Salivary cortisol in healthy dogs: a randomized cross-over study to evaluate different saliva stimulation methods and their effects on saliva volume and cortisol concentration

BACKGROUND: Salivary cortisol collected at home is a useful test to diagnose and monitor Cushing’s syndrome in humans. The main problem in dogs is to retrieve a sufficient amount of saliva. The aim of this study was to evaluate different salivary collection methods and compare their effects on volume, pH and cortisol concentration of saliva. Sixteen healthy Beagles were used in a 4 × 4 randomized crossover study with a washout period of 1 week between each of the following collection methods: 1. Salimetrics® cotton swab dipped in ginger powder (ginger group); 2. beef-flavored Salimetrics® (bouillon group); 3. Salivette® cotton swab with an enclosed treat (treat group); 4. plain Salimetrics® (control group). First, baseline saliva (plain cotton swab, S0) and, 2 min later, experimental saliva (according to group allocation above, SExp) were collected. Saliva was gathered by holding the swabs in the animal’s mouth for 2 min. After the cross-over study, another saliva sample was collected from all dogs by the ginger method, using a 30 s sampling time (30s-ginger method). Cortisol concentrations were measured by liquid chromatography tandem mass spectrometry. RESULTS: All three stimulation methods increased saliva production significantly (S0 compared to SExp: ginger p = 0.0005; bouillon p = 0.009; treat p = 0.007). Only ginger stimulation, however, generated a significantly higher amount of saliva (SExp) compared to the control group (p = 0.00001; median (range) amount of saliva for SExp: ginger 1200 ul (600–1700), bouillon 650 ul (200–1900), treat 700 ul (300–1000), control 400 ul (0–1100)). The amount of saliva retrieved by the 30s-ginger method was still higher than that from the control group (p = 0.0004). Bouillon and treat stimulation led to decreased pH values (bouillon, p = 0.0028; treat, 0.0018). Excitement was higher in the ginger group (p = 0.01). Chewing was intensified in the ginger and treat group (ginger, p = 0.003; treat, 0.0009). The cortisol concentration SExp was higher compared to that of S0 in the ginger and treat group (p = 0.02, 0.003). The experimental cortisol concentrations (SExp) were not different between groups. CONCLUSIONS: The 30s-ginger method could prove useful in evaluating or monitoring dogs with Cushing’s syndrome, as sampling at home for 30 s by the owner seems feasible.