Brassicas for Forage

Information from Ohio State University, Cornell University & Penn State University research

Forage brassicas are high quality, high yielding, fast growing crops that are particularly suitable for grazing by livestock. Both tops (stems plus leaves) and roots (bulbs) can be grazed and are very nutritious. Brassicas can be seeded (1) from mid April through May for summer grazing or (2) in July or August for fall/winter grazing. All members of the brassica  (or cabbage) family - turnips, rape, kale, and swedes - produce forage of exceptionally high (often 85-95%) digestibility. Brassicas are valuable to produce high quality forage either (1) during the critical summer period of slowed pasture growth and/or (2) to extend grazing into the late fall-early winter period.

Turnips and rutabagas are short-season root brassicas that provide roots, stem and leaf growth for rotational grazing or strip grazing 70 to 90 days after seeding. The leaves can be grazed from mid- September until January depending upon critical low temperatures and snow cover. Top growth generally will survive temperatures between 15-20 degrees F, while bulbs will be about 5 degrees hardier. The common purple top garden type as well as Rondo, Pasja and other forage varieties, yield up to 7000 lb/acre of dry matter. The tops have 17-30% crude protein while roots contain 12-15% protein. Trials in New York in 2007 of Pasja turnip and oats produced forage with a average crude protein of 30.5 and a NEL of 0.74. Some new forage-type turnip varieties such as All Top produce relatively more top dry matter than roots. Turnips are seeded from mid July to mid August at rate of 2-3 lb/acre and produce maximum yields approximately 90 days after seeding.  As long as the top of the root is not removed in the first grazing, turnips can be ready for regrazing in about 30 days.

Rape is a short-season leafy brassica whose stems and leaves are ready to harvest (rotationally graze, strip graze or green chop) 90- 120 days after establishment. Plants develop a reddish tinge when ready for harvest. Rangi, Windall, Dwarf Essex, Winfred and Emerald varieties have performed satisfactorily in Penn State University trials. Leaving a ten-inch stubble will facilitate rapid regrowth. Rape leaves and stems have lower protein level (14-17%) than turnips. Rapes can attain yields of 8000 lb/acre dry matter if planted during May or June. Rape can be planted as late as August 1, but with lower potential yield when planted late. Seed at 3-4 lb/acre rate.

Kale generally has shown highest yields of all brassicas with up to 12,000 lb/acre dry matter production at 150 days. It has the greatest cold tolerance in the Brassica family, surviving temperatures down to 10 degrees F. This allows grazing of the leaves and stems by rotational or strip grazing into December and January most years.

While brassicas have been successfully used for centuries in Europe and other parts of the world for livestock feed, the following precautions should be noted. Brassicas are very high in crude protein and energy, but extremely low in fiber. Their low fiber content results in rumen action similar to when concentrates are fed; thus the need for proper roughage supplementation. Brassicas therefore should never comprise more than two-thirds of the forage portion of livestock diets with the remainder provided by grass hay or stockpiled pasture. All brassicas contain low levels of glucosinolate compounds which can be toxic, but adequate grass forage supplementation seems to prevent them from causing animal health problems.

Following these 2 rules can help avoid health problems -

- Introduce grazing animals to brassica pastures slowly. Avoid abrupt changes from dried-up summer

pastures to lush brassica pastures. Don't turn hungry animals into a new brassica pasture.

-  Brassicas should not constitute more than 75 percent of the animal's diet. Supplement with dry hay if  continually grazing brassicas or allow grazing animals access to grass pastures while grazing brassicas.

No-till establishment into existing sod will reduce the risk of these disorders because of grass in the brassica pasture. Nitrate poisoning has been documented from excessive nitrogen fertilization plus reported instances of high accumulation of calcium and potassium that can reduce the availability of magnesium to animals. Use feed analyses to check and modify mineral balance of animal diets. Excessive fertilization of both nitrogen and potassium should be avoided. Most dairymen have avoided off-flavors in milk by preventing brassica consumption two hours before milking. Others prefer to only feed rapes to lactating dairy animals when they also feed plenty of grass roughages.

Strip grazing where forage is rationed every day or two provides the most efficient usage. Rape, kale and mustard have regrowth potential if not grazed below six inches. Turnips will regrow if the growing point at the top of the bulb is not removed. Two or more cycles should be possible with rotational grazing if rainfall is adequate but brassicas can be green chopped and made into baleage for confined animals and winter feeding.