Central Regulation of Stress Response in Cattle

Abstract

Useful and biologically meaningful determinants of stress of farm animals at the field level do not exist at present, though quantitative measurement of stress is essential for the farm animals' well-being. At laboratory level using rodents, physiological and behavioral changes induced by stressors and its regulation by the central nervous system have been elucidated in considerable detail. However, it remains unclear whether we could apply that knowledge to species other than rodents. Therefore, we studied several neurotransmitters involved in the regulation of stress response in cattle. Examination of the effects of intracerebroventricularly administered neurotransmitter candidates revealed which component of stress response was induced or reduced. Thus, we identified several stress-inducing neurotransmitters and one stress-reducing neurotransmitter in cattle, and suggested that the regulatory roles of the neurotransmitters on stress response differ from those of other species, as well exemplified by rodents. Furthermore, for the stress-reducing neurotransmitter, oxytocin, we showed for the first time the association between individual differences in behavioral and hypothalamic-pituitary-adrenal (HPA) axis reactivity to acute stressors and basal levels of plasma oxytocin concentration and its reactivity to the stressors. This suggests that oxytocin may be a neurobiological candidate involved in individual differences for stress susceptibility in cattle. Currently, we are examining the association between polymorphism of oxytocin-related genes and individual differences in stress susceptibility. This knowledge will help improve animal welfare by allowing genetic selection for adaptability to the environment.