A hay trolley (aka hay carrier, hay unloader) rolls on a track at the very top of the barn and made the filling of large barns with hay and bedding a manageable task.

From ProgressiveForge.com:Company records indicate William Louden received a U.S. patent for the world’s first hay carrier on September 24, 1867. In 1868 the first cast iron hay carrier appeared. The development of malleable iron, as opposed to cast, eventually led to all metal hay carrier designs that were stronger and longer lasting. A brake was designed in the carrier which would hold the load; taking the weight off the draft rope and the horses. Hay carriers of the 1880s limited the farmer to only one draw along the barn. He would have to climb to the top of the barn and reverse the carrier and/or the draft rope. Introduction of the Swivel Car and Swivel Reversible models resolved this problem. A design common by 1885 used a ring separating the trolley mechanism from the car. Eventually various styles of steel track, were introduced making the carrier system much easier to operate.Carriers needed to be simple, dependable and strong enough to support the loads. Downtime with a valuable crop on the ground could quickly result in a disastrous loss.