The objective of this work was studying the diet of extensively reared bovines that decreases the emission of greenhouse gases. The study took place in a farm called Campo Dorado located in the district of Huallanca, in the province of Bolognesi, department from Ancash, in Peru. In this study, the sample selected was 4 Brown Swiss cattle between 4 to 5 years of age and weighing between 470 to 570 kg, they were chosen for a population of 70 cattle from the livestock, which were conditioned in chambers separated, specially prepared for monitoring, as the sample. The closed chamber technique was performed on 4 groups (differentiated according to the type of diet followed in the study) with 2 monitoring teams and lasted 5 days. The control group's diet was green grass from the research area, while group 1 had a diet of oat silage, group 2 of oat hay, and group 3 of a mixture of silage and hay. The reductions achieved for methane emissions were: in group 1 the reduction was 16%, for group 2 the reduction turned out to be 29% and for group 3 it was 9%. Regarding the reductions achieved with carbon dioxide for groups 1 and 2, they were 33% and 61% respectively, while for group 3 there was an increase of this last gas by 4%. Therefore, it was concluded that oat hay is the most appropriate diet for reducing greenhouse gas emissions in extensively reared cattle.