n male dogs, it is often between 5-12 months of age that unwanted behaviours worsen, and neutering is often the suggested fix, especially if aggression or reactivity is a key factor. Neutering is the last thing to do, instead rule out other factors first! It is no coincidence that this is also when dogs reach their highest levels of testosterone, after which their levels plateau (Pathirana et al., 2012). Whilst many vets have moved on, we need to acknowledge why this was such a popular option and why people may continue to suggest it as a solution. Dog to human aggression will not be fixed with neutering. So far, no studies or evidence link aggression directed toward humans to unneutered dogs. As in cases of dog-to-dog aggression, there are frequently other contributing factors when dogs show aggressive behaviours towards other dogs. Problem behaviours such as roaming in search of an in-season bitch and indoor urine marking are often directly influenced by testosterone and could be improved by chemical or surgical castration (Hart and Eckstein, 1997). Should I get my dog sterilised, and if so, what age is best? Before rushing to the vets, let large breed dogs fully grow, around 2-years old, before castrating. Consider this study by the University of California. They looked at 795 golden retrievers and found a significant increase in hip dysplasia and cruciate ligament rupture in neutered dogs, primarily seen in those sterilised before one year old. Neutered large-breed dogs suffer more bone and spleen cancers than those who are not. This doesn’t mean don’t sterilise ever, but just wait a little longer. In fact, the University of Georgia conducted a 20-year study from 1984 to 2004 on more than 40,000 dogs. They found that neutered dogs lived an average of 9.4 years, compared to those not neutered, who lived on average 7.9 years. One explanation may be that testosterone can increase risk-taking behaviours (Stanton, Liening &Schulthesis, 2011). Won’t castration stop my dog from humping? Humping and mounting can be a stress response or, occasionally, an attention-seeking behaviour, and despite castration, learning can maintain the behaviours; behaviour modification is more successful in these cases. Will castration fix my issue with my dog chasing other animals? Castration is unlikely to change predatory behaviour such as inappropriate chase or hunting and killing wildlife. These will need to identify and address the underlying cause of the problem behaviour. Although there are cases where castration could have a beneficial effect on behaviour or no effect at all, there are a few situations in which castration could potentially cause or exacerbate the problem. So why is castration still suggested frequently? Testosterone can lower the threshold at which aggressive behaviours are used and increase their intensity. Its effects on several other behavioural traits, such as increased vigilance and responsiveness to threats, behavioural persistence and risk-taking behaviours, can increase the likelihood of an animal responding to a threat with aggression (Terburg and van Honk, 2013). Therefore castration can potentially reduce the possibility of a male dog exhibiting aggression in reaction to perceived threats. In all cases of aggression, any sterilisation must be combined with a comprehensive behaviour modification plan to address the dog’s underlying emotional state and the triggers that cause him to show distance-increasing behaviours. Is Chemical Castration a Better Option? In short, no. Chemical castration should not be an option if the dog shows any aggression. The risks of it worsening for the first few months are too high. The implant company say testosterone levels initially rise and then decline over 4-6 weeks. Still, one of the most common reported side effects is that this increase can last for around three months on average. The product takes 6-12 months to wear off. From a behavioural perspective, it is far better to opt for surgical castration if testosterone contributes to the undesired behaviour. Did castration make my dog fearful? Circulating testosterone is associated with increased self-confidence and reduced fearfulness (Terburg and van Honk, 2013), so castration can potentially increase fearfulness in already nervous dogs. It doesn’t mean it is the cause of the fearfulness but could contribute to the length of time it takes to improve the problem behaviours. What should I do? If you are worried about your dog’s behaviour, work with a behaviourist and your vet together. Whilst we cover the whole of the UK with our consultations, you must find someone you connect with, so we recommend you search on the APBC, CCAB or IAABC websites for reputable behaviourists under the Animal and Behaviour Training Council.