L'impatto dello stress da trasporto sul cortisolo salivare nei bovini

The concept of animal welfare has changed over the years. Recently, the European Commission has promoted a revision of the existing legislation on animal welfare to align it with the latest scientific evidence. For this purpose, it is fundamental to define welfare indicators to objectively evaluate the animals’ status. Several approaches are reported in the literature, ranging from field assessment of their behavior to laboratory analyses of their primary metabolic and hormonal patterns. Particular emphasis is placed on cortisol, given its prominent role in mammalian responses to reduced welfare (stress). Currently, the method mainly used to analyze the hormone is to measure its concentration in blood plasma. However, its collection can induce a significant stress response, thus altering the consequent results. Therefore, to achieve reliable measurements of cortisol levels, alternative and noninvasive matrices such as saliva, feces, and hair are being investigated. Salivary cortisol is highly correlated with plasma cortisol, of which it reflects the shift in hormone levels with a time-delay that has been reported to be of around 30 minutes in cattle, thus providing more reliable results. Cortisol located both in fecal and hair matrices has been defined as an indicator of a chronic stress situation as it gives a reliable and valid reflection of a long-term secretion of the hormone. In this context, the present experimental study aimed at evaluating the impact of transportation, identified as a known stressor, on the cortisol level in bovine saliva. The trial involved animals from the integrated France-Italy beef production system. Saliva samples were collected from a total of 20 bulls ranging from 11 to 18 months of age: 10 of them had just transported to the farm from different herds located in France (test group); the other 10 had already been housed on the farm for at least 60 days and were therefore recognized as unstressed (control group). Saliva samples were taken from the first group up-on arrival on the farm, continuing over the next 8 hours at five different time intervals, and from the second group at three different time intervals. Saliva samples were analyzed in the laboratory by enzyme immunoassay (EIA) to measure salivary cortisol levels. The results showed that salivary cortisol concentrations did not vary among animals in the same group. For the test group, the results revealed that salivary cortisol levels began to drop significantly only after 2 hours after arrival on the farm. On the contrary, for the control group, salivary cortisol levels did not change significantly over the sampling period. However, some outliers, due to the temperament of a few individuals, were found in the trend of salivary cortisol concentration within each group. At last, comparison between the two groups showed a difference (p = 0.003) in salivary cortisol levels, indicating that transport led to an increase in the concentration of the hormone in the bulls’ saliva. These findings reveal that animals need several hours for cortisol secretion to return to normal after exposure to an important stressor such as transportation. Moreover, the results demonstrate the reliability of salivary cortisol for stress assessment in cattle. To conclude, this study may represent the first step to help farmers and veterinarians perform objective and on-field monitoring of acute stress levels in animals and improve their welfare conditions.