I can tell you for sure that round up does kill animals. The last time i sprayed it in my garden a pigeon came down and ate some of the grass weeds id sprayed and it died within minutes. Ive never used it again.
There was also a problem in peoples allotments around here when they used animal bedding that had been sprayed with round up as a manure, the potatoe crops were either stunted or they died. I later found out that the farmers spray the wheat to kill the plant off so that they can harvest it quicker, so whatever use the seed and the straw is put to, has round up residues on it.