The author does not lay out their definition of nurturing explicitly. The most complete definition I can derive from the article is that nurturing is engaged caregiving marked by responsiveness and physical closeness that is supported by hormonal changes in the caregiver.
They have nothing to say about nursing other than that it involves oxytocin release (presumably an instance of nurturing).
In your short comment, you didn't make any attempt at determination beyond saying the names "nurturing and protection" and "birthing and nursing". OK, so what is the distinction? Are you claiming that birthing and nursing are mechanical acts that secure existence of the organism, but fail to secure some other thing that is called nurturing and protection? Or are birthing and nursing mere instances of a homogenous nurturing and a homogenous protection, and so one's quota for nurturing and protection are filled in the same way experience points fill up in a video game?
So it's the opposite: your OP and I are the only ones here making a concrete distinction between nursing and nurturing (although your OP didn't really say much, either).
Like I said, Donald Winnicott explores this question at length. Unfortunately he is not a good Marxist who historicizes these categories; he works squarely in post-war British society and so obviously has his limits. But he has the courage to criticize the emptiness of medical empiricism and the fear of determinateness of people like the article's author.
Here's Winnicott in The Child, the Family, and the Outside World:
> The infant who has had a thousand goes at the breast is evidently in a very different condition from the infant who has been fed an equal number of times by the bottle; the survival of the mother is more of a miracle in the first case than in the second. I am not suggesting that there is nothing that the mother who is feeding by bottle can do to meet the situation. Undoubtedly she gets played with by her infant, and she gets the playful bite, and it can be seen that when things are going well the infant almost feels the same as if there is breast feeding. Nevertheless there is a difference. In psychoanalysis, where there is time for a gathering together of all the early roots of the full-blown sexual experience of adults, the analyst gets very good evidence that in a satisfactory breast feed the actual fact of taking from part of the mother’s body provides a ‘blue-print’ for all types of experience in which instinct is involved.
Personally, this aligns with my own observations of my daughter. The sensuous conflict of breastfeeding is a negotiation of the psychic and physical line between self and other where everything is at stake and desires are understood and worked out at the level of the skin. It's practically impossible to make a bottle (or anyone/anything else!) fulfill this function.
Anyway, Winnicott goes on in great detail for chapters. Also relevant is a draft of a talk he gave titled This Feminism, which is probably more relevant to the underlying tensions in these comments:
> This is the most dangerous thing I have done in recent years. Naturally, I would not have actually chosen this title, but I am quite willing to take whatever risks are involved and to go ahead with the making of a personal statement. May I take it for granted that man and woman are not exactly the same as each other, and that each male has a female component, and each female has a male component? I must have some basis for building a description of the similarities and differences that exist between the sexes. I have left room here for an alternative lecture should I find that this audience does not agree to my making any such basic assumption. I pause, in case you claim that there are no differences.
Again, he's unfortunately not interested in how psychic development might be a historically limited category; he naturalizes "nurturing" (he doesn't use this word often, actually), but at least he acknowledges the concrete limitations of mother and fathers (and all the other characters) as they actually exist. And he does this without ever invoking the name of a hormone once.