DUCKWEED AS A NON-CONVENTIONAL FORAGE FOR RUMINANTS IN THE TROPICS

Abstract

The high cost of grain-based concentrates and crop residues are increasingly affecting profitable ruminant farming in Nigeria because of inadequate green forage all year round. Duckweeds are aquatic plants which constitute a nuisance in an earthen fish pond. However, information about their forage value is limited. Hence, this study was conducted to evaluate the nutritive value, secondary metabolites and in vitro fermentation characteristics of duckweed from earthen fish ponds. Duckweed represented as T1, T2, T3, T4 and T5 from different locations were collected, dried and analysed for chemical composition and in vitro gas production using buffered rumen fluid from goats. Cumulative gas production was measured at 3 to 48 hours of incubation periods. Results indicated that crude protein content was similar, while NDF, ADF and ADL were significantly different, with mean values of 54.11 %, 29.53 % and 11.57 %, respectively. Saponin content (0.407 − 0.468 %) was higher than alkaloids (0.312 − 0.433 %) and total phenols (0.158 − 0.175 %). Calcium and phosphorus varied from 0.09 to 0.54 % and 0.01 to 1.05 %, respectively. Lead and cadmium ranged from 0.01 to 0.17 mg.kg-1 and 0.01 to 0.03 mg.kg-1, respectively. Gas from the insoluble fraction (b), potential gas (a+b), the rate (c) and volume (Y) of gas produced were comparable. Cumulative gas produced increased as hours of incubation progressed, with gas volumes higher (3.93 mL/200 g DM) at 48 hr and least (1.07 mL/200 g DM) at 12 hr post-incubations. Metabolizable energy was similar and ranged from 3.13 to 3.68 MJ/Kg DM. Organic matter digestibility was higher (40.58 %) for T1 and comparable with T5 (36.76 %). Short-chain fatty acids (ranged = 0.02 − 0.05 µmol/200 mg DM) were comparable. In vitro dry matter degradability (ranged = 24.00 to 39.67 %) was significantly different. In conclusion, duckweed from earthen fish ponds is fairly degradable in vitro, and the nutrient contents elucidate its forage value for ruminants.