Here is some more information about rusthållare.
A rusthållare provided horsemen for the cavalry regiments established within the Allotment System (Indelningsverket).
A farmer in a cavalry rusthåll had a personal contract with the Crown stating that he had to provide a cavalryman, horse and uniform. The contract was a voluntary agreement between the crown and the proprietor of an independent farm.
The farmer in a cavalry rusthåll was called a rusthållare
Just like in the infantry, the cavalrymen also were provided with a croft (ryttartorp) and a piece and to farm.
In order to provide a cavalryman with a horse and uniform the rusthåll farmer got a large tax reduction. In some cases the rusthåll farmer had an extra farmer (augument) assigned to help covering the expenses for the cavalryman.
The rusthåll farmer was also was exempted from military service.
The infantry soldiers within the Allotment System were recruited and provided in slightly different manner than the cavalry horsemen. The infantry used a system with rote farmers. The system with rote farmers was compulsory for the farmers. Some farmers were exempted from being a part of a rote though. That had to do with the classification of land and the land ownership.
Here is more information about the Allotment System:
http://www.algonet.se/~hogman/slsoldat_eng.htm Hans Högman