Russian Comfrey: A Double-Edged Sword in Nature
Russian comfrey ($Symphytum imes uplandicum$) is a perennial herb cultivated worldwide for its lush growth and impressive nutrient accumulation, primarily for use as a green manure or animal fodder. The plant's deep root system allows it to draw significant quantities of minerals and nutrients from the soil, making it a powerful resource in organic farming and livestock management. The "Bocking 14" strain, a sterile hybrid of Russian comfrey, is particularly favored for its high yields.
The Nutritional Profile of Russian Comfrey Leaves
Analysis of the dry matter of Russian comfrey leaves reveals a robust nutritional composition. The leaves are notably high in protein and various minerals, which is why they have historically been incorporated into the diets of cattle, pigs, and poultry.
Protein Content:
- Russian comfrey is considered moderately rich in protein, with average dry matter values around 18.6%, though figures as high as 29.3% have been documented.
- This protein includes various amino acids, such as tryptophan and methionine, offering a rich protein source for animals.
Mineral Composition:
- Potassium: Extremely high levels, with an average of 70.1 g/kg DM, making it a valuable source for this essential mineral.
- Calcium: A solid source of calcium, averaging 18.7 g/kg DM.
- Iron: Contains significant iron, averaging 4125 mg/kg DM.
- Phosphorus: Provides phosphorus, with an average of 4.9 g/kg DM.
- Magnesium and Copper: Also contains magnesium and copper in notable amounts.
Critical Safety Information: The Dangers of Pyrrolizidine Alkaloids
Despite its high nutrient density, Russian comfrey contains toxic compounds known as pyrrolizidine alkaloids (PAs). PAs are liver-toxic chemicals that can cause serious and irreversible damage, including sinusoidal obstruction syndrome (veno-occlusive disease) and, in some cases, liver failure and cancer.
- The most toxic PA, echimidine, is found predominantly in Russian and prickly comfrey, in higher concentrations than in common comfrey.
- The PA content varies depending on the plant part (roots have higher concentrations) and maturity.
- The U.S. Food and Drug Administration (FDA) has advised manufacturers to remove all comfrey products intended for oral consumption from the market due to these risks.
The Use of Russian Comfrey in Animal Feed
While unsafe for human consumption, Russian comfrey has been historically used as a forage crop for various livestock. Studies have noted its benefits and potential drawbacks depending on the animal.
- Pigs and Poultry: The fresh leaves are palatable to pigs and poultry, and their low fiber content makes them an efficient feed additive.
- Ruminants (Cattle and Sheep): Some animals may find the hairy leaves unpalatable, but wilting or ensiling the crop improves acceptance. The nutritive value for ruminants is well-documented.
- Palatability and Nutrient Digestibility: The plant's palatability varies by species, but digestible nutrient content can be comparable to other fodder crops like berseem.
Comparison Table: Russian Comfrey for Animal vs. Human Use
| Attribute | Animal Feed (Livestock) | Human Consumption | Comment |
|---|---|---|---|
| Protein | High (15-30% dry matter) | Not applicable | Excellent protein source for livestock. |
| Minerals | Rich in K, Ca, Fe, Mg | Not applicable | Provides essential minerals for animal health. |
| Pyrrolizidine Alkaloids (PAs) | Present, but often managed in feed | Present, highly toxic | PAs are a major hepatotoxic risk for humans. |
| Consumption Safety | Managed and proven in feeding trials | Unsafe (potentially lethal) | Oral intake is banned by the FDA. |
| Recommended Use | Animal fodder, green manure | Topical only (on unbroken skin) | Topical use requires caution and medical consultation. |
Topical Use and Cautions
While oral consumption is strictly prohibited, comfrey is sometimes used topically in creams and salves for external applications, such as for bruises and sprains. However, even this use is not without risk, as the PAs can be absorbed through the skin, and it should never be applied to broken skin or used for extended periods. Always consult a healthcare provider before using topical comfrey preparations. For more authoritative information on the toxicity, visit the NCBI Bookshelf LiverTox database.
Conclusion
What is the nutritional value of Russian comfrey is a question with a two-part answer. For livestock and agricultural purposes, it offers significant nutritional benefits due to its high protein and mineral content. However, for human consumption, the nutritional value is irrelevant because the plant is a known health hazard. The presence of toxic pyrrolizidine alkaloids makes Russian comfrey unsafe for oral ingestion and necessitates extreme caution even with topical applications. The serious and potentially fatal risk of liver damage means it should be viewed strictly as an agricultural resource and never as a food or internal supplement for humans.
