Nutritional composition and heavy metal contamination in antelope grass (Echinochloa pyramidalis) in Kampala metropolitan area

Abstract

Urban livestock farming in Kampala, Uganda, is increasingly relying on wetlands for forage, particularly Echinochloa pyramidalis (Antelope grass) for their livestock due to a short supply of feed. These wetlands however experience the discharge of industrial effluents and municipal wastewater which exposes the grass to heavy metals, which raises concerns about heavy metal contamination and associated risks to livestock and public health. The aim of this study was to evaluate nutritional quality, heavy metal levels, and potential health risks from Antelope grass harvested from polluted and non-polluted wetlands in Kampala metropolitan area. Samples of Antelope grass were analyzed for proximate components (crude protein, crude fiber, total ash, ether extracts), detergent fibers ADF & NDF, macro minerals (calcium, total phosphorus), and heavy metals including lead, cadmium, chromium, copper, iron, zinc, cobalt and nickel using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) and mercury using Atomic Absorption Spectroscopy (AAS). Metals from the Daily Intake of Metal (DIM) were estimated for dairy cattle and the local Mubende goats. Data were compared to safety thresholds from the East African feed standards, EU, FAO/WHO and NRC. Nutritionally, Antelope from polluted wetlands had higher crude protein (18.03 to 18.58%) in comparison to the Kabanyolo site (13.17% CP) but lower fiber fractions. Heavy Metal analysis indicated that Antelope grass from the Lubigi and Namanve sites were above the permissible limits of Lead, Cadmium and Chromium for both in forage and in a complete feed. Antelope grass 1 kilometer away from the sewage treatment plant downstream was considered safer than the ones upstream. Health Risk assessment via estimated DIM for Lead, Cadmium, Chromium and Copper from polluted wetlands being above the lowest toxic daily thresholds to cattle with significant risk to goats as well. While Antelope grass from polluted wetlands has high nutritional value, it is associated with heavy metal contamination, which presents serious health risks.