Difference in load factors are due to the way they are measured:
MAD-BOH: 49%-according to data published by CAA, considers passengers actually flying the route.
MAD-BOH: 57%-according to Ryanair, considers just bookins made on the route (passengers paying for their flight).
Compared with other routes out of MAD, BOH is not doing very well (EMA had last month a 69% LF -data from CAA-). I would say the very early departure from MAD (around 6 am) is not helping much, but the same could be said of other routes (Eindhoven or EMA) that are working pretty well.
In any case, itīs a bit too early to make any judgement, as these routes are only 4 months old