A Texas pet owner has shared heartbreaking footage of her surviving dog mourning the loss of the senior rescue she considered her big sister.

Ziva was so much more than just a pet to owner Lindy Cain from Austin, Texas. "I had Ziva from the age of 15 until I was 30. That's half of my life. She was truly my best friend," Cain told Newsweek.

She first met Ziva as a 3-month-old puppy while volunteering as a foster at her local shelter. "Ziva was found alone in a flower bed in Houston. That's all they knew about her. As soon as I saw her picture, I knew she was going to be mine," Cain said. "She had this silky black fur, big brown eyes, and short little legs."

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She added that Ziva quickly became an indispensable part of her family and early adult life. "She was incredibly attuned to people from a young age, and her favorite thing to do was just sit quietly next to her favorite humans," Cain said.

Her pain at losing such a beloved pet after such a long time together is understandable, but Cain has not been alone in grieving for Ziva.

Two and a half years ago, Cain added another dog to her pack: Lola. Unlike Ziva, this pup came from a breeder and, as a nervous 6-month-old puppy, took a little longer to adjust to her new life.

But her big sister Ziva was there for her every step of the way. "She was fearful at first but looked up to Ziva," Cain said. "She would do something if Ziva did it."

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For a time, they were happy together but then Ziva became unwell. "She was diagnosed with terminal nasal cancer," Cain said. "We did chemotherapy and everything to extend her life for as long as we could."

Eventually, however, Cain could see that Ziva's body was failing her, and it was time for her to cross the rainbow bridge. It has been a little while since Ziva's passing, but Cain gets the feeling that Lola is still coming to terms with what happened.

"After Ziva passed, we brought home Ziva's collar and let Lola sniff it," Cain said. "Ziva passed nine months ago and, to this day, Lola will climb from the couch to the table where Ziva's ashes and collar are to sniff them."

While the loss of a dog is difficult to take for most humans, research suggests surviving canines experience a similar period of mourning after the death of a fellow pet.

In 2022, a study published in the journal Scientific Reports saw 426 adults who had owned at least two dogs, one of whom died, surveyed on the topic of how their surviving canines reacted to the loss.

A variety of negative behavioral changes were commonly reported. Attention-seeking increased (67 percent); the majority of surviving dogs appeared to play less (57 percent); while a significant number were less active (46 percent); and many slept more (35 percent).

Some even reported witnessing an increase in fearfulness among surviving dogs (35 percent), while many ate less (32 percent) while vocalization also increased (30 percent) in a significant proportion of the pups involved in the research.

Cain saw firsthand how the death of a fellow dog can affect the pet left behind. "Lola wasn't herself after Ziva passed. She had a sadness to her and wanted more cuddles from me," Cain said. "She lost her confidence and would look around like she was looking for Ziva when we went on walks."

Eager to provide Lola with a much-needed boost during this difficult time, Cain did the only thing that made sense. "Lola needed another dog in the home to feel secure, so we quickly got her a puppy," she said. "I think it helped her move on from losing her best friend Ziva."

Cain's new puppy can never replace the dog who was her "best friend" and a big sister to Lola, the energy and excitement of the new arrival has helped lift the gloom. Ziva now lives on, not in the memories of her final few months, but in the happy moments they shared together in all the years prior.