Circadian pattern of acute phase proteins in the saliva of growing pigs

The circadian rhythm of the acute phase proteins (APPs) haptoglobin (Hp) and C-reactive protein (CRP) was assessed in saliva samples from 18- and 21-week old pigs. Saliva was collected at 07.00, 11.00, 15.00 and 19.00 h on two consecutive days and the Hp and CRP concentrations were quantified using two species-specific, time-resolved immunofluorometric assays.Salivary Hp levels were significantly higher (P < 0.001) in the morning compared to late afternoon (0.68 and 0.37 μg/mL, respectively) although the magnitude of the difference was much lower than is produced by inflammatory conditions. No significant differences were observed in CRP concentrations. Although the concentration of both APPs was higher in the 21- compared to the 18-week old pigs (P < 0.0001), no differences were observed in the circadian rhythm of these APPs when the two age groups were compared. Animal gender did not influence the circadian pattern of either APP, although the mean salivary CRP levels were higher in females (P < 0.05).