Effects of Feeding Brachiaria-Based Diets Supplemented With Desmodium and Dairy Cubes On Cattle Manure Greenhouse Gas Emissions

Abstract

The study evaluated the effect of protein concentrate (dairy cubes) and leguminous forage containing condensed tannins (Desmodium intortum) on diet digestibility and their impacts on manure greenhouse gas emissions. Leguminous forages containing condensed tannins (CT) have the potential to reduce manure nitrous oxide (N2O) and methane (CH4) emissions and improve diet digestibility and utilization. The objectives of the study were to determine the effects of two protein supplements on (1) the nutritional value and digestibility of diets, (2) manure characteristics, and (3) manure greenhouse gas (GHG) emissions. Twelve lactating crossbred cows were fed three dietary treatments: diet 1 (D1) control (Brachiaria only), diet 2 (D2) Brachiaria + dairy cubes, and diet 3 (D3) Brachiaria + Desmodium in a completely randomized design with four cows per diet. Total feces and urine from individual cows per diet (n=4) were collected. The manure was incubated in glass jars at 20 °C for 84 days, and CH4, N2O, and CO2 emissions were measured. Objective one involved proximate analysis, i.e. dry matter (DM), crude protein (CP), fibre analysis, and in-vitro degradability of dietary treatments. Objectives two and three involved analysis of manure samples taken at days 0, 7, 14, 28, 56, and 84 of incubation for water content, total carbon (TC), total nitrogen (TN), fibre, and CT and gas samples for GHG emissions. From the findings, apparent N digestibility differed significantly between dairy cube and desmodium supplemented diets (67.9 ± 2.59 % vs 55.3 ± 2.63%). Excreted N was higher in excreta from cows receiving N supplementation (dairy cubes and Desmodium) than control diet, both for fecal N (61.2 ± 2.62 and 62.5 ± 2.55 vs 42.7 ± 1.90g N day-1), and urine N (66.9 ± 4.38 and 34.1 ± 0.93 vs 35.9 ± 0.87g N day-1). Condensed tannins were higher in feces excreted by cows fed Desmodium supplemented diet than dairy cube supplemented diet (0.82± 0.07 vs 0.09±0.06% DM). Manure cumulative GHG emissions were similar across the diets. However, due to variations between experimental animals, diet effects on manure GHG emissions were not conclusive. From this study, diet composition influenced manure composition. Desmodium is recommended as an alternative protein supplement to expensive concentrates, but harvesting time should be considered for higher nutritional value and animal productivity.