It’s been a month since we had our dog, Parker, chemically castrated, but for the past week, he’s become very aggressive. In just one week, he’s bitten three people: the first two were a delivery driver and my neighbour, whom he knows very well, and his third victim was a friend we see occasionally. I asked a friend to come over to the house to test the dog’s reaction; he eventually accepted him after about half an hour. I should clarify that my dog has never been mistreated or anything like that. I’ve socialised him well with other dogs (specifically friends’ dogs at get-togethers, both males and females, and we’ve never had a single problem). I’m starting to wonder if the implant he was given a month ago might have something to do with it. I’ve got an appointment with a dog behaviourist this week, but I’d like to know if anyone else has encountered this same issue. Thanks for any advice or stories you can share.
Parker (Majorca Mastiff) and his owners.
Translated from French
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That’s exactly what I went through with my miniature dachshund after he had the implant: he became hyper-aggressive with other dogs and couldn't stand puppies anymore. I had it removed (under general anaesthetic, which is no small thing!) and his behaviour improved significantly: he’s more confident and much less aggressive. Thanks for the explanation, because nobody warns owners that chemical castration can be a total nightmare.
That’s right, the implant you’ve had put in your dog is starting to take effect, which means it’s suppressing his testosterone levels. It’s worth noting that testosterone is regulated by a part of the brain called the hypothalamus, which itself is part of what we call the paleo-limbic brain that controls instinctive behaviours. By shutting down testosterone production, the hypothalamus becomes more active as it tries to produce the hormone in response to the "deficiency" signals it’s receiving from other parts of the brain. When the hypothalamus is overactive, those instinctive behaviours can become more pronounced. Fear, anxiety, and a lack of self-confidence are all emotions managed in part by the hypothalamus—specifically the paleo-limbic system. This drop in testosterone is currently causing an emotional imbalance in your dog, which is manifesting as aggression, whereas before, the testosterone was actually helping him maintain his emotional stability.
What bothers me about what you’re saying is that I’m not at all sure that chemical neutering makes any difference to potential weight gain...
I vividly remember my vet saying to me after my dog was permanently neutered: "Don't worry about the weight, he’s already been on the chemical one for 8 months!" So, I’d assume that if there is weight gain, it’s the same whether it’s chemical or permanent.
Unfortunately, you can’t go back now, so don't panic (I’m sure this little mood swing will settle down), but do book an appointment with a different vet to chat about all this. I’m afraid you might find you have to cut down his food portions...
If Parker follows the name-letter system, he’s coming up to 2 years old... he’s becoming an adult and his personality is really starting to show. I knew a dog who showed signs of aggression towards other dogs (not humans) about a month or two after getting the implant, but it didn't last. Mine didn't show anything like that (and the others weren't done via the implant). Personally, I think vets sometimes lack a bit of foresight regarding neutering because they don't always consider the dog's maturity... you can go for early neutering to try and prevent aggressive behaviour, but that’s before they turn 1... you can neuter a dog to stop them roaming, so that's later on. But seeing how a male's behaviour develops between 18 months and 2 and a half years, I reckon it's about the worst time to go messing with his hormones (just my personal opinion, not an accusation 😅). Whether it’s due to the implant (which should settle down anyway) or not, you should definitely work with a trainer. He’s not a Chihuahua, so you can't really afford to just wait and see...
Hi there, yes, he follows the letter system and will be 2 in May. I’ve got an appointment with a canine behaviourist. The reason we wanted to keep him intact wasn’t for breeding, just because of his weight and body shape (our last dog, a Presa Canario, had joint problems and died at 9 from a tumour). The other two dogs we had were Mastiffs; after they were neutered, they put on a massive amount of weight even on weight-control dry food, which led to health issues. That’s why we went for chemical castration. He doesn't have issues with other male dogs—he’s actually quite submissive, not dominant—it’s more females in season that make him nervous. The problem is with people (yeah, I know some of them deserve it!). He doesn't want anyone in the house. I’ve found a technique where I hold him by the collar and stroke him to reassure him that everything’s okay, but I can see in his eyes that something’s wrong. Still no word from the vet, she’s in surgery today... anyway, I’m calling another vet tomorrow. I’ve been waiting since last Friday for her to call me back; clearly, my dog and his problems aren’t a priority for her. Anyway, the behaviourist is coming on Thursday, so we’ll see how he reacts and he'll tell me what needs to be done.
If Parker’s name follows the 'letter of the year' system, he’s coming up to 2 years old... he’s becoming an adult and his personality is really starting to assert itself.
I knew a dog that showed signs of aggression towards other dogs (not humans) about 1 or 2 months after getting the implant, but it didn’t last. My own dog didn’t show any signs like that (and my others didn't go down the implant route).
Personally, I think vets fall a bit short sometimes because they don’t always take the dog’s maturity into account when discussing neutering... you can go for early castration to try and prevent aggressive behaviour from developing, but that’s before they’re a year old... and you might neuter a dog to stop them roaming, which is usually done later. But seeing how a male dog’s behaviour develops between 18 months and 2 and a half years old, I reckon it’s about the worst time to be messing with their hormones (that's just my personal opinion, I’m not having a go at anyone! 😅).
Whether it’s because of the implant (and it should settle down eventually anyway) or not, you should definitely work with a trainer. He’s not a Chihuahua, so you can’t really afford to just wait and see what happens...
Hi, a chemical castration can lead to an increase in aggression in the days following the insertion due to a temporary spike in testosterone levels in the blood. This doesn't seem to be the case for your dog, though, as he became aggressive three weeks after getting the implant. On the contrary, chemical castration is actually supposed to make a dog calmer after a few weeks. The change in behaviour might therefore be down to something other than the implant itself. You've made the right call by contacting a canine behaviourist; they will help you get things back on track with your dog to stop the aggression. You could also give your vet a ring and let them know the situation so they can advise you. Hope this helps, Emeline.
Hi, thanks for your reply. I've left a message for the vet (a new one, as my usual vet passed away 😔) but she still hasn't called me back... When she put the implant in, the new vet told me it would take effect after three weeks. I'm waiting to see the specialist on Thursday.
It’s true that the implant your dog has had is starting to kick in now, which means it's inhibiting his testosterone levels. It's worth noting that testosterone is actually regulated by a part of the brain called the hypothalamus, which is part of the paleo-limbic brain responsible for instinctive behaviours. By stopping the production of testosterone, the hypothalamus ends up working harder to try and produce the hormone because it’s getting signals from other parts of the brain that there’s a shortage. When the hypothalamus becomes more active, those instinctive behaviours can become more prominent. Emotions like fear, anxiety, and a lack of self-confidence are all partly managed by the hypothalamus and the paleo-limbic brain. This drop in testosterone is causing an emotional imbalance in your dog, which is manifesting as aggression, whereas before, the testosterone was actually helping him maintain his emotional balance.
Chemical castration can lead to a spike in aggression in the days immediately following the procedure due to a temporary rise in testosterone levels. However, this doesn't seem to be the case with your dog, as he became aggressive three weeks after the implant was fitted. On the contrary, chemical castration is actually supposed to make a dog calmer after a few weeks.
This change in behaviour might therefore be due to something other than the implant. You’ve definitely made the right call by contacting a dog behaviourist; they will help you get things back on track so that your dog’s aggression can be managed.
You could also give your vet a ring to let them know what’s going on and see what they advise.
