Introduction to Leucaena leucocephala
Known by many names, including the 'white lead tree' or 'ipil-ipil,' Leucaena leucocephala is a fast-growing, tropical legume tree native to Central America. For decades, it has been cultivated worldwide for its numerous benefits, including its use as animal fodder, firewood, and its role in improving soil fertility through nitrogen fixation. However, the plant is famously known for its dual nature: possessing a high nutritional value comparable to alfalfa, but also containing the toxic, non-protein amino acid, mimosine. This comprehensive analysis will explore the rich nutritional composition, while also addressing the risks associated with its antinutritional factors.
High Macronutrient and Protein Content
One of the most notable features of Leucaena leucocephala is its high protein content, which is a primary reason for its use as livestock fodder. The leaves are particularly protein-rich, with crude protein levels typically ranging from 20% to 30% of dry matter, depending on the plant's maturity and growing conditions. Young, tender leaves often have a higher protein concentration than more mature foliage. In contrast, the seeds contain an even higher average crude protein content, reported to be around 31.9% of dry matter.
Amino Acid Profile
The protein in Leucaena is also of high nutritional quality due to a favorable amino acid profile, often compared to that of soybean meal or fishmeal. It is a good source of several essential amino acids. Key amino acids found in Leucaena protein include:
- Arginine: A significant amino acid present in both leaves and seeds.
- Leucine and Isoleucine: Branched-chain amino acids important for protein synthesis.
- Lysine: An essential amino acid often a limiting factor in many plant-based proteins.
- Phenylalanine: Another essential amino acid found in substantial amounts.
Essential Minerals
Beyond protein, Leucaena is a notable source of essential minerals, which vary depending on soil composition. Analysis of leaf meal reveals several key mineral concentrations:
- Calcium: Excellent source, with tender leaves having significantly higher concentrations.
- Potassium: High concentrations are often found in the leaves, contributing to overall plant health.
- Phosphorus: Present in moderate amounts, though the concentration can be lower than required for some livestock.
- Magnesium: Good levels are found in the leaves.
- Trace elements: Important trace minerals such as iron, zinc, and manganese are also present. However, sodium is typically low and may require supplementation for ruminants.
Key Vitamins and Carotenoids
Leucaena leaves are also rich in certain vitamins and carotenoids, which are vital for animal health. Most notably, the plant contains a high content of beta-carotene, a precursor to vitamin A. The leaves are also a source of vitamin K. The presence of xanthophylls, a type of carotenoid, has been shown to improve the pigmentation of egg yolks and broiler carcasses in poultry.
The Challenge of Mimosine
The primary constraint on the use of Leucaena in animal feed is the presence of mimosine, a toxic, non-protein amino acid. Mimosine concentration is highest in the youngest tissues, such as new shoots and seeds, and decreases as the plant matures. This compound is particularly detrimental to non-ruminant animals like pigs, poultry, and horses, where it can cause hair loss, reduced feed intake, and other toxic effects.
Antinutritional Factors Explained
In ruminants, such as cattle and goats, mimosine is broken down in the rumen into another toxic compound, DHP (3,4- and 2,3-dihydroxypyridine). DHP is a goitrogen, which can cause enlarged thyroid glands and affect reproductive performance if ingested in high amounts over long periods. Fortunately, specific rumen bacteria (Synergistes jonesii) can detoxify DHP. These bacteria can be transferred to non-adapted animals to alleviate toxicity. In addition to mimosine, condensed tannins are also present in Leucaena, which can reduce dry matter digestibility but also offer a benefit by protecting some protein from rapid degradation in the rumen.
Nutritional Comparison: Leucaena Leaves vs. Alfalfa
| Nutrient | Leucaena leucocephala Leaves (% DM) | Alfalfa (% DM) |
|---|---|---|
| Crude Protein (CP) | Avg. 23.3 (Range 14.2–33.3) | Avg. 15.7 (For comparison) |
| Crude Fibre (CF) | Avg. 19.9 | Avg. 31.5 |
| Ash | Avg. 8.5 | Avg. 16.6 |
| Beta-carotene (mg/kg DM) | ~500 | ~250 |
This table highlights that Leucaena leaves, on average, contain a higher crude protein content than alfalfa, with lower crude fiber, potentially indicating a higher nutrient concentration per unit of mass. However, the presence of antinutritional factors like mimosine, not found in alfalfa, necessitates careful management.
Nutritional Variations by Plant Part and Maturity
The nutritional composition of Leucaena varies significantly with the plant part and its stage of maturity. Tender leaves and young shoots contain higher levels of crude protein and mimosine than older, mature leaves. This means careful harvesting and processing techniques are needed to maximize nutrient benefits while minimizing toxicity. The seeds, while high in protein and energy, also contain the highest concentrations of mimosine and other antinutritional factors.
Conclusion
Leucaena leucocephala is a highly nutritious and versatile tropical legume, offering a wealth of nutrients, including high-quality protein, a balanced amino acid profile, essential minerals like calcium and potassium, and important carotenoids and vitamins. Its use as a valuable fodder source for livestock, particularly ruminants, has been widely recognized. However, the presence of the toxic amino acid, mimosine, and other antinutritional factors like condensed tannins, requires careful consideration and management. Effective processing methods and biological strategies, such as inoculating ruminants with detoxifying bacteria, can mitigate the risks associated with mimosine toxicity, allowing for safe and beneficial integration of Leucaena into animal diets. For comprehensive nutritional data, a reliable source like Feedipedia is invaluable (https://www.feedipedia.org/node/282).
