One of my Mini Nubian does had a still born baby buck yesterday. It was TINY. About the size of a Nigerian kid. She normally kids large healthy kids. Today there was what I thought was a placenta in the goat shed, but it turned out to be a very premature baby. The poor thing didn't even have fur.
What could've caused this?
I am sorry for your loss. There are many things that could cause a goat to abort. To start, the kid could have had a congenital anomaly, leading to a spontaneous abortion. Certain diseases could cause abortion, three big ones are toxoplasmosis, campylobacter, and chlamydia (most common), but there are others too, like . Other causes are nutritional deficiencies, trauma ( like a hard headbutt to the abdomen from another goat) or ate something poisonous.
Always be careful when handling an aborted kid and the placenta. I guess since there are so many illnesses (some that are zoonotic to humans) that cause abortion, you need to treat the kid like it is infected, even if it might not be (hah, can you tell I work in the medical industry? Yay standard precautions!). It might be good to contact your vet regarding the abortion, they may want to test the fetus. Or if it is too late to test, be sure to properly take dispose of it, like burying it deeply or burning.
Since I don't know as much about nubians or mini nubians, but I'd assume there is a risk they could inherit the genetic disease G6S (G-6-Sulfase deficiency). I know it causes failure to thrive in kids who inherit two copies of the faulty allele, but I am not sure if it can cause an abortion, too.