory infections are the main cause of morbidity and mortality in the first months of life in young dairy calves, with an important negative effect on animal welfare and production. Appeasing pheromones act through olfactory pathways to influence stress-related physiological and behavioral responses in mammals and have shown promising results in a variety of domestic animals. A synthetic analog of the bovine-appeasing pheromone (BAP) has been observed to reduce veterinary costs in dairy calves and modulate the clinical expression of respiratory illness, potentially influencing the timing of symptom presentation and immune response in beef calves and young bulls. The objectives of this study were to observe the influence of BAP on disease incidence and recovery in dairy calves, and on physiological and behavioral stress responses during naturally occurring disease episodes. In the present randomized controlled trial, 72 female Holstein Friesian dairy calves were randomly allocated to receive BAP or a placebo once every 2 wk from birth to 4 wk after milk weaning. Clinical disease affected 33 calves, across a total of 44 recorded illness episodes (24 in the BAP group and 20 in the placebo group; no significant difference between groups). Conditions included gastrointestinal infections, respiratory infections, navel infections, and other clinical symptoms such as fever and lameness. It was hypothesized that diseased dairy calves in the BAP treatment would display fewer signs of stress compared with calves receiving the placebo and their recovery would be faster. Calves were equipped with triaxial accelerometers on the hind leg postnatally, and their activity levels were observed throughout the trial. Data on live weight gain was also obtained, and calves were fitted with heart rate monitors every week for at least 24 h to assess heart rate variability (HRV). During periods of disease, BAP was associated with a reduction in the activation of the neuroendocrine system as evidenced by higher HRV parameters, including increased standard deviation of beat to beat of normal sinus beats (SDNN) and root mean squares of successive differences (RMSSD). Calves in the BAP group also displayed a faster recovery of their activity levels and HRV parameters compared with the placebo group. These results suggest a potential welfare benefit of the use of BAP during bouts of sickness.