Limitations of salivary and blood cortisol determinations in pigs

Blood and saliva samples were taken from groups of pigs maintained in intensive conditions. Multiple samples were taken from two unrestrained pregnant sows fitted with jugular cannulae. Single samples were taken from groups (mixed gilts and entire males; 70-90 kg) which were lightly exercised (7) or restrained (12). The rate of salivary secretion was low and collection of adequate samples took 5 min; in a number of pigs no saliva could be obtained. In order to stimulate salivary secretion, pigs (70-80 kg) were injected with pilocarpine nitrate (25 mg, subcutaneous) which produced a copious flow of saliva persisting for at least 15 min. Resting sows had higher mean levels of cortisol in plasma, ultrafiltrate and saliva than the other groups, which did not differ from each other. Within the pilocarpine group, males had a higher ultrafiltrate level of cortisol than females. In most instances salivary cortisol was significantly greater than ultrafiltrate cortisol. Ultrafiltrate and plasma cortisol were highly correlated (r = 0.883) but this correlation was low in the presence of pilocarpine (r = 0.260). Salivary cortisol was poorly correlated with either plasma (r = 0.167) or ultrafiltrate cortisol (r = 0.278) and the correlation with plasma was even lower following the administration of pilocarpine (r = 0.086). It was concluded that salivary estimates of cortisol in the pig were not usefully correlated with levels of ultrafiltrate (free) cortisol.