Today, agriculturists are facing the challenge of an increasing feed supply for livestock, poultry, and pisciculture. To keep pace with the escalating demand of the major feedstuffs, growers are struggling for an increased supply of animal feed. The shortage of animal feed supply has emerged as the principal problem with the expansion of the poultry and livestock industry. Finding sustainable and economical raw materials to be processed to final feed products is a major source of concern for the feed industry (Fagbenro et al., 2003; Adikwu, 2003; Adejinmi, 2000). The rising cost of conventional animal feed has driven agriculturists to switch to every second option of non-traditional feedstuffs. The alternative of the cheaper non-conventional feed can affect the cost of the ultimate product. Animal nutritionists, therefore, have engaged themselves in finding alternative nonconventional nutritional resources for their animals (Ngou and Mafeni, 1983).
Man has benefited from the aquatic ecosystem since time immemorial. Hydrophytes constitute the biotic component of the aquatic ecosystem which is the baseline of aquatic biodiversity. This implies that water plants are nutritionally rich and play a pivotal role to sustain the life of aquatic animals. Most of the water bodies are inhabited by aquatic weeds that grow vigorously under favorable climatic conditions (Whetstone, 2005). If not managed properly most of the aquatic plants may have a considerable detrimental effect on the habitat directly or indirectly (Lancar and Krake, 2002).
Aquatic weeds are defined as the undesirable vegetation growing in water which if kept unchecked may substantially harm other aquatic biology. With progress in aquatic research, it has become evident that most of the aquatic plants have organic composition making them eligible to be used as animal feed. Aquatic macrophytes thus can play the role of non-conventional feed and can be utilized on a sustainable basis. Among aquatic weeds, the duckweed (Lemna minor) is a potential candidate to be used as an economical source of animal feed in a developing country like Pakistan. The plant belongs to the family of tiniest flowering plants the Lemnaceae. It is one of the smallest flowering plants, rich in protein and mineral contents, and can absorb nitrogen, phosphorus, and metals efficiently from water (Logsdon, 1989. It is a free-floating macrophyte about 3.5-10 mm in size, which thrives in the aquatic habitats of the globe. The genus Lemna is distributed among 12 species worldwide with 5 species occurring in Pakistan (McClure & Alston 1966).
Globally, soyabean meal is used as the frequent source of feed because of the higher protein percentage (Vang et al., 2001). Lemna minor is as rich in protein content as soyabean meal (Porath et al., 1979). It is one of the cheap sources of minerals and pigments like beta carotene and xanthophylls (Journey et al., 1993) and contains tenfold higher of them as compared to land plants (Mbagwu and Adeniji, 1988). Many other research works show the use of duckweed as potential feed for poultry (Samnang, 1999; Islam et al., 1997; Leng, 1995; Haustein et al., 1990). Duckweed fed to 3-weeks older chicks up to 5% of mixed feed caused higher weight gain (Truax et al., 1972).
Duckweeds can proliferate rapidly on the surface of stagnant water giving a smooth green look to the water body and acclimatize a broad spectrum of environmental conditions. The plant, having a short life cycle can produce several generations in a short period if favorable environmental conditions are achieved (Journey et al., 1993). The plant can thrive and replicate most excellent in water with 06-33ºC and can tolerate low temperatures and frost. The dry biomass yield of duckweed ranges between 10-30 tons per hectare annually with a good profile of dietary protein and essential amino acids (Leng et al., 1995).
Imbalance in mineral nutrition highly retards the growth rate and multiplication of the plant. Variation in growth media results in the changeability of the proximate composition of the biomass. In comparison to other growth media, duckweeds grown in hog wastewater manifested a relatively higher content of starch (Cheng and Stomp 2009). The contents of protein in the plant are related to the minerals in the growth medium of the plant.
As the growth of the plant is highly dependent upon the availability and balance of nutrients. The present investigation is aimed to determine whether a change in concentration of Nitrogen and Phosphorus, like other environmental factors, influences the biochemical composition of the plant.