2.3. Anhedonia Test

A stuffed Kong^TM toy (KONG Company, Golden, CO, USA) was placed on the floor of the dogs pen (small, medium, large or extra-large Kong^TM assigned according to dog size as outlined here [52]. The toy was stuffed with a mix of the dog’s own standard dried biscuits, soaked dried chicken pieces (a common dog training aid) with KONG Stuff’n Paste to bind and the large hole was sealed with a 3-cm long piece of hot dog sausage. Ingredients were mixed following the ratio of 2:3 for biscuits to soaked dried chicken pieces, for each 2 “squirts” of Stuff’n Paste, in order to keep the Kong^TM effectively filled the same. All dogs were already habituated to the Kong^TM toys (provided daily in each of the recruited shelters) and it has been shown that dogs habituated to Kong^TM treat filled Kong’s as feeding devices (i.e., dogs behave in a way demonstrating that they expect to get food from it) as opposed to a rubber toy [53], which could have confounded the results. To prevent potential neophobic reactions to the Kong^TM contents, dogs were offered a small amount of the foods used on the day prior to the test to ensure willingness to eat all of them. To limit the impact of appetite, dogs were given the Kong^TM between 15 to 30 min after they had consumed their normal ration of dog food, as hedonically motivated behaviours seem more driven by opportunism and external stimuli (i.e., eliciting cues such as odours) than by states of deprivation [23,54]. To control further for motivation for food, the dogs’ latency to approach their normal ration of dog food (less palatable than treat food used to stuff the Kong^TM) was recorded once for each dog on the day previous to the Kong^TM consumption test. The dog’s behaviour was video recorded using the same setup as for the home pen recordings but was conducted on the day after the home pen recordings were completed. Following 30 min of exposure, the Kong^TM toys were removed from the pen. The filled toys were weighed before being given to each dog and weighed again after to enable calculation of how much food mix was consumed.

N.D.H. and two research assistants (H.H. and Dr G. Miguel-Pacheco), blind to the dogs’ activity budgets, used the video footage of the consumption test to subsequently score: the total time the dog spent interacting with the food toy (defined as paw or muzzle in contact with, or sniffing the Kong^TM, including time stood chewing the food mix but not in physical contact), expressed as a proportion of the total test duration (Kong_Prop_Time); the number of bouts of interaction with the Kong^TM (a bout was considered to have ended when a dog ceased to physically contact the Kong^TM and ceased to chew food retrieved from the Kong^TM, and began again when the dog re-initiated contact with the Kong^TM; Kong_Bout_N), and the duration of each bout (averaged for each dog; Kong_Av_Bout_Time). Data regarding the percentage of the food mix eaten by the end of the 30 min test (% of Kong Eaten) was included as a fourth test variable.