Urinary posture and motor laterality in dogs (Canis lupus familiaris) at two shelters

• Most studies of motor laterality in dogs have focused on staged forelimb tasks.
• We examined instead the hindlimb raised when urinating during walks of shelter dogs.
• Propensity to raise a hindlimb varied with sex and age, but not reproductive status.
• We found no evidence of a population hindlimb bias and most dogs were ambilateral.
• Use of a natural hindlimb behavior to assess laterality has benefits and costs.

Motor laterality is the preference shown for using one limb or lateral half of the body over the other. In domestic dogs, most laterality studies have examined forelimb preferences during staged tasks. We focused instead on hindlimb preferences during urination when males use the raised-leg posture and females the squat-raise. We observed individual dogs during walks at two shelters (Tompkins County SPCA and Cortland Community SPCA) and recorded posture used for each urination and hindlimb raised, if any. First, we examined whether raising a hindlimb during urination varied with sex, age class, or reproductive status (females, anestrous intact or spayed; males, intact or neutered). Second, for dogs that raised a hindlimb during urination, we determined whether a population bias existed. Finally, for dogs with at least 10 urinations in which a hindlimb was raised, we examined whether a significant hindlimb preference existed. For some analyses, we had sufficient dogs at only one shelter. We found that males were more likely than females to raise a hindlimb during urination (P < 0.0001 at each shelter), and that propensity to raise a hindlimb was unaffected by reproductive status (P = 0.82, Cortland). Seniors were more likely than adults, which, in turn, were more likely than juveniles, to raise a hindlimb during urination (P < 0.0001, Tompkins). We found no evidence of a population bias with respect to hindlimb raised at either shelter (% of hindlimb raises involving the right hindlimb: 53%, Tompkins; 43%, Cortland). Of the dogs that met the criterion for at least 10 urinations with a raised hindlimb, most were ambilateral (83%, Tompkins; 90%, Cortland). Our study confirms and extends for shelter dogs the effects of sex and age on urinary postures previously reported for dogs living under other conditions; to our knowledge, the increased likelihood of raising a hindlimb during urination that characterized seniors (males, 91%; females, 25%) when compared to adults (males, 73%; females, 6%) has not been reported previously. Lack of a population bias with respect to hindlimb raised is consistent with findings of most motor laterality studies in dogs. However, our finding that most dogs were ambilateral differs from results obtained from studies using staged forelimb tasks. Assessing motor laterality for a natural hindlimb behavior in dogs during walks has both advantages and disadvantages, which include ease of observation during a positive experience for the dog and the challenge of obtaining sufficient scores for each dog.