Table 1.

Studies examining effects of auditory enrichment on canine health and behavior.

Authors, Year, Ref	Population	Location	Intervention	Measures	Result
Wells, Graham, Hepper 2002 [13]	n = 50 male: 27 neutered female: 23 spayed Age from 6 m–6 y mainly cross-bred	Rehoming Center, UK	Five treatments: 1. Control; 2. Human conversation (radio program); 3. Classical music (mix of tracks); 4. Heavy metal music (mix of ‘Metallica’ tracks); 5. Pop music (mix of tracks). Dogs exposed to each of the five interventions on five separate days, with one day rest in between. Acoustic stimuli presented between 10:00–14:00.	Three behavioral parameters observed: Position in kennel, activity, and vocalization. Dogs observed at 10 min intervals for duration of intervention.	More time spent at front of kennels during all auditory interventions. Changes in activity and vocalization related to type of auditory stimulation—more time resting and quiet when exposed to classical music. Increased barking during heavy metal music exposure.
Kogan, Schoenfeld-Tacher, Simon 2012 [14]	n = 117 Two groups: 1. rescue dogs male: 21 neutered female: 12 spayed, 1 entire Mean age 5.27 y Dachshund (pure and cross) 2. short-term boarding male: 31 neutered, 10 entire female: 38 neutered, 4 entire Mean age 5.92 y Variety of pure and mixed breed	Dog shelter and boarding facility, USA	Four treatments: 1. Control; 2. Classical music (4 tracks); 3. Heavy metal music (3 tracks); 4. Dog relaxation music (Through a dog’s ear (TADE)). 45 min exposure, followed by a 15 min break. Three conditions tested per day between 09:00–12:00 Dogs exposed over 4 months, not all dogs exposed to all treatments.	Three behavioral parameters observed: Activity, vocalization, and body shaking. Dogs observed at 5 min intervals for duration of intervention.	No interaction between treatment and group (rescue vs. boarding dogs), although rescue dogs spent more time sleeping and silent. Changes in activity and vocalization related to type of auditory stimulation—more time sleeping and quiet when exposed to classical music. Increased body shaking during heavy metal music exposure.
Bowman, Dowell, Evans, Scottish 2015 [12]	n = 50 male: 25 neutered, 9 entire, female: 12 spayed, 4 entire Age from <1 y to >10 y Variety of breeds, high proportion of Staffordshire bull terriers Aggressive dogs excluded	Animal rescue and rehoming center, Scotland	Two treatments: 1. Control; 2. Classical music (mixed tracks, low pitch and slow tempo) Dogs exposed to one treatment for 7 days, then the alternate treatment for 7 days. Acoustic stimuli presented between 10:00–16:30.	Three behavioral parameters: Position, location, and vocalization. Heart rate variability. Salivary cortisol. Observations made for 1.5 h, 2x/day (10:30–12:00 and 14:00–15:30), on days 1, 7, 8 and 14. Saliva collected at the end of each 1.5 h period.	Classical music exposure induced changes in behavior (less time standing and barking) and altered heart rate variability, indicative of reduced stress. No significant changes in salivary cortisol. Resistance to effects of music if the same playlist is used repeatedly. Therapeutic effects of music more obvious in male dogs.
Brayley, Montrose 2016 [15]	n = 31 male: 24 neutered female: 7 spayed Age from 9 m to 13 y	Rescue shelter, UK	Five treatments: 1. Control; 2. Audiobook; 3. Classical music (Beethoven); 4. Pop music (mix of tracks); 5. Dog relaxation music (TADE). Dogs exposed to each treatment for 2 h, with 2 days rest in between. Acoustic stimuli presented between 10:00–12:00.	15 behaviors sampled, including multiple measures of activity and vocalization. Behavior recorded every 5 min using an ethogram.	Audiobook treatment induced calmer behavior than all other treatments. Classical music induced calmer behavior than pop music and no intervention (control).
Albright, Seddighi, Ng, Sun, Rezac 2017 [16]	n = 10 male: 8 neutered, 2 entire Mean age 4.2 y Beagles	Veterinary hospital, USA	Five treatments: 1. negative control (saline); 2. positive control (sedative); 3. Human voice quiet (55–60 dB); 4. Human voice loud (80–85 dB); 5. Dog relaxation music (TADE) (45–50 dB). Dogs exposed to treatment for 20 min after sedative injection. Each dog exposed to all treatments with a minimum of 48 h rest in between. Testing between 08:00–15:00	Depth of sedation assessed by spontaneous behavior, accelerometry, and restraint tests. Behavior assessed every 5 min and compared before, during and after treatment. Restraint tests 30 min and 40 min post-treatment	Sedation is negatively impacted by high-intensity noise conditions (80–85 dB) Exposure to music marketed as having a calming effect in dogs did not improve sedation
Bowman, Dowell, Evans, Scottish 2017 [17]	n = 38 male: 15 neutered, 9 entire, female: 7 spayed, 7 entire Age from <1 y to >8 y Variety of breeds, high proportion of Staffordshire bull terriers	Animal rescue and rehoming center, Scotland	Six treatments: 1. Control (before and after); 2. Soft rock; 3. Motown; 4. Pop music; 5. Reggae music; 6. Classical music Dogs exposed to a different music treatment each day for 5 consecutive days. Acoustic stimuli presented between 10:00–16:00.	Three behavioral parameters: Position, location, and vocalization. Heart rate variability. Urinary cortisol. Observations made for 1 h, 2x/day (10:30–11:30 and 14:30–15:30). Urine collected between 13:00–14:00 on days 1, 4–8 and 11.	Music exposure (all genres) induced changes in behavior (less time standing) and altered heart rate variability, indicative of reduced stress. Urinary cortisol higher during soft rock exposure. Physiological and behavioral changes were maintained over the 5 d of auditory stimulation, suggesting that providing a variety of different genres may minimize habituation.
Engler, Bain 2017 [18]	n = 74 no further information supplied.	Veterinary teaching hospital, USA	Three treatments: 1. Control; 2. Classical music; 3. Dog relaxation music (TADE) Treatment rooms assigned to each treatment. Music played continuously throughout the day. Each dog only exposed to a single treatment (control = 30, music = 23, TADE = 21)	Owners and clinicians completed a standardized survey regarding dogs’ behavior. Physiological variables obtained from the medical record.	No difference in behavior (aggression, anxiety) or physiology (body temperature and heart rate) of dogs detected. Classical music had a positive effect upon owner and employee satisfaction.
Alves, Santos, Lopes, Jorge 2018 [19]	n = 67 males: 34 females: 33 Puppies (7 weeks old) Four different breeds (27 German shepherd dogs, 19 Belgian Malinois shepherd dogs, 7 Dutch shepherd dogs, and 14 German shepherd dog and Belgian Malinois shepherd dog crosses).	Police canine unit, Portugal	Two treatments: 1. Control (n = 46); 2. Varied auditory stimulation (including music, radio talk shows, and environmental noise (cars, sirens, gunshots)) (n = 21) Auditory stimulation provided from 3 weeks of age for 2 h/day, focused around meal and play time.	Puppies’ performance in a skills test (9 scenarios ranging from following and submission to startle response and pain sensibility) evaluated at 7 weeks of age.	Auditory stimulation had a negative effect upon puppies’ performance overall, in particular on following, lifting by evaluator, and submission tests.
Koster, Sithole, Gilbert, Artemiou 2019 [20]	n = 16 (8 kenneled, 8 student-owned) male: 5 female: 11 Mean age 3 y 81% mixed breed	Veterinary teaching hospital, West Indies	Two treatments: 1. Control; 2. Dog relaxation music (TADE) All dogs exposed to one treatment for a 60 min veterinary training session, then 7 days later exposed to the alternate treatment.	Heart rate variability	Auditory stimulation reduced RR variability, suggesting the novel music exposure had an excitatory rather than a calming effect.