Inter-Dog Aggression Between Two Entire Male Dogs, As a Result of Sexual Maturation and Subsequent Alteration in Social Dynamics: A Case Study

Abstract This case study documents a male entire Labrador, Percy, that was presented at 3-years-old, due to a 2-year history of confrontational behaviour towards a resident entire male dog, Dennis. Percy had demonstrated significant aggressive behaviour, resulting in physical injury, towards Dennis during the oestrus period of a resident female entire dog. Since that time, Percy had shown repeated, intense, aggressive behaviours towards Dennis, which were increasingly difficult to interrupt or prevent, resulting in partial separation. A behavioural modification plan, including safe separation of the two dogs, muzzle training, environmental optimisation, psychopharmacology with fluoxetine and gabapentin, and chemical castration, was essential to facilitate meaningful improvement. Percy was able to be safely managed within the home and start a gradual counter-conditioning programme with Dennis, highlighting the importance of a multifactorial approach, including how neutering discussions may be needed in complex cases. The timing, onset, and maintenance of the aggressive behaviour in this case illustrate how hormonal development and puberty can impact behaviour and the important role veterinarians and veterinary behaviourists play in discussions surrounding neutering. When and if to neuter our companion animals continues to be a contentious discussion and includes decisions surrounding the presence of desirable or undesirable behaviour, resident conspecifics, human preferences, education, and medical factors. Through illustration of the important role social dynamics and reproductive behaviour can play in undesirable behaviour, this case provides support to practitioners navigating behavioural cases where they are playing a part. Information © The Authors 2026