Objective: To describe changes in WBC counts, plasma cortisol concentration, and fecal parasite shedding of dogs housed in an animal shelter and determine the effects of daily petting sessions on these variables.

Design: Hybrid prospective observational and experimental study.

Animals: 92 healthy dogs newly arrived to an animal shelter and 15 healthy privately owned dogs (control group).

Procedures: Blood and fecal samples were collected from shelter dogs 1, 3, and 10 days after arrival and from control dogs once. A subset of shelter dogs (n = 15) was assigned to receive 30 minutes of petting daily. Plasma cortisol concentration was measured, CBCs were performed, and fecal samples were evaluated for parasite ova.

Results: For shelter dogs, total leukocyte, neutrophil, and lymphocyte counts increased significantly between days 1 and 10, with less consistent increases in monocyte count and neutrophil-to-lymphocyte count ratio. Parasite shedding was unaffected by duration of shelter stay but was greater for shelter versus control dogs. For shelter dogs, plasma cortisol concentration decreased with time and was higher than that of control dogs on each day. Total leukocyte, neutrophil, and monocyte counts and neutrophil-to-lymphocyte count ratios were also higher for shelter versus control dogs. Petting sessions resulted in a decrease in plasma cortisol concentration but in no other variables.

Conclusions and clinical relevance: Large increasing immunologic responses, heavy parasite shedding, and high but decreasing plasma cortisol concentration were identified in shelter dogs. Daily 30-minute petting sessions affected only cortisol values, so the clinical importance of petting for immunologic and other health outcomes remains unclear.