In 1948, my maternal grandparents, Florian and Lucille Yeaton, brought home Bonnie, the runt of a border collie litter purchased in Farmington. This scrappy pup caught Grampa’s attention by fearlessly wrestling with littermates twice her size.

They took her to their Mercer farmhouse, where she slept on a horsehair blanket behind the wood cookstove. However, their hopes for a collie to herd sheep and dairy cows dimmed as Bonnie’s weight plummeted.

As a last resort, Grammy Lue wrapped Bonnie in the blanket and, in a gamble, placed her in the pigpen with a 250-pound sow nursing six piglets.

“We’ll know by day’s end whether the sow takes to her,” Grammy said to Grampa.

For 10 days, Bonnie nursed alongside the pink piglets, thriving under her unlikely foster mother’s warmth and care. Her weight — scarcely three pounds — more than doubled. Within two months, she was racing between the farmhouse and the barn.

My grandparents initially wondered if such an unusual start would leave a lasting mark. It did, but not the one they feared. Bonnie matured into an extraordinarily intelligent working dog, consistently proving her capabilities in protecting her family and livestock.

One summer afternoon in 1953, my 5-year-old brother, Robert, came face-to-face with a rabid fox behind the barn. Bonnie didn’t attack. Instead, she steadily nipped at Robert’s heels, driving him back toward the farmhouse while keeping her body between him and the fox. Grampa killed the fox with his shotgun.

A year later, Robert and our cousin, Cheryl, accidentally started a barn fire while playing with matches. Bonnie’s frantic barking alerted the family before anyone smelled smoke. Grampa fought the flames with pails of rainwater from the cistern, Mother smothered them with wet blankets, and Grammy herded the frightened livestock into the pasture. Together, they saved the barn.

But Bonnie’s greatest feat occurred on a sweltering August day in 1958.

While wading in the Sandy River to cool off, my 6-year-old twin brother, Don, was swept into the deep channel. Mother dove in after him but couldn’t dog-paddle fast enough to close the gap as he drifted downstream.

Bonnie understood the river’s currents better than either of them. Instead of immediately jumping in, she sprinted along the high bank, tracking Don as he fought to keep his head above water. Nearly 300 feet downriver, she launched off the bank, entered the current just ahead of the hairpin rapids, clamped onto his shirt collar, and hauled him onto a gravel bar.

The next morning, Don, still shaken, sat beside Grampa in the milking parlor. From his three-legged stool, Grampa squirted warm milk to the waiting barn cats and Bonnie, as he did every morning. Watching Bonnie lick her whiskers, my twin laughed through his tears and pulled her close.

The day before, she had saved his life — that morning, she helped restore his spirit.

Age never dulled her instincts. Shortly after midnight in October 1961, Don and I woke to growls rising from the pumpkin pine floorboards at the foot of our bed.

“Why’s Bonnie growling?” we yelled into the dark.

“Might be a bear in the barnyard,” Grampa answered from the adjacent bedroom. “She found fresh tracks in the orchard yesterday.”

He lit a kerosene lantern and retrieved the 12-gauge from above the kitchen door. Bonnie paced and whined at the latch. The second it lifted, she shot through the doorway and bolted toward the pigpen, her dark silhouette framed by a huge harvest moon.

“You boys go back to bed,” Grammy barked.

We obeyed but opened our bedroom window to listen. The hogs were squealing, Bonnie was barking, and a single shotgun blast cracked across the farm. Then everything went deadly quiet.

The next 10 minutes felt like an hour before Grampa and Bonnie returned to the kitchen.

“She chased a bear clean out of the pigpen,” he said, still catching his breath. “The pen door’s stove to hell, but the hogs are fine.”

Two nights later, a few miles from our farm, Ralph True shot the same bear after it killed one of his sheep. The boar weighed 490 pounds.

“Its front paws,” he told Grampa, “were the size of dinner plates.”

When cancer took Bonnie in April 1962, Grampa wrapped her one last time in the ratty horsehair blanket she’d slept on her entire life and carried her up the knoll to the apple orchard — her favorite spot on the farm. He dug her grave that night by moonlight, working past the frost line with a pickaxe and shovel. The next afternoon, my three siblings and I picked yellow daffodils from the south side of the farmhouse and planted them on her grave.

That evening, my heartbroken 5-year-old sister, Gale, barely ate her supper. When the meal was over, she quietly walked behind the cookstove and scraped her plate into Bonnie’s enamel bowl.

In the morning, her eyes lit up at the sight of an empty bowl.

Years later, E.B. White gave me the words for what Bonnie meant to our family: “A really companionable and indispensable dog is an accident of nature. You can’t get it by breeding for it, and you can’t buy it with money.”

Ron Joseph of Sidney is the author of “Bald Eagles, Bear Cubs, and Hermit Bill: Memories of a Maine Wildlife Biologist,” published by Islandport Press.