Behavioural effects of ovariohysterectomy on hitches

A questionnaire about their dogs' behaviour was administered to the owners of 150 spayed bitches at the time of spaying and again six months later. It was also administered twice with the same time interval to a control group of 150 unspayed bitches, group matched for breed and age. Principal component analysis of the questionnaire responses yielded 13 factors. On two of these factors, ‘indiscriminate appetite’ and ‘dominance aggression towards family members’, the scores of the spayed bitches showed a significant increase compared with their controls. The spayed bitches most likely to show an increase in dominance aggression were puppies under one year, already showing some aggression.