A pet’s loyalty is one of the most compelling reasons to get a pet in the first place. Without a doubt, you would not love your dog or cat as much if it would betray you by biting or clawing you. That being said, there exist other loyal pets aside from cats and dogs. But one step at a time…
The Most Loyal Pet of Them all: The Dog

If a dog accepts you as the alpha of the pack, a dog’s loyalty can be seemingly endless. This faithful companion will protect you from hostile people or other animals, will alert you of danger (eg. a burglary in your home) and will try to help you in any which way it can, even it means peril for itself.
There have been cases in which abandoned dogs or otherwise separated dogs have been able to reunite with their owners after traveling for hundreds or even thousands of miles. And believe me, it’s not because they couldn’t find food otherwise.
Why are Dogs Loyal?

In essence, it all comes down to basic instincts (pack animal behavior) and selective breeding of those individuals that display desirable traits.
Scientists believe that the earliest bond between humans and wolves was formed about 14,000 years ago (National Geographic). Our ancestors noticed that wolf pubs, when raised by humans, were less aggressive towards their adoptive parents. when compared to their wild siblings Moreover, they were helpful during a hunt by rousting or sniffing out prey.
Initially, the most sought after qualities were tameness, loyalty, and the ability to help during a hunt . Only much later in our history, other features such as a certain look or size became more important and the differentiation into all the known dog breeds developed.
If loyalty is for you the most important aspect of having a pet, look no further and get a dog. There is nothing that comes close in the animal kingdom. However, becoming the Alpha to your dog can be tricky. Here is what it takes.
A Distant Second in Pet Loyalty: The Cat

Although domesticated before dogs, cats are not as loyal as dogs. Reasons can be found in the natural behavior of their wild counterparts. Wolves live in packs to maximize their hunting success and overall chances of survival. Wild cats on the other hand are typically loners and hunt by themselves.
This makes them overall more independent and less reliant on their care takers. Still, cats will show you tons of affection, albeit only when they want to, on their own terms.
Overall, their love is more conditional. As a matter of fact, cats seem to have the ability to put the pet-owner hierarchy on its head by punishing the owner if the provided food is not good enough.
Btw, click here if you want to know if you can walk a cat on a leash.
Everything else: Horses, Birds, Ducks, Rodents, etc.

Other than dogs and cats, there isn’t really another species that has been domesticated to be a loyal pet. Horses might be the only exception, but they were bread for transportation and field work, not as loyal pet animals.
Still, a horse can be very tuned to its owner and show signs of loyalty. This is most likely because wild horses live, not unlike wolves, in a herd community. But would a horse go to great length to save its owner from danger? Probably not…Also, horses have, because of their sheer size, poor bedside manners 🙂
As far as ducks, rodents, and birds go, although they may make great pets otherwise, I wouldn’t characterize their behavior as loyal. It is mostly food-driven and your beloved parrot or pet rat would choose their freedom the moment you give them the chance.