Trial Site: Fairview Research Farm
Research Coordinator: Dr. Akim Omokanye
From: Peace Country Beef & Forage Association 2017 Annual Report
Brassicas are a group of closely related plants, which include cabbage, cauliflower, kale, rape, radish, turnip, rutabaga and swede. Grazing of forage brassicas requires careful management. Brassica crops can cause health disorders in grazing animals if not managed properly. The main disorders are bloat, atypical pneumonia, nitrate poisoning, hemolytic anemia (mainly with kale), hypothyroidism, and polioencephalomalacia. Although there are many management factors to consider, forage brassicas do provide producers with a high yielding, quality forage option at a time when most cool season grasses are not available. Annual forage brassicas can provide livestock producers with fast-growing, high yielding, quality fall pasture.
Methods
Project Site: Fairview Research Farm (NW5-82-3W6) on RR #35, MD of Fairview.
Previous crop: Oats for greenfeed in 2016 and 2015.
Site soil information (0-6” depth): Soil tests done at Exova laboratory (Edmonton) prior to seeding showed pH = 5.6 and soil organic matter = 8.0 %.
The field was cultivated (disked and harrowed) before seeding.
Experimental Design: Randomized complete block design in 3 replications in small plots (118.8 ft2 )
Brassica crops tested (treatments): 11 forage-type brassicas were seeded at recommended seeding rates as listed below:
1. Kale @ 4lbs
2. Bayou kale cross @ 4 lbs
3. Winfred forage brassica @ 4lbs
4. Dwarf Essex rape @ 4lbs
5. Fodder radish @ 4lbs
6. Tillage radish @ 6 lbs
7. Daikon radish @ 13 lbs
8. Hunter forage turnips @ 4lbs
9. Graza forage turnips @ 4lbs
10. Purple top turnips @ 3 lbs
11. Barkant turnips @ 4lbs
Seeding Date: Seeding was done on June 1
Seeding method: 6-row Fabro plot drill with 9” row spacing
Fertility (actual lbs/acre): 44 N + 100 P + 123K + 7 S
Spraying: In-crop spraying with Lontreal 360
Forage yield was determined on August 03 for tillage radish, fodder radish and daikon radish. For the remainder of the crops, harvest was done on August 21.
Results and Interpretation
Forage Dry Matter (DM) Yield (Figure 1)
Winfred forage brassica had the highest forage DM yield (8470 lbs/acre), followed by tillage radish (8098 lbs/acre), daikon radish (7979 lbs/acre) and then fodder radish (7517 lbs/acre) (Figure 1). The 3 radishes produced higher forage yields than the rape, kale and turnips.
Forage Crude Protein (CP) (Table 1)
The forage CP was highest for Hunter forage turnip (30.8% CP). The 4 turnip varieties had higher forage CP than other forage-type brassicas tested, while the radishes had lower forage CP than other brassicas. Generally, the forage CP from all brassicas was above the 11% CP requirements by mature beef cattle.
Energy (Table 1)
The forage total digestible nutrients (TDN) were generally above 60% TDN. With the exception of fodder radish and tillage radish, all brassicas met and far exceeded the TDN requirements of young and mature beef cattle.
Minerals (Table 1)
The forage macro and trace minerals were generally high for the brassicas.
All brassicas exceeded the Ca, K, Mg, Na, S, Fe (except daikon radish) and Zn requirements of young and mature beef cattle.
Only 4 forage-type brassicas (hunter forage turnip, dwarf Essex rape, graza forage turnip and daikon radish) had enough forage P for mature beef cattle.
Half of the brassicas tested did not meet the Mn requirements of mature beef cattle.
Feeding Concerns of Brassicas
Brassica crops can cause health disorders in grazing animals if not managed properly. Livestock health problems from grazing brassicas are relatively rare, but elsewhere brassica crops have been associated with some animal health problems. Here are some excerpts from a publication (from https://www.dpi.nsw.gov.au/ __data/assets/pdf_file/0003/146730/forage-brassicas-quality-crops-for-livestock-production.pdf) on monocrop brassicas or where large amounts of brassicas are included in cocktails:
The grazing of brassica crops for protracted periods can sometimes result in rumen stasis (rumen stops moving) and constipation. Affected stock will appear depressed and lack appetite.
Goitre (enlarged thyroid) - This is sometimes a problem in young lambs, where pregnant ewes have been grazing leafy brassica crops. Contact your veterinarian for advice on iodine supplements for lambs or supplements for the pregnant ewes.
Blindness - Occasional outbreaks of the condition that involves blindness, aimless wandering and unpredictable hyperexcitability are observed in cattle grazing brassica crops.
Kale Anaemia - This disorder (sometimes referred to as red water) can occur with all brassica crops, but is more common with kale crops. Anaemia is caused by excess levels of the amino acid compound S-methyl Cysteine Sulphoxide (SMCO) in the plant. SMCO causes a decrease in haemoglobin concentration and a depression of appetite. This condition tends to be worse when soil phosphorous is low and soil nitrogen and sulphur levels are high. Stock should be removed from the crop if they develop this disease.
Respiratory Problems - Grazing brassicas has sometimes been associated with cases of pulmonary oedema (fluid in lungs). Affected animals display respiratory distress.
Pulpy Kidney - Pulpy kidney is most common in young stock. Stock are most at risk when they have been on low quality feed for a period of time, and are then placed onto a highly digestible brassica crop. Vaccination is the best way to guard against this disease.
Researchers have discovered that these disorders can be avoided by adhering to two management rules: Introduce grazing animals to brassica pastures slowly. Avoid abrupt changes from dry summer pastures to lush brassica pastures. Don't turn hungry animals that are not adapted to brassicas into a brassica pasture. Secondly brassica crops should not constitute more than 20-30% of beef cattle's diet.