Duckweed and its utilization as a feed supplement
Duckweed is a native, free-floating plant that can be seen on the surface, and is a bright, vibrant green. It is recognizable by its flat oval shape, varying slightly based on the variety, and is about 1/16 to 1/8 inches long with a singular root that dangles down below the surface. Duckweed species are small floating aquatic plants found worldwide and often seen growing in thick, blanket-like They are monocotyledons of the botanical family Lemnaceae and are higher plants or macrophytes, although they are often mistaken for algae. Duckweed reproduces by budding and fragmentation and floats in large colonies.
Duckweed (Lemnaceae spp.) farming is gaining attention as a combination of water purifier and fish and animal food in developing countries. Duckweed is a hardy plant, fast-growing, protein-rich and requires only simple technology. Organic wastes can be used as a nutrient source, and necessary trace minerals can be provided for its well growth. Crop management concerns include temperature extremes, nutrient loadings, nutrient balance and pH. These can be controlled via proper fertilization, irrigation, harvesting methods and buffering.
HABITAT AND CLIMATIC CONDITION
Duckweeds grow at water temperatures between 6 to 33°C. Duckweed survives at pH’s between 5 and 9 but grows best over the range of 6.5-7.5. For optimum growth water temperature above 60°F is beneficial. Duckweed species are adapted to a wide variety of geographic and climatic zones. They are found in all but waterless deserts and permanently frozen areas. They grow best in tropical and temperate zones and many species can survive temperature extremes. Many species of duckweed cope with low temperatures by forming a turion and the plant sinks to the bottom of a lagoon where it remains dormant until warmer water brings about a resumption of normal growth. The natural habitat of duckweed is the surface of fresh or brackish water which is sheltered from wind and wave action. They do not survive in fast moving water (>0.3 m/second) or water unsheltered from wind which is an important attribute as they do not become weeds in water ways. A duckweed leaf is flat and ovoid. Many species have adventitious roots which function as a stability organ and which tend to lengthen as mineral nutrients in water are exhausted.
Compared with most plants, duckweed leaves have little fibre (5% in dry matter of cultivated plants) as they do not need to support upright structures. Roots, however, appear to be more fibrous. As a result, the plant has little or no indigestible material even for mono-gastric animals. This contrasts with many crops such as soya beans, rice, or maize, where approximately 50% of the biomass is in the form of high fibre, low digestibility residues. Duckweed rich in protein (25-50%). Duckweed protein has a better array of essential amino acids than most vegetable proteins and more closely resembles animal protein.
|Nutritive Value||Contents on dry matter (%) for duckweed|
USING DUCKWEED AS A FEED/SUPPLEMENT
The composition of duckweed depends on the nutrient content of the water and the prevailing climatic conditions. Harvested duckweed plants contain up to 43% protein on a dry weight and may be used without further processing as a complete feed for fish. It is, therefore, a source of high quality protein to be exploited for domestic animal production. Duckweed grown on nutrient-rich water has a high concentration of trace minerals, K and P and pigments, particularly carotene and xanthophyll, that make duckweed meal an especially valuable supplement for poultry and other animals, and it provides a rich source of vitamins A and B for humans too.
Use of duckweed in fish nutrition
- Duckweeds grown on water with 10-30 mg NH3-N/liter have a high protein content around 40% of high biological value. Fresh duckweed is highly suited to intensive fish farming systems with relatively rapid water exchange for waste removal and duckweed is converted efficiently to live weight by certain fish including carp and tilapia.
- A duckweed lagoon with a standing crop of duckweed is harvested and placed fresh into a second lagoon containing a mixed size tilapia culture. The pond is harvested twice weekly and the fish sorted into various groups for return to the lagoon or sale. Under these circumstances the average yield of fish per hectare of lagoon is estimated at around 10 tons annually using only duckweed as the supplement to the naturally available fish feed.
- Fish production can be stimulated by feeding duckweed to the extent that yields can be increased from a few hundred kilograms per hectare/year to 10 tonnes/ha/year.
- Duckweed is a convenient feed for fish. Its attributes are:
- It can be readily grown locally often in waste ponds that are polluted.
- It can be fed fresh and since it floats, by judicious setting of the rates of application it may be totally used by fish.
- It is used very efficiently by fish such as tilapia and carp but other species might well cope with duckweed as a component of the diet since it is particularly low in fibre and high in protein when grown under ideal conditions.
- It is relatively inexpensive to produce or may be regarded to have no cost where the opportunity costs of family labour are not taken into consideration.
Use of duckweed in poultry nutrition
- The potential nutritional value of duckweed in poultry diets has long been well recognized in poultry nutrition.
- Dehydrated duckweed has been used to replace alfalfa (lucerne) meal as a protein source in conventional poultry diets.
- Chickens fed 10% dehydrated duckweed had superior weight gains to those fed conventional protein sources.
- Recent studies have demonstrated that the growth of very young broiler chickens may be retarded with increasing levels of duckweed dehydrated meal in the diet whereas layer hens produced effectively and older broiler birds had excellent growth when fed relatively high levels of duckweed meal.
- Duckweed can replace conventional protein and energy sources in chicken diets up to 25% of the total dry matter.
- This indicates that duckweed of known chemical analysis can be used in least-cost ration formulation for both poultry meat and egg production.
Use of duckweed in pig nutrition
- Research with a low protein/high fibre duckweed meal (23% N x 6.25 and 7.5% fibre in DM) showed that replacing conventional protein sources in diets for growing pigs reduced production and increased feed required per unit growth.
- Studies using wet and dry duckweed and conventional (grain-based) or non-conventional feeds (eg: sugar cane juice or molasses) are urgently needed. If systems based on non-conventional feeds were to be successful they would support small farm enterprises of great significance.
- Pigs can use duckweed as a protein/energy source with slightly less efficiency than soyabean meal.
Use of duckweed in Ruminant nutrition
- Very little literature is available on the utilization of duckweeds by ruminants.
- Duckweeds grown on nutrient-rich waters have the potential to be of high nutritional value particularly for the young or lactating ruminant and preliminary observations suggest that they might form the basis of a supplement to diets based on mature biomass such as crop residues, mature grass or pasture.
- Even the high water content, softening the straw, let alone the nutrients they provide would facilitate the use of straw by ruminants.
- Ruminants fed mature biomass such as straw are generally deficient in a range of minerals and ammonia for efficient fermentative digestion of the straw in the rumen and in addition for maximum efficiency of feed utilization they require supplements containing proteins that escape the rumen environment to be digested in the intestines. With ruminants, therefore, it is necessary to describe the nutritional role that is required of the duckweed before assessing its feeding value.
- A duckweed:maize silage diet (2:1) produced higher growth rates in Holstein heifers (about 200 kg LW) than a maize silage:concentrate:grass diet, without any detrimental effects.
Proteinaceous feed resources are generally in short supply, and in addition are usually the most costly components of the diets of most animals in developing countries. Duckweed presents a protein source that is of great potential for feeding to domestic animals and particularly fish. The nutrients in the water upon which the duckweed is grown critically affect its nutritional value particularly for monogastric animals where the fibre and protein contents of the duckweed are important elements. For ruminants, high levels of duckweed are not so crucial but feed processing to ensure the protein bypasses the rumen is probably necessary. The potential for duckweed resides in its use as a sole fish feed or a component of fish diets where it can be used at the site of production for fish cultivation. Duckweed appears to be potentially a major resource for the poultry industries of developing countries and could be incorporated into poultry diets on a least cost basis.
Duckweed meal may have great potential to blend with non- conventional diets based on inexpensive carbohydrate sources that can be used by pigs and ducks. With the possibilities for growing it with high protein and fat content, it would then blend extremely well with sugar cane juice or molasses and with other low-protein root or tuber producing carbohydrate crops such as cassava and sweet potatoes. These unconventional diets lend themselves to small scale integrated farming operations that include pigs.