By Jessica A. Williamson
Cool season perennial pastures typically experience a reduction in production from the end of June on through the summer, and although they pick up production in the fall, the overall biomass produced is significantly less than that of the spring. Forage brassica crops include kale, turnip, radish, rape, and swede. These forages can be seeded in the spring to extend grazing into the summer when permanent cool season pastures are experiencing the summer slump, or in the late summer to extend grazing into the fall after permanent pasture productivity has slowed.
These forages are annuals and will not survive a killing frost; therefore, they will cease growing after the first killing frost of the fall. Brassicas do well mixed with other cool or warm season annual forages, depending on the growing season in which they are intended to be grazed. This helps to diversify the forage available, along with allowing the opportunity for greater biomass. Forage quality of brassicas can be very high, with crude protein levels ranging from 15 to 25% in the herbage portion of the plant. However, although these forages have very high quality, they can have up to 80% moisture. The best way to graze brassicas is to offer livestock other forages that will fill the rumen and reduce the incidence of brassica-related disorders.
Improper grazing management of brassicas can result in serious health disorders to the grazing animal, including bloat, nitrate poisoning, atypical pneumonia, hemolytic anemia, hypothyroidism, and polioencephalomalacia. The incidence of these diseases can be greatly reduced by offering livestock other forages such as long stem hay or grazing them in a mix of brassicas and grasses. Also, livestock should not be turned into a field of brassicas for the first time on empty stomachs; ensure that they have grazed on permanent pasture or have eaten long stem hay prior to being turned onto brassicas. The diet should be comprised of less than 75% brassicas, even after the rumen has been fully adapted.
In order to utilize as much of the forage as possible, strip grazing should be used to manage when, where, and how much the brassicas should be grazed. Implementing a forward and back fence will allow control of the grazing and improve the ability to achieve targeted residual height, improving the possibility for regrowth and subsequent grazing.