Brassicas require thoughtful grazing management
Interest in grazing brassicas is on the rise. In effort to extend the grazing season, producers are planting more turnips and radishes. And, as sod-seeding techniques are further fine-tuned, I expect to see even more livestock grazing brassicas.
Brassicas such as turnips or radishes produce high yields of nutrient-rich leaves and roots. They make good grazing. These crops have been helpful at two critical time periods in the year, midsummer and late fall to early winter. Summer-planted turnips may be the best grazing option for late fall and winter. But, like everything else, they can cause problems. Problems that might arise from feeding turnips include hemolytic anemia, polioencephalomalacia, pulmonary emphysema, nitrate toxicity, infertility, bloat and goiter. That’s a nice list of scary stuff, but you can avoid most problems with proper management.
Basic strategies for managing brassica grazing are similar to how you handle alfalfa or lush spring pasture.
Don’t start feeding turnips suddenly and extensively. Instead, let cattle adapt to a richer diet by feeding high quality forage for a couple weeks before grazing turnips.
When you do introduce the herd to brassicas, allow access for just a few hours a day. While grazing turnips, continue to provide a dry forage source like grass hay or corn stalks.
You can restrict grazing area to limit access as well as encourage full plant consumption.
Use an electric wire or tape to stripgraze. This will encourage animals to eat the leaves and bulbs.
Provide a mineral supplement. Providing a supplement with monensin (Rumensin) improves the energy value of the diet. Feeding monensin is helpful in reducing the incidence of pulmonary emphysema (ABPE). ABPE is most likely to occur when mature cows quickly move from a coarse forage base to a lush, high-quality forage base. It’s technically caused by the metabolism of tryptophan, an essential amino acid. In the rumen, lactobacillus bacteria convert tryptophan to 3-methylindole, a toxic compound that causes lung damage, edema and emphysema.
You may hear about choking risks from brassicas like turnips, but the only case I have ever verified was on drought-stricken turnips that had bulbs the size of carrots, and the animals had limited feed availability. Cows do chew.
Turnips can be very productive, they grow fast and can be grazed as early as 70 days after planting. They reach near maximum dry matter yields at 80 to 90 days. The protein content will be high in the leaves-often in the mid 20s on a dry matter basis. Leaves are 10 to 18 percent of the total plant mass. Bulbs make 82 to 90 percent of the mass.
If you plan to grow turnips or other brassicas, your fertility program is best determined by soil test and MFA agronomist recommendations. My experience is that phosphorous and potash recommendations are similar to a small grain crop, and 70 to 80 pounds per acre of nitrogen is needed.
For a source of turnip seed, MFA offers the purple top white bulb forage turnip, product #2612540 and the Barkant turnip, product #2612585.