Primarily this is an economic decision. On farms of less than 75 acres, horses have been well demonstrated to have lower overhead costs than tractors, and therefore increase profit per acre worked. Oxen have even lower overhead costs than horses, and since I only have 17 acres their slower pace is not an impediment to me.
We need the oxen primarily to harvest hay. Our land is about 1/3 hay field, with the potential of nearby rentals, and we have had trouble getting it harvested the way we like, when we like. There are raking and baling attachments available for the little BCS tractor, but that is going to cost me 12k in new hardware, plus all the gas I’ll spend every year, and it still leaves me without a great way to move the 6+ tons of hay out of the field. The oxen can put up loose hay with used antique wagons, mowers, rakes, and hay loaders for much less, and harvest all their own fuel in the process. At the end of their working life, they are worth almost as much as beef as what I put into them. The loose hay tends to be of a higher quality than baled hay, due to reduced leaf shatter.
The downside of oxen is that they can’t just be parked when not in use like a tractor. To perform their best they need to work regularly, and even when out of shape they need daily care. They also have minds of their own and will need a lot of training in order for us to make a good team.
We have started a pair of oxen, you can keep up on the calves’ progress here.