Biological variation of cortisol level in milk of domestic goats in natural habitat

The purpose of the study was to determine the milk cortisol range of free-living domestic goats (Capra hircus) and to assess the potential influence of individual and environmental factors on the physiological level of the hormone. Milk samples from five goats were collected during morning and evening milking during a 10-week monitoring period (from August to October). 416 milk samples were collected and aliquots were applied onto a cellulose membrane, dried, and transported to the laboratory for quantitative enzyme-linked immunosorbent assay (ELISA). The milk cortisol concentration reached 76…116 nmol/l. Moreover, the observed intra-individual variation of the milk hormone was significantly higher (53 %) than the inter-individual variation (26 %). A significant increase of milk cortisol (up to 330…460 nmol/L) was found for a sick animal several days before death. During the data analysis, there were no significant correlations between the cortisol level and the age of the animal, the milk volume milked per one milking, the time of milking and the time of waiting for milking. However, significantly lower levels of the hormone were observed for the first animal in line for milking compared to the second, and significantly higher levels were observed for the second animal compared to all others. It is therefore assumed that the current psychoemotional reactions associated with social interaction – both within the species and with humans – may have a determining effect on the milk cortisol level of domestic goats. They may make a greater contribution to the variation of the hormone level than circadian rhythms and age, fullness of the mammary gland.

cortisol, domestic goats, ELISA, milk, stress