"How is Corrina handling the new arrival?" is often the first question I am asked since my daughter Lydia's birth six months ago. Predictably, it's the inquiry before how I'm doing, or how my husband is doing. But sometimes it even comes before: "How is the baby sleeping?"

This may be in part because Corrina is a force unto herself and to those who've known her since we first brought her home from her foster family, she's still that manic whirl: now here, now there, now up, and rarely down. But they also ask because Corrina is especially sweet, conveying somehow in the tumult of her crazed efforts to gain attention a depth of silly soulfulness that draws people into relationship with her.

Corrina is the dog I've wanted since I was a girl. She's a gorgeous black Labrador Retriever who welcomes affection. She is loyal and protective, funny and playful. She was probably a year old when she first came home with us two years ago, but "labs" are puppies for a long time and she's still more puppy than dog. She's also a highly bred hunting dog, according to a breeder we met after we adopted her, her origins otherwise lost to us. But we don't hunt, and I suspect she suffers for this. She's a coiled spring of a dog bred to run, find, and retrieve in muddy bogs and marshes. As an urban dweller, she's forced to be content with occasional trips to the river, or, considerably more tame, walks, when on a really great day she might find a mud puddle to roll in.

I am not Corrina's mama—but I'm the closest thing she's got. By making sure she gets the singular pleasure of a game of fetch or long walk each day, I can keep her happy and mellow and tell her a thousand belly rubs' worth that she is known and loved: the work of a mama.

I have learned things about mama-ing through helping Corrina transform from a wild blur of fur to an animal recognizable as a pet, often, even a good pet. I've learned, for example, how to recognize when the moment to correct misbehavior has gotten by me and left me only the dishonorable option of traumatizing a creature who will not understand my anger or the frustrating one of accepting that living with an untrained dog means I can't leave my favorite shoes out in the living room overnight. Corrina has taught me to give up insisting on how things should be, and to see how they are—to fall in love with her as she is, not as a preconceived ideal. This is surely the heart of mamahood.

Nonetheless, it has become plain as day: Corrina is not my baby. She is just a dog.

Long ago I was visiting a friend who had recently had a baby. She was a cat person. She had two cats when her son was born, both of which were the flamboyant and compelling protagonists of many funny stories she told at parties. Shortly after her son was born, she caught them stalking him in his crib. "I never thought I'd say this," she told me. "But that's when I knew: they're just cats." Heartbroken, she resolutely found new homes for them immediately following the incident. Some will say that only proves she wasn't a true cat person. I'd say it proves she'd become a mama.

When my husband and I adopted Corrina, we were purposeful in limiting our perceptions of ourselves as "Dad" and "Mom." For her sake as well as ours, we deliberately set out to treat her and love her as a dog rather than as the surrogate child that pets of childless people can become. We hoped that as a result, there'd be less disruption for her, and for us, when or if real children came along.

I'd probably still recommend it as a strategy, but even good execution reveals its limits. There was no way to prevent Corrina from suffering a loss of attention and loyalty with the arrival of our daughter. Corrina used to sleep at the foot of our bed, get two long walks a day, a long bout of play in the evening and at least one extended belly rub. And that was just the weekday regimen. On the weekends, she was almost certain to get a few games of fetch, and sometimes even more than one trip to the river.

We still try to make sure Corrina gets a least one daily walk, but in these first six months of Lydia's life, Corrina's games of fetch have been rare and trips to the river a distant memory. Some days, caring for Lydia is all I can do. I forget to eat and drink. I'm lucky if I manage to shower before bed. On such days, the only attention Corrina may get is several brusque orders to move out from underfoot or to "come inside or stay out." She gets fewer belly rubs, because to rub her belly properly is to coat my fingers in grime—the same fingers Lydia sucks and chews. And adding insult to injury, we've moved her dog bed to the foot of Lydia's crib so Lydia doesn't have to sleep alone (which also means Corrina's sleep is as disturbed as ours).

I've traded in my hat as the proud proclaimer of Corrina's safety and friendliness, and am newly watchful and wary of her. At the same time I delight in the moments when Lydia and Corrina interact, I am on heightened alert, hair-trigger ready to correct Corrina for any rough gesture. Though I still believe she would never intentionally hurt a person, I am not sure if she recognizes Lydia as a person yet. Even more to the point, I know better than to trust her to know what causes harm, having worn raised red stripes across my face from her paws striking out in play, and a sore bloody tongue caught between my teeth during one of her affectionate head butts.

I watch Corrina wince when Lydia reaches for her, and I feel equal parts compassion and nervous concern, wondering whether Corrina minds Lydia's rough exuberant grabbing and pulling. Does it mean that one day she'll snap and understandably chastise Lydia with an inadvertently too-powerful nip? What choice would we have but to find a new home for Corrina if she bit Lydia?

Much as I try, I'll never love Corrina as unreservedly as I once did; now, Lydia will always come first.

Ironically, in five years, Lydia will be Corrina's best friend, as Corrina will be hers. Corrina is likely to enjoy the exalted status of being Lydia's first and favorite confidante—allowing Lydia to return multi-fold the level of attention and affection she diverts from Corrina today. Furthermore, there's little doubt that Lydia will be Corrina's new mouthpiece, regularly begging to go to the park or river to play.

Now, Corrina flinches at Lydia's failures to "touch gently," but she also comes back almost immediately, submitting to more of her youngest and most ardent fan's battery. And, every time Corrina patiently offers herself again, my heart overflows with love for her. It's sweet that Lydia loves Corrina, but Corrina's loving Lydia moves me more deeply. Maybe it is tolerance more than love, but it reveals development in their growing bond—and the beginning of Lydia's experience of the intimate unconditional friendship of a dog. I want that experience for my daughter.

Then Corrina will know a child's filial devotion, that specific type of innocent adoration for which dogs uniquely qualify among their animal kin. And I want that for my first baby.

Phoebe Varinia DeMund is a stay-away-from-the-office mama living in Sacramento. She's a writer, citizen activist, and her new daughter's delighted mother. She lives with her husband, daughter, and dog.