Exploring Duckweed (Lemna gibba) as a Protein Supplement for Ruminants Using the Boer Goat (Capra hircus) as a Model

Abstract

Duckweed is the common name used to refer to members of the aquatic plant family Lemnaceae. Duckweed commonly grows on stagnant, nutrient enriched waters throughout tropical and temperate zones. Growth conditions include water temperatures of 6 — 33°C and a wide pH range. Under ideal conditions, duckweed can double its biomass every sixteen hours to four days. Its nutrient uptake capability helps to account for a CP of 15 — 40% and high growth rate. Scientists have studied duckweed's feed attributes for fish, poultry, swine, and ruminants. A duckweed feeding trial was carried out at North Carolina State University Metabolism Educational Unit with 19 goat wethers fed four different diets. The objective of the trial was to characterize the composition of wastewater grown duckweed and evaluate its use as a protein supplement for ruminants. Our hypothesis was that duckweed is a suitable protein source for goats and will behave in a similar fashion to soybean meal. The diets included a negative control, positive control (all of the supplemental protein from soybean meal), 1/3 duckweed, and 2/3 duckweed (1/3 and 2/3 of the supplemental protein came from duckweed, respectively). The goats were fed equal amounts of hay and supplement at 4% of body weight (as fed). Duckweed exhibited a similar compositional profile to soybean meal except for being lower in CP and higher in minerals. Amino acid and protein fraction profiles were also comparable between duckweed and soybean meal. There was no significant difference among treatments for DMI, ADF, and NDF digestibility. Nitrogen intake, N digested (g/d), and N retained (% of digested) showed no significant differences among the supplemental protein diets. Nitrogen retained as a percent of intake and N retained (g/d) tended to be slightly lower in the diets containing duckweed. Serum urea nitrogen levels also showed no significant differences for the protein diets except for a linear response (P = 0.09). The P balance showed no significant difference for P intake but both linear and quadratic responses for P retained (g/d), and P digested (g/d) as well as a linear response for P retained (% of digested). Similarities of the rumen pH, NH₄ and VFA data among the diets show that duckweed does not abnormally affect rumen function and is comparable to soybean meal in dietary function. Duckweed appears to be a viable source of protein and phosphorus (at lower dietary levels) supplementation for ruminants and is nearly comparable to soybean meal in its utilization.