The mother is not giving enough milk the calf is starving. It is eating off the ground and any grass ect. it stained the teeth. If it get enough milk until it gets the age it should be before it eats solid food the teeth will not stain.
Just sold two mother and babies today because of this. The older one just before death when he was brought in and started feeding, His teeth were brown stained after a week or so on the bottle and care the stain was gone.
Was chatting with the vet this morning and ask him. Too much floride, too much iron, LA-200 all while the cow is pregnant will cause it. There is also a geneic thing that causes it but he couldn;t recall the name. Those were what he came up with off the top of his head
She is a beef calf crossed. I dont know exactly you can see a picture of her on the post (same calf still subject of pneumonia) She has several other issues. If she lives she will be our little farm mascot for a long time.