4 Crucial Reasons Why My Dog’s Behaviour Changed in a Big Way

why my dog's behaviour changed

Are you finding yourself asking “Why my dog’s behaviour changed”? We take a deep dive into the four main reasons for a dog’s behaviour change and what you can do about it.

Dog behavior is a well-documented area of study. We all know our dogs well and do not need to be dog whisperers or canine behaviourists to know that our “soul mutt” is behaving differently than we are accustomed to.

So, what factors lead to changes in a dog’s behaviour? This guide explores some of the main reasons behind canine behavioural changes.

changes in a dogs behavior
A dog’s behaviour can change suddenly due to health issues, trauma, hormones, depression, pain and gaps in their training, particularly under-developed life skills.

Why My Dog’s Behaviour Changed – 4 Factors That Can Cause Behavioural Changes in Dogs

sudden behavior changes in dogs
Pain is a common cause of sudden behaviour change in dogs.

1.   Health Issues

Health issues can impact a dog’s eating patterns and urinary and defecation behaviours. All these changes could indicate pain or underlying issues that can range from simple infections to serious disorders like kidney disease, cancer, hip dysplasia etc.

If your dog is an adult, you probably already know about their routine behavior.

 Still, it can help to spend some more time observing your dog. Ask yourself the following questions:

  • Is your dog walking differently (like a drunk)? If so, it may need a complete neurological exam and/or blood tests. Your vet will check for hypoglycaemia, dehydration, electrolyte imbalance, signs of stroke, chemical toxicity, etc.
  • Is s/he acting confused or disoriented? In addition to the above, your vet may look for visual or hearing issues.
  • Has your fur baby started obsessively licking itself or eating unusual things? Your vet will conduct an oral exam of the dog and also evaluate its diet. It could be due to dietary insufficiencies.
  • Is it suddenly aggressive? – a normally sweet and stable dog could snap, growl, or bite for no reason due to pain or trauma.

Often dogs’ behaviours are difficult to replicate in front of the veterinarian. If needed, film the behaviour at home to show it to your vet. If the changes cannot be explained by the usual tests and visual exams, your vet may even order CAT scans to rule out brain-related issues.

2.   Anxiety or Stress

why my dog's behavior changed
Anxiety and stress in dogs can manifest as destructive behaviour and soiling in the house.

Dogs can experience stress and anxiety due to several reasons.

  • Change in routine – dogs love routine and any change in it can be extremely stressful for them. Once walking, feeding, and naptime routines are established, changes can upset your dog’s physical and mental well-being. Due to these changes, a dog might become aggressive or destructive. Some dogs start barking excessively or may become destructive. This is why Foresight Dog Trainers do not recommend establishing routines and instead vary up a dog’s day so they don’t suffer from the stress of anticipating feeding, walking, playtime etc. A flexible dog is much easier to live with and less prone to anxiety.
  • Separation anxiety – many dogs suffer from this, especially if they are left alone for prolonged periods. Dogs with extreme separation anxiety may show appetite changes, and fear (hiding, trembling, etc.), or bark excessively while the owners are away. The first step in creating a behaviour modification plan for separation anxiety is to introduce crate training. Crate training increases a dog’s independence and provides a positive, safe space where the dog can rest and work through passive calming activities.
  • Fear of loud noises– fireworks, lightning and thunder, or construction or vehicular noises can also stress out some high-strung dogs. Dogs with this type of anxiety may hide, urinate or defecate indoors, bark at noises, etc. Through counterconditioning and desensitisation, a dog’s fear of loud noises can be transformed. Similarly, such dogs often lack confidence and optimism, through games-based dog training, these life skills can be improved.

3.   Lack of Exercise and Training

why has my dogs behaviour changed suddenly
Bored dogs can become destructive dogs. Destructive behaviours can be directed towards household objects, other dogs and even obsessive-compulsive behaviours like foot licking and chewing.

Dogs need regular mental and physical exercise to stay healthy and happy. Even small breed dogs need at least 15-20 minutes of physical activity once or twice a day to prevent restlessness, boredom, depression, and anxiety symptoms described above.

If your dog is used to a great deal of exercise and that activity is suddenly reduced, then your pet may resort to other forms of exercise or even bark excessively or destroy things to compensate.

Keep your dog busy and mentally stimulated with food puzzles, stuffed Kongs, snuffle mats, long-lasting chews, scent games and licky mats.

Likewise, early dog training since puppyhood is especially important to prevent behavioral issues in adulthood. Every dog, irrespective of its breed and size, needs benefits from some basic obedience training in simple commands like stay, heel, sit, come, drop it, etc. More importantly, puppy and dog training solutions should include a life skill program that develops confidence, optimism, flexibility, independence, focus, calmness, and tolerance to frustration.

why my dog's behaviour changed
An imbalance between the energies of dogs in a multi-dog household can expose age-related behavioural changes.

As a dog ages, it could show several behavioural changes such as:

  • Decreased activity and increased sleeping (adult dogs need around 14 hours of sleep each day, while puppies need about 20 hours)
  • Increased anxiety, especially if a dog has vision-related problems or hearing issues
  • Incontinence which could result in indoor soiling
  • Pickiness about food or appetite changes
  • Cognitive decline – confusion, disorientation, forgetfulness
  • Increase in whining or barking.

At What Ages Does a Dog’s Behaviour Change?

Behavioural changes in our canine pals can occur at different stages such as:

Why my dog’s behaviour changed – Transitioning from Puppyhood to Adolescent Dog

year old behavior change
The rebellious teenage phase of a pup’s life can be challenging for even the most experienced of dog owners.

With the right training, desensitisation, and socialisation, puppies become more confident, calmer, and obedient as they become adults and interact with other dogs and humans. 

Conversely, without the right training and environment, puppies could become aggressive, shy, fearful, or anxious.

Adolescence is also the time when dogs become more independent and start testing boundaries. The adolescent dog’s brain is also less able to regulate emotions and display impulse control. Therefore, owners and trainers need to keep this in mind and adjust their behaviour modification and training plans to suit the adolescent phase.

Unspayed and unneutered dogs may show excessive territory marking, barking, or aggression towards other dogs, as they try to find a mate. Some un-spayed female dogs in heat become excessively clingy with their owners or overly-friendly towards male dogs. 

Un-desexed dogs often become destructive due to sexual frustration. They may have trouble sleeping and may pant or whine excessively. Some refuse food and may even try to run away in the search of a mate. The teenage phase of a dog’s life starts at around 6 months and lasts until 18-24 months of age.

Similarly, female dogs that are on heat, experience behavioural changes associated with an increase in the hormones oestrogen and progesterone. Female dogs can become more vocal, whiny, reactive, clingy and aggressive. A male dog’s behaviour will also change when they sense a female dog on heat, they can go off their food, bark, whine and escape. They experience extreme frustration and will attempt to reach the female dog at all costs.

Why my dog’s behaviour changed – Adult to Senior Dog

change in dog behavior clingy
Older dogs can show aggressive behaviour toward young, energetic puppies. Owners should ensure that older dogs have a quiet space to get away from the high energy of younger dogs.

As mentioned above, owners can find themselves asking “why my dog’s behaviour changed”, when a dog transitions into its golden years. It may show changes in appetite, sleeping patterns, and cognition. Some dogs become forgetful, confused, or irritable due to failing senses, age-related aches pains, and health problems.

FAQ: why my dog’s behaviour changed

Why has my dog’s behaviour suddenly changed?

A sudden change in a dog’s behaviour can indicate that they are feeling chronically unwell or experiencing some sort of pain. Behaviours such as lip licking, growling, biting, increased reactivity or excessive panting should be investigated by a veterinarian. Similarly, a change in routine such as moving house, rehoming, different foods, and less physical or mental exercise can also cause a sudden change in personality.
Another common cause of a dog’s behaviour changing suddenly can be to do with their age. Dogs go through a rebellious phase during adolescence (6 months to 18-24 months of age). Adolescence is a time of fluctuating hormones and limited ability for impulse control and emotional regulation. Such dogs can regress in their training, not responding to previously learned commands.
Similarly, female dogs on heat can be more reactive, clingy, aggressive and vocal. Male dogs that sense female dogs that are on heat, can also become frustrated, go off their food, and will try to escape in order to reach the female.

Why is my dog reverting back to bad habits?

dog behaviour changes with age

Dogs become more of what they do each day. Bad habits like digging, chewing, barking, jumping up, whinging, leash pulling etc tend to be inherently reinforcing. If your dog has pulled on the leash or jumped on guests in the past and they are given the opportunity to do so again in the future, they will quickly revert back to these bad habits. How do you stop your dog from reverting back to bad habits? Limit the rehearsal of bad habits and train alternate behaviours that are incompatible to the bad behaviour. For example, if your dog is jumping up when guests arrive, keep them in their crate or in another room when guests enter and in a low-distraction environment train them to keep four feet on the ground for attention, rewards or praise.

Why does my dog behave differently?

Dogs can behave differently for a myriad of reasons. Some of these include illness, fear, traumatic experiences and training. The first step to finding out why your dog is behaving differently is to have a veterinary check-up where the dog’s skeletal system is examined, heart, ears and eyes are checked and bloods are taken to check for imbalances. If your dog has been through a traumatic experience, seek the help of a qualified animal behaviourist who will be able to assist in creating a behaviour modification plan for your dog.
Hormones can drastically change a dog’s behaviour. Female dogs on heat experience a surge in progesterone that lasts for 9 weeks once they have ovulated. Therefore an undesexed female dog’s behaviour can change for 9 weeks, every 6 months or so. Similarly, any dogs living with an un-desexed female dog will also sense these hormonal fluctuations and can also become more reactive, vocal, clingy and on edge. Undesexed male dogs are particularly effected by bitches that are on heat.

How do you know if your dog has depression?

dog personality change

Depressed dogs will often be easily irritated, sleepy, lacking in energy, clingy and sometimes anxious. They can also develop abnormal repetitive behaviours such as foot licking, scratching, spinning, chewing, chasing flies etc. Dogs can become depressed due to a chemical imbalance in their brain, dietary imbalance or a sudden change in routine.

Conclusion – Why my dog’s behaviour changed

dog behaviors to watch out for

As seen above, a dog’s behaviour may change due to health issues, changes in routine or environment, aging-related causes, stress, a lack of exercise, and even a lack of training.

If you aren’t sure about the exact cause behind the change in your pet’s behaviour, please consult a canine behaviourist to seek the right diagnosis and treatment. Asking yourself “why my dog’s behaviour changed” is the first step in addressing the behaviour problem you’re having. A qualified dog behaviourist in conjunction with your vet should be able to ascertain the root cause of the sudden behaviour change.

If your dog or puppy is behaving badly, consult a professional Dog Behaviourist, online dog training course or a dog trainer to guide you further.

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Hi! I’m Tres! I’m passionate about dog behaviour and training. My dog training methods are effective for all breeds and goals. I have trained dogs for protection, obedience, manners, loose leash walking, crate training and have solved common behaviour problems such as reactivity, barking, separation anxiety and more. Let’s connect, sign up to my free newsletter (above) for helpful tips and upcoming training events.
dog trainer Sydney

Hi! I’m Tres! I’m passionate about dog behaviour and training. My dog training methods are effective for all breeds and goals. I have trained dogs for protection, obedience, manners, loose leash walking, crate training and have solved common behaviour problems such as reactivity, barking, separation anxiety and more. Let’s connect, sign up to my free newsletter (above) for helpful tips and upcoming training events.
dog trainer Sydney

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