Working dogs spend a large amount of their time in cars. It has been assumed that a larger compartment in the car would be more comfortable for the dog, but that a smaller space could be safer. This hypothesis was tested in a study from The Swedish University of Agricultural Sciences.
German Shepherds (N=8) and Springer Spaniels (N=8) from the Swedish Police and Customs were tested in four different car cage sizes; two cages were the minimum size allowed according to Swedish regulations for private and working dogs respectively, and the other two cages were one larger and one smaller than these. Cages were tested during normal driving as well as slow cruising. During normal driving, the heart rate was higher and behavioural stress indicators more frequent regardless of cage size. In the three smaller cages there were fewer overall movements and body position changes, when compared to the largest cage size. That this could be a sign of decreased comfort is supported by the finding that dogs could not turn around in these cages without curving their back upwards or lowering their rump. This could have negative physical effects, especially in German Shepherds which are predisposed to musculoskeletal disease. Furthermore, German Shepherd dogs showed more bracing postures, in the cage size which was shorter than their own body length. However, this bracing did not result in them losing their balance any less often, implying that a smaller cage is not necessarily safer.
https://doi.org/10.1016/j.applanim.2018.05.028
Skånberg, L., Gauffin, O., Norling, Y., Lindsjö, J. and Keeling, L.J. (2018) Cage size affects comfort, safety and the experienced security of working dogs in cars. Applied Animal Behaviour Science, 205: 132-40.