The holocaust survivor most often making that analogy is called
Alex Hershaft. Another vociferous author is Charles Patterson, and Isaac Bashevis Singer is also an important Jewish author and holocaust survivor who became vegetarian for that reason. (I strongly endorse his book "
If this is a man", one of the strongest books on the Holocaust, mainly because it is written very dispassionately.)
To be honest, I personally do not like to use the Holocaust analogy, not only because it can be seen as insulting, but also as it is IMO factually wrong. The Nazis did not want to "use" Jews, they wanted to "exterminate" them, kill them and eradicate them from the face of the earth.
Slave owners, on the other hand, did not harbor any ill will towards their slaves. Many are reported to have treated their slaves "compassionately", they simply wanted to use them and did not think that they did matter morally. For that reason, IMO the slavery of people of colour has very many similarities to the slavery of nonhuman animals.
In Germany, there are many left-wing people who adamantly reject the documentary "Earthlings" because it references the holocaust and even call everybody who refers to "Earthlings" as a Nazi or right-wing person. (Unfortunately, there also ARE right-wing and anti-semitic animal rights activists in Germany who use rather unsavoury comparisons, which does not make the whole thing easier). As I said, I do not like to use the Holocaust analogy, but I can only find it ironic when Germans tell Jewish people (Hershaft, Patterson, Singer) using that analogy that they are insulting Jewish people...
And no, I am not equating either Coloured people or Jews with animals. I am actually comparing white, yellow, green, purple, brown and whatever other kind of human animals (in short: EVERYBODY) with nonhuman animals.
Everybody who is insulted by being compared to animals is IMO only speaking from a perspective of speciesm. You would have definitely "insulted" a Charlotte, NC, slave owner in 1830 by suggesting that coloured people are just as human as he is.