The purpose was to estimate methane emissions and economic optimum in sheep under dry conditions with a maintenance diet, compare biopreparations of non-commercial microorganisms (PNC) and commercial probiotic REVET (R) (PCRE) at different concentrations in sheep in the semi -arid of Zacatecas. The experiment was carried out in El Remolino, Juchipila, Zacatecas, 21 Katahdin X Dorper cross sheep weighing 14.3 +/- 1.74 kg and maintenance diet were used. The PNC was included in T1 (100%), T2 (66%), T3 (33%), and a control T4, while the same conditions were applied to the PCRE in T5 (100%), T6 (66%), and T7 (33%). Weight was recorded and rumen content samples were obtained to quantify volatile fatty acids (VFAs), methane and ammonia. An analysis of variance was performed, and response functions were calculated to identify the economic optimum. Treatment T2 stands out, which used the PNC and showed the highest amount of VFAs with an intermediate production of methane, however, the best treatment was T6 PCRE of the microorganism biopreparation since it showed consistency in the production of VFAs and less methane concentration, but with a higher investment and lower economic gain. Microorganism biopreparations are an option for sheep producers with less investment capacity in the semi -arid region of Zacatecas.