Methane and nitrous oxide emissions from excreta of different beef cattle breeds fed with different concentrate:roughage ratios and finished in feedlots under tropical conditions

Abstract

Excreta from confined beef cattle are sources of greenhouse gas (GHG) emissions; however, little is known about the effects of different concentrate:roughage ratios and cattle breeds on these emissions. This study evaluates methane (CH₄) and nitrous oxide (N₂O) emissions from the excreta of Nellore or crossbred (Nellore × Angus) beef cattle that are fed diets containing 65% or 85% of concentrates under tropical conditions. The excreta were applied to the floor of feedlot pens, and N₂O and CH₄ emission rates were monitored for 84 days in static chambers. The animals were confined for 106 days to evaluate their intake, weight gain and feed efficiency. In addition to average emission rates, emissions from excreta were estimated based on ratios per kg of dry matter intake (DMI; CH₄/DMI and N₂O/DMI) and per kg of weight gain (average daily weight gain, ADG; CH₄/ADG and N₂O/ADG). The data were subjected to variance analysis in a 2 × 2 factorial arrangement, and the means were compared using a Tukey test (P < 0.05). Results indicated that CH₄ emissions were 2.40 times higher from the excreta of crossbred cattle than in Nellore cattle (P < 0.039). N₂O emissions were 50.1% lower from the excreta of animals consuming diets with low concentrate:roughage ratios than in those consuming diets with high concentrate:roughage ratios. The CH₄/DMI and CH₄/ADG ratios were higher in the excreta of crossbred cattle than in Nellore cattle. The N₂O/ADG and N₂O/DMI ratios in the excreta of animals fed with high concentrate:roughage ratios were also 18.2% and 36.1% higher in crossbred cattle than in Nellore cattle. The N₂O/DMI and N₂O/ADG ratios in the excreta of crossbred and Nellore cattle were lower when fed with diets containing low compared to high concentrate:roughage ratios. The results suggest that crossbred animals with more concentrate feed diets emit more CH₄ and N₂O from their excreta. This is the first study to report that Nellore cattle, the predominant breed in Brazil, and diets with lower concentrate:roughage ratios may be associated with a reduced potential for GHG emissions from excreta in confined beef cattle under tropical conditions.