The cow is not your mother. She doesn’t give you milk; you take her milk (which wasn’t meant for you) away from her forcibly. Although buffaloes do precisely the same job that cows do, and supply a good chunk of the milk consumed by Indians, for some reason, nobody seems to be claiming descent from them. If providing nutrients is the criterion for motherhood, all edible plants, and animals yielding milk, meat, honey, etc., should be your mothers. If it is not nutrients in general, but milk in particular, any mammal should be eligible to be your mother.
Is confinement to a shed or a mostly dirty circumscribed area; access to garbage as food; extraction of heavy physical labour; administration of loads of antibiotics (therapeutic or prophylactic); crossing with quite possibly immoral studs, or cutting out the work of the studs altogether, and artificially inseminating repeatedly to stack one pregnancy on another the way to treat mothers? On deeper reflection, maybe this is why people call cows their mothers, confessing in this roundabout way that they mistreat their human associates, or at least treat them as cash cows. Also, 'bovine' is not a complimentary adjective: Try calling a human mother a cow.
People who do not eat meat may be going into contortions patting themselves on their backs for their animal-friendly ethos, but killing is not the only cruelty. Daily milking (by anything other than the calf’s mouth); robbing colostrum, honey, etc.; shearing; confining animals to cages, sheds, or dirty, narrow streets; and making them slog pulling loads, all involve inconvenience at best, and torture at worst, of the animals in question. And animal-rearing, particularly cattle-rearing, contributes hugely to global warming, a disservice to more than the animal species in question.
If you claim to be against cow-slaughter on grounds of avoiding cruelty, in the first place, you need to be against the slaughter of any species, at least, any species that expresses pain that you can perceive, and in the second, you need to turn totally vegan, since most animal products entail some cruelty in their extraction. Feel free with the urine and dung though – no cruelty there, and no bullshit.