• Thinkstock
    1 of 5

    By Justine Lee

    A Golden Retriever and a Maltese may seem like an odd couple, but Indy and Katie were as close as two dogs could be.

    RELATED: 3 Pet Symptoms You Should Never Ignore

    After spending their days together, Katie would sleep on Indy's back each night, her four-pound body rising and falling with his snores.

    "It was adorable," says their owner, Karen Wolkenberg of Roslyn, NY. But at fourteen years old, Indy's health deteriorated, and the family had to put him to sleep. Immediately after, the normally sweet-natured Katie, who at age ten had grown up with Indy, turned nasty, refusing to eat and urinating all over the house.

    "I'd look at her and think, What's going on?" Wolkenberg says. "Then it finally hit me that she was grieving."

  • Thinkstock
    2 of 5

    Losing a pet is always difficult for an owner (here's how you should best mourn the loss of a pet), but it can be equally hard on the household's canine companions.

    Dogs in particular feel the loss of a fellow pet, as they are pack animals who enjoy being surrounded by friends. In fact, a study from the ASPCA found that two-thirds of dogs show recognizable signs of grieving, such as a decrease in appetite, clinginess, and lethargy. I've also found that some dogs whine and bark more or sleep in unusual places -- this type of attention-seeking behavior may happen because the dog has pent-up "play energy" that he's not able to release with a friend.

    "The good news is that in most cases, these changes resolve in a couple of weeks," says Stephen Zawistowski, PhD, an author on the ASPCA study.

  • Thinkstock
    3 of 5

    One key way to help your dog recover is by spending time together: Take longer walks, cuddle more, or devote an extra twenty minutes to throw around a tennis ball. If your pet won't eat, don't tempt her with human comfort food like pizza or ice cream.

    RELATED: Add Years to Your Pet's Life

    Instead, stoke her appetite by minimizing stress (no houseguests or changes to her territory) and offering doggy treats. You can leave the former dog's bed and toys for consistency during the transition, but remove the bowl so she doesn't feel a sense of competition for food. Try taking your dog to a dog park. If she looks like she wants to play, schedule some doggy playdates. But if she stays away from other animals, then respect her need for alone time.

    And even if she's mopey, encourage her to take short walks. I also tell my patients' owners that it's fine to invite an extra clingy dog to share their bed.

  • Thinkstock
    4 of 5

    Animals are sensitive to human emotions, so try to minimize extravagant displays of grief in front of your dog. If you're tempted to replace the pet that died, hold off. I advise waiting two or three months to make new additions, in order to give the dog (and you!) time to adjust. Your pooch is accustomed to his former companion, so introducing an attention-seeking, hyperactive puppy can be physically and emotionally stressful. Even an older, more mellow dog might be taxing, as your pet will feel the need to fight for turf and pecking order.

  • Thinkstock
    5 of 5
    Next: 10 Heartbreaking Animal Mourning Rituals

    No one knows how long a dog's memory is, but based on anecdotal evidence, I believe dogs do remember companions for some time. That said, while the process may take a few weeks or even months, almost all of my patients' owners notice a return to normal activity.

    If grieving signs last longer, bring your pet to the vet to rule out underlying medical problems, the timing of which could be coincidental.