This is a significantly underappreciated piece of the decline in white birthrates. Other pieces are obviously race mixing (supported by brainwashing and mass non-white immigration), belief that having kids is unethical because of climate change (also the result of brainwashing), delaying starting a family until it's too late (for various reasons, mostly career-oriented or the need to slut it up for two decades before settling down), and others.
Those aforementioned pieces of the white birthrate problem are well appreciated and receive their share of attention. The dog piece does not. The mechanism for how it lowers white birth rates is this:
A woman of breeding age gets a dog. The dog is a financial drain on her ($1k a year at minimum), which exacerbates the financial anxiety of starting a family. It's also a drain on social time that would otherwise be used to meet future husbands—she can't be out long because she can't leave the dog alone, and she's tired because she has to get up early to walk it. And the most critical mechanism is that the dog becomes the object of her maternal instincts. She says it herself: