This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
馲 combines 馬 (horse) with 乇, but the exact historical development and original meaning are uncertain.
With 馬 (horse) on the left and 乇 on the right, this kanji might relate to a horse or pack animal, but its meaning is unclear.
For タク, imagine a horse carrying a heavy tack: tack -> タク, and the horse 馬 is loaded with gear.