Effects of supplementing tropical dairy cows with different dietary protein sources on nitrogen excretion and manure greenhouse gas emissions

Abstract

In Kenya, commercial concentrates and leguminous forages are widely used as protein sources in dairy production. However, little is known on their impact on manure greenhouse gas emissions. This study compared manure chemical composition, nitrogen excretion rates, and methane and nitrous oxide emissions in a controlled laboratory experiment. Fresh manure was collected from lactating dairy cows fed on a basal diet of Brachiaria (Brachiaria brizantha cv. Xaraes) hay (control, CON) and supplemented with either Desmodium (Desmodium intortum) hay (DES) or dairy cubes (CUBES) and incubated in 1 L mason jars at 20 °C for 84 days. Results showed that DES and CUBES supplementation increased nitrogen excreted both in faeces (1.81±0.02% DM, 1.68±0.10% DM) and urine (0.76±0.05%, 0.75±0.07%) compared to the CON (faeces: 1.35±0.02% DM, urine: 0.35±0.02%). These findings suggest that protein supplements affect manure composition, though in-situ studies are needed to understand their impact on manure emissions.