The circadian rhythm of cortisol in the saliva of young pigs

Single and population-mean cosinor analyses document a circadian rhythm in salivary cortisol of pigs (p < 0.001). The midline estimated statistic of rhythm, the MESOR (M), is 1.50 ± 0.07 ng/ml. For the group of 14 pigs studied there was a predictable Variation of 64% around this mean in salivary cortisol within a day: the double circadian amplitude, 2A, was 0.96 ng/ml, with a 95% confidence interval ranging from 0.60 to 1.32 ng/ml. A measure of timing, the acrophase, ∅, was 10 h 52 min from the phase reference (0030, the middle of the daily dark span of the 24-h light-dark cycle in which the pigs were kept). The 95% confidence interval of ∅ extended from 9 h 48 min to 12 h 12 min from the reference time. The chronobiologic approach provides indispensable quantitive characteristics as reference standards for future basic or applied work.