Enables alpha-1,6-mannosylglycoprotein 6-beta-N-acetylglucosaminyltransferase activity. Acts upstream of or within protein N-linked glycosylation. Located in Golgi apparatus. Is expressed in nervous system and neural ectoderm. Orthologous to human MGAT5B (alpha-1,6-mannosylglycoprotein 6-beta-N-acetylglucosaminyltransferase B). [provided by Alliance of Genome Resources, Apr 2022]