Daily Cortisol Profile in Lactating and Non-Lactating Dairy Goats (Capra hircus)

The objective of the present study was to determine the daily plasma cortisol pattern in domestic lactating and non-lactating goats. In a total of 12 multiparous goats (6 lactating, 6 non-lactating), 4 daily blood samples were taken over the course of 12 days, beginning at different times, in order to cover two, 24 h periods. Lactating goats were at their 4th month of lactation and were hand-milked daily at 07:30-08:30 h since parturition. Repeated measures ANOVA, Tukey-Kramer and student’s t-tests were used, considering diurnal (07:00-18:00 h) and nocturnal hours (19:00-06:00 h) as well as the condition of lactation. Higher levels of cortisol (45 nmol L 1) were found during diurnal hours, followed by important and sustained decreases (6-16 nmol L 1). A pair of smaller peaks appeared between 23:00-24:00 h, followed by a decrease that was maintained until 06:00 h, at which time high levels of cortisol returned (26 nmol L 1). Daily average cortisol values were similar between lactating (16.6 1.8) and nonlactating goats (16.5 1.8; nmol L 1; p>0.05). Diurnal cortisol was higher (p = 0.003) than nocturnal (19.6 1.9vs. 13.5 1.1 nmol L 1). Daily cortisol levels are similar between lactating and non-lactating domestic goats at their fourth month of lactation and cortisol levels undergo significant changes during the day, with higher concentrations in diurnal compared to nocturnal hours.