Getting a Second Dog: When It Works and When It Doesn’t

In brief

A second dog can enrich life for both people and dogs. It isn’t a remedy for every problem, though. Four things matter. First: a second dog is not a reliable remedy for problems with being left alone; in a video study, dogs in multi-dog homes were actually more active when left alone. Second: conflict between dogs in the same home isn’t the rule, but it happens; in a UK survey, 8 percent of owners reported it. Third: in clinical case series on serious conflict, same-sex pairs were overrepresented, and the aggressor was often the younger dog and the later arrival. Fourth: resources such as food, chews and resting places were the most common trigger in the largest case series.

This guide shows which questions to ask yourself before deciding, what the studies on conflict in multi-dog homes say, which combinations tend to work, and how to plan the move-in.

1. The honest question first: why a second dog?

1.1 So the dog isn’t alone?

This is one of the most common reasons, and it carries less weight than many people hope. Stephan, Leidhold and Hammerschmidt (2021) video-recorded 77 dogs while they were home alone as part of their normal routine, 32 from single-dog homes and 45 from multi-dog homes. Most dogs were calm. Dogs in multi-dog homes, however, showed more physical activity, especially in the first hours after their owners left, and males in multi-dog homes were more vocal. Whining was not reduced by the presence of familiar dogs.

Two further studies point in a similar direction. In a test with 22 cohabiting dog pairs, dogs showed fewer signs of stress when their familiar housemate was present than when completely alone. An unfamiliar person, however, had a stronger calming effect than the familiar dog (Mariti et al., 2014). In an older study of laboratory-housed dogs, a familiar caretaker reduced the stress response to a new environment, whereas a familiar kennel mate did not (Tuber et al., 1996).

In practice, this means a dog with real separation problems needs training and, where appropriate, veterinary help. A second dog may be pleasant company for some dogs, but it doesn’t replace that. In the worst case, you end up with two dogs that can’t be left alone.

👉 Separation anxiety in dogs

👉 Social referencing and social buffering in dogs

1.2 Because the first dog needs company?

Some dogs greatly enjoy the company of other dogs; others do better with selected dog contacts outside than with a housemate who is always there. Whether your dog likes being with other dogs isn’t shown at the dog park but by how he behaves during longer, calm encounters, for example when a familiar dog comes to visit.

👉 Social contact for dogs

1.3 What a second dog costs

In practice: a second dog doesn’t just double food and veterinary costs, insurance and license fees. In the early period, he also needs individual training, individual walks and his own attention. Walking two dogs on leash at the same time, traveling with both or finding care for two is considerably more work. If you’re already at the limit of your time with one dog, it won’t get easier with two.

👉 Before getting a dog

2. How often do dogs in the same home fight?

In a UK owner survey, 8 percent of owners reported aggression toward another dog in the same home, meaning barking, lunging, growling or biting. Toward unfamiliar dogs, the figure was 22 percent. Aggression toward dogs and toward people rarely occurred together (Casey et al., 2013). In this UK owner survey, 92 percent reported no aggression toward another dog in the same household.

In the same survey, aggression toward dogs in the household was associated with increasing age of the dog and with the use of punishment or negative reinforcement in training. The factors studied, however, explained less than 15 percent of the differences overall. Whether punishment contributes to conflict or owners turn to punishment because of it can’t be determined from such a survey (Casey et al., 2013).

When serious conflict does occur, it can be severe. In a case series of 38 dog pairs referred to a behavior clinic for fighting at home, dogs needed veterinary treatment in 15 of 30 cases with injury information, and in 3 cases owners who had intervened needed medical attention (Wrubel et al., 2011).

👉 Multi-dog households

3. Which dogs suit each other?

3.1 Sex

In clinical case series on fighting at home, same-sex pairs were overrepresented, especially pairs of two females (Sherman et al., 1996; Wrubel et al., 2011). In the largest analysis, of 305 dog pairs from a behavior clinic, 61.6 percent of pairs were same-sex, and 70 percent included at least one female (Feltes et al., 2020). Observations in a group of dogs show the same from the other side: mixed-sex pairs were more often friendly toward each other than same-sex pairs (Trisko & Smuts, 2015).

The authors of the large case series therefore advise against same-sex pairs (Feltes et al., 2020). That recommendation goes further than the data support, however: these were dogs referred for problems, and no study has followed newly formed pairs over time. Clinical case series suggest that same-sex pairs are more common among severe conflict cases. They do not allow the absolute risk of a newly formed same-sex pair to be calculated, and many same-sex pairs live together without problems.

3.2 Age and order of arrival

In the case series, the aggressor was often the younger dog and the later arrival (Wrubel et al., 2011). In the large analysis, the aggressor had joined the home after the dog it attacked in 59.3 percent of pairs. On average, it was 16 months younger and 1.5 kilograms heavier (Feltes et al., 2020).

In practice, conflict can also become visible only as the younger dog reaches social maturity. The cited case series did not study this course prospectively, however. So plan not just for the first weeks but also for the young dog’s later development.

3.3 Size

In a study from South Africa on bite injuries caused by dogs from the same household, the injured dog was larger than the other dog in only 10 percent of 89 pairs with size information; in 42 percent both were about the same size, and in the remaining pairs the injured dog was smaller (Hanekom et al., 2025). This shows that smaller dogs were much more common than larger dogs among the injured animals, but it does not establish that smaller dogs generally suffer more severe injuries. These figures apply to the clinical population studied there. A clear size difference isn’t a reason to rule a pairing out, but it calls for more care during play and in everyday life.

3.4 Your first dog

Take an honest look at your first dog before deciding. In a large owner survey, dogs in multi-dog homes more often showed resource guarding toward other dogs, avoidance and rapid eating than dogs without other dogs in the home (Jacobs et al., 2018). In practice, these points also matter:

• Health and age. An older dog with pain or declining senses can’t easily get out of the way of a young, boisterous dog. Have him examined by a veterinarian first.
• Social behavior with other dogs. How does he behave when a familiar dog visits your home for a longer time?
• Does he guard resources from other dogs, such as food, chews, resting places or you?
• Is his training solid? A second dog tends to pick up habits and arousal rather than cues.

👉 Resource guarding in dogs

4. Meeting and moving in

There is no study comparing different ways of introducing two dogs. The following steps are one possible practical approach from training.

4.1 Before the move-in

In practice: let both dogs meet several times on neutral ground beforehand, ideally on walks side by side at a distance that gradually decreases. Watch whether both relax, whether they give each other space and whether one constantly crowds the other.

4.2 The first weeks

In practice: set up your home so that competition doesn’t arise in the first place.

• Feed separately, ideally in different rooms or separated by a gate.
• Give chews and special toys only separately and put them away afterward.
• Separate retreats for each dog where he won’t be disturbed.
• Defuse narrow spots. Hallways, doors and stairs are typical places for bumping, especially when excited.
• Keep exciting moments calm. Greetings, food preparation and visitors are high-arousal situations.
• One-on-one time for each dog, with his own training and his own walks.
• Separate them when unsupervised until you’re sure both are relaxed with each other.

In the case series of 38 pairs, 14 of 25 responding households named the presence of a family member as a trigger for fights (Wrubel et al., 2011). The study didn’t establish why. It is, however, a reason to keep an eye on your own closeness and attention as a possible resource.

👉 Puppy training weeks 1–2

5. Warning signs and when you need help

In the large case series, resource guarding was the most common trigger for fights, at 72.8 percent (Feltes et al., 2020). Three features were associated there with a poor outcome, meaning permanent separation, rehoming or euthanasia: same-sex pairs, bites that broke the skin, and aggression at the mere sight of the other dog rather than only in contested situations.

In practice: take these signs seriously:

• One dog constantly blocks the other, for example at doors, at the resting place or near you.
• One dog repeatedly stares at, freezes over or growls at the other.
• One dog avoids certain rooms, no longer eats in peace or withdraws.
• Altercations become more frequent, longer or more intense.

Get professional help early, at the latest after bites with injury, with attacks at the mere sight of the other dog or if you can no longer separate the dogs safely. Don’t reach in with your hands during a fight. Until you get help, keep both consistently separated whenever nobody is supervising.

👉 Warning signals in dogs

👉 Dog trainer or behavior consultant?

6. A note on the evidence

The evidence on which second dog suits which first dog is thin. No study has followed newly formed pairs over time. The findings on sex, age and order of arrival come from case series of dogs referred to behavior clinics for fighting (Sherman et al., 1996; Wrubel et al., 2011; Feltes et al., 2020). They show how these cases were composed, not how high the risk is for a particular pair. The largest analysis is based on clinic records reviewed retrospectively. The figures on size differences come from a South African clinical population (Hanekom et al., 2025).

The surveys (Casey et al., 2013; Jacobs et al., 2018) show associations at one point in time, not causes. The studies on being left alone include 77 dogs (Stephan et al., 2021), 22 dog pairs (Mariti et al., 2014) and laboratory-housed dogs (Tuber et al., 1996). The steps for meeting and moving in in this guide are marked as practical experience.

7. Conclusion

A second dog can work well if you really want one, and not as a solution to a problem your first dog has. In the UK owner survey, the large majority reported no aggression toward another dog in the same household. In clinical conflict cases, resources play a very frequent role; separate feeding, controlled chews and clear retreat areas can prevent many predictable conflict situations.

The three things that make the difference:

Decide honestly. A second dog is not a remedy for separation problems and needs time of its own.

Choose carefully. Assess your first dog honestly and weigh sex, age and size deliberately.

Manage resources. Feed separately, provide separate retreats, give chews only separately and defuse narrow spots.

Key takeaways on getting a second dog

Not a reliable remedy for being alone. Dogs in multi-dog homes were more active when left alone, and whining was not reduced by familiar dogs (Stephan et al., 2021).

A person calmed more than a familiar dog. An unfamiliar person had a stronger calming effect than the familiar housemate (Mariti et al., 2014).

Fighting at home isn’t the rule. 8 percent of owners reported aggression toward a dog in the same home, 22 percent toward unfamiliar dogs (Casey et al., 2013).

Same-sex pairs are overrepresented in case series. 61.6 percent of 305 clinic pairs were same-sex (Feltes et al., 2020).

The younger, newer dog often attacks. In 59.3 percent of pairs, the aggressor had joined later and was on average 16 months younger (Feltes et al., 2020).

Resources are the most common trigger. Resource guarding was the trigger in 72.8 percent of pairs (Feltes et al., 2020).

Three features of a poor outcome. Same-sex pairs, bites that broke the skin and aggression at the mere sight of the other dog (Feltes et al., 2020).

References

• Casey, R. A., Loftus, B., Bolster, C., Richards, G. J., & Blackwell, E. J. (2013). Inter-dog aggression in a UK owner survey: Prevalence, co-occurrence in different contexts and risk factors. Veterinary Record, 172(5), 127. https://doi.org/10.1136/vr.100997
• Feltes, E. S. M., Stull, J. W., Herron, M. E., & Haug, L. I. (2020). Characteristics of intrahousehold interdog aggression and dog and pair factors associated with a poor outcome. Journal of the American Veterinary Medical Association, 256(3), 349–361. https://doi.org/10.2460/javma.256.3.349
• Hanekom, J., Thompson, P. N., Schoeman, J. P., & Van Vollenhoven, E. (2025). Household hostilities: A descriptive study of inter-dog aggression requiring veterinary treatment of dog bite wounds in Pretoria, South Africa. Applied Animal Behaviour Science, 292, Article 106819. https://doi.org/10.1016/j.applanim.2025.106819
• Jacobs, J. A., Coe, J. B., Pearl, D. L., Widowski, T. M., & Niel, L. (2018). Factors associated with canine resource guarding behaviour in the presence of dogs: A cross-sectional survey of dog owners. Preventive Veterinary Medicine, 161, 134–142. https://doi.org/10.1016/j.prevetmed.2017.02.004
• Mariti, C., Carlone, B., Ricci, E., Sighieri, C., & Gazzano, A. (2014). Intraspecific attachment in adult domestic dogs (Canis familiaris): Preliminary results. Applied Animal Behaviour Science, 152, 64–72. https://doi.org/10.1016/j.applanim.2013.12.002
• Sherman, C. K., Reisner, I. R., Taliaferro, L. A., & Houpt, K. A. (1996). Characteristics, treatment, and outcome of 99 cases of aggression between dogs. Applied Animal Behaviour Science, 47(1–2), 91–108. https://doi.org/10.1016/0168-1591(95)01013-0
• Stephan, G., Leidhold, J., & Hammerschmidt, K. (2021). Pet dogs home alone: A video-based study. Applied Animal Behaviour Science, 244, Article 105463. https://doi.org/10.1016/j.applanim.2021.105463
• Trisko, R. K., & Smuts, B. B. (2015). Dominance relationships in a group of domestic dogs (Canis lupus familiaris). Behaviour, 152(5), 677–704. https://doi.org/10.1163/1568539X-00003249
• Tuber, D. S., Hennessy, M. B., Sanders, S., & Miller, J. A. (1996). Behavioral and glucocorticoid responses of adult domestic dogs (Canis familiaris) to companionship and social separation. Journal of Comparative Psychology, 110(1), 103–108. https://doi.org/10.1037/0735-7036.110.1.103
• Wrubel, K. M., Moon-Fanelli, A. A., Maranda, L. S., & Dodman, N. H. (2011). Interdog household aggression: 38 cases (2006–2007). Journal of the American Veterinary Medical Association, 238(6), 731–740. https://doi.org/10.2460/javma.238.6.731

Note: This guide does not replace individual advice. If your dogs bite each other seriously or one dog attacks the other at the mere sight of it, keep them consistently separated and get professional help.

Frequently asked questions about getting a second dog

Decision, choice and living together