Harvesting for silage
The crop can be harvested from R3 to R6. Soybeans harvested at R3 to R5 will produce high quality forage and have lower oil content than those harvested at R6. The higher oil content may cause fermentation problems. However, soybeans harvested at R6 will produce more dry matter. Mow the crop with a mower conditioner equipped with roller crimpers. Experience from Wisconsin indicated that flail conditioners cause more damage and dry matter loss than roller conditioners. As with alfalfa, soybeans should be allowed to wilt in the field to 65% moisture before chopping.
Feeding soybean hay
Soybean hay has a tendency to cause bloat in cattle, so it should be fed carefully. Mix the soybean hay with grass hay or fill the cattle up on grass hay prior to feeding soybean hay. Horses can safely consume soybean hay if it is baled and stored properly.
Feeding soybean silage
Feed quality of soybean silage is equivalent to alfalfa haylage. Soybean silage is less palatable than haylage or corn silage. However, it can make up 15 to 20% of a dairy ration without impeding animal intake or milk production. The exception is when the soybeans are harvested after the R6 stage is reached as more seed (higher oil content) is present, which can affect fermentation and palatability.
Staton writes for Michigan State University Extension