The biggest factor affecting the current upswing in popularity for forage brassicas in the U.S. may be their concurrent suitability as cover crops. Many producers are attracted to the prospect of improving their soil while also feeding their livestock.

An explosion in seed availability and new varieties hasn’t hurt either.

The brassica family of crops was developed by selective breeding and crossbreeding of a few species into many forms designed for different uses as forages, vegetables, oilseeds and cover crops.

In the U.S., the old stand-by brassica forages are turnips, rape and kale. Newer additions to the roster include swedes (rutabagas), forage collards, mustards, radishes and a seemingly unlimited list of interspecies hybrids. There is a brassica available to fit almost every cropping niche. However, if your primary reason for growing them is grazing, be sure to select varieties intended for that purpose.

Some rape and radish varieties are selected for high levels of secondary compounds to combat soil pests in crop rotations, and these varieties may lack palatability for grazing purposes.

Brassicas that form big bulbs, such as turnips, swedes and radishes, can be grazed but are less suitable for multiple grazings than varieties that do not elevate their crowns on top of bulbs.

However, there are turnip and radish varieties selected for grazing that have an increased proportion of top growth relative to the bulb.

Forage brassicas are best suited to use by grazing. Their extremely high moisture content makes preservation as a hay crop impractical. I have measured standing turnip forage at 4 percent dry matter.

No, that is not a typo; you do the math, 96 percent water. I have heard reports of brassica silage being attempted, but no reports that the results were satisfactory. It is a certainty that any chance of ensiling success would require mixing the wet brassica crop with another forage with greater dry matter content.

The beauty of brassicas as a grazing crop is their outstanding cold tolerance that allows them to provide high-quality pasture well into the fall and winter when almost all other forages are dry and brown. Little new growth will occur after temperatures fall below freezing at night, but existing forage remains and holds nutritional value very well.

Livestock readily learn to dig up brassica forage under modest amounts of snow, where the freezing temperatures preserve the forage.

Another strong point is a fast growth rate that, under good growing conditions, can provide emergency forage in as little as 45 days. Forage brassica yields are quite variable, ranging from 2 to 5 tons of dry matter per acre depending on species, variety and location.

Nutritionally, forage brassicas behave like a high-moisture concentrate feed. Crude protein is typically sufficient to meet needs of pastured livestock. Brassicas are naturally low in ruminally effective fiber compared to grass and legume pasture.

Brassica neutral detergent fiber (NDF) ranges from 11 to 44 percent and has NDF digestibility up to 70 percent. Brassicas that form stems (rape and kales) will be at the higher end of that range, and leafy brassicas like turnips and radish will be at the lower end. Ash content is approximately 10 percent. The balance of the dry forage content is non-fiber carbohydrates (NFC) that are quickly fermented in the rumen.

On a dry matter basis, turnip roots can contain more NFC than corn grain. This high nutritive value can produce excellent animal performance but requires adjustments to grazing management.

No one would expect livestock to perform well if abruptly switched from a perennial pasture to diets consisting solely of high-moisture corn grain, but this is essentially what we ask if we move them to pure brassica pastures with no transition time.

Animals should be introduced to brassica-based pastures slowly to allow the rumen time to adapt and should never be grazed on pure brassica pastures.

Effective fiber can be provided by planting brassicas in mixtures with small grains (oats, rye or wheat) or other forages, supplementing pastures with hay or providing access to a separate grass pasture. A good rule of thumb is to limit brassicas to no more than 75 percent of the diet.

Brassica forages do best on productive, fertile, well-drained soils and do not tolerate waterlogging. They are responsive to N fertilizer up to 100 pounds per acre, which should be applied in split applications before planting and about three weeks post-planting. Phosphorus and potassium should be applied according to a soil test.

Boron application may be beneficial if grown in sandy soils or soils low in organic matter. Brassicas can be established using conventional tillage, no-till or aerial seeding but are relatively weak seedlings. Optimal establishment requires chemical or physical suppression of competition from existing plants in the first three weeks of growth.

Seeding rates are 2 to 4 pounds per acre for turnips, 4 to 5 pounds per acre for swedes, 5 to 6 pounds per acre for rape and kale, and 4 to 20 pounds per acre for radish.

There are brassica varieties suitable for planting any time from 50ºF soil temperature in spring to six weeks before a killing frost, thus fitting many windows of opportunity for annual forages. Kale and swedes need a full growing season for best yields, rapes and hybrids need 60 to 90 days, and turnips and radish can be ready to graze in 60 days.

Radishes will bolt if planted in spring, reducing yields for grazing and potentially spreading seeds to be problematic in subsequent crop rotations. Most forage brassicas will winterkill when temperatures fall below 10ºF, but in the South some cultivars may overwinter and bolt in the next year if not grazed out.

Brassicas are often grazed as a once-over annual crop, but many rape, turnip and grazing radish types will regrow and provide multiple grazings if managed for that purpose.

Brassicas that form bulbs are best used for once-over grazing because crowns are easily damaged by hooves; if regrowth is desired, be careful to leave at least 4 inches of stubble to protect the crowns.

Rape regrowth occurs from side buds on stems and leaving about 10 inches of stubble provides plenty of stem buds for regrowth. Strip grazing improves forage utilization by reducing trampling losses.

Forage brassicas are an excellent choice for pastures in need of renovation. It makes little sense to take out a productive perennial pasture for an annual forage. Chemical kill of the failing pasture followed by fall grazing of brassicas will produce an ideal seedbed for planting a new perennial pasture the following spring.

This system also helps prevent buildup of brassica root diseases by ensuring brassicas are not planted more than two years in a row in the same location.

No forage is without potential health problems for animals, and brassicas are no exception. In fact, brassicas boast a frightening list of potential issues for grazing livestock, including nitrate toxicity, bloat, photosensitization, goiter, poliomalacia, rumen acidosis, anemia and pneumonia. Fortunately, none of these problems seem to be common under production situations in the U.S.

In general, potential problems can be minimized by feeding brassicas as no more than 75 percent of the dietary dry matter intake, introducing animals to brassica pasture slowly, never turning hungry animals onto a brassica pasture, providing a trace mineral supplement that includes iodine, not grazing immature rape (safe maturity is indicated by a reddish/bronze tint to leaves) and avoiding excessive N and S fertility. I am interested to learn of any animal health problems experienced on brassica forages.

Plenty of anecdotal evidence suggests feeding brassica crops too close to milking time may impart off flavors to milk. Research indicates a three-hour withdrawal prior to milking is long enough to prevent this problem.

Research also indicates grazing brassica pastures can improve flavor scores for lamb, although some anecdotes indicate the opposite effect. I am currently involved in research at Michigan State University to determine the effect of grazing brassicas on flavor of grass-finished beef. Watch out for future reports on management and utilization of this very versatile forage.  FG

PHOTO: A turnip-rape hybrid with oats, shows growth rate six weeks after planting. Photo courtesy of Kim Cassida.