This study was conducted with the objective of quantifying the effect of zerorngrazing on the biogas and slurry production in Fogera woreda throughrngrouping cattle in to two main categories, i.e., zero grazers and free grazersrnhaving four cattle in each groups and collecting data accordingly. Both biogasrnand slurry production were measured by taking two biogas plants that fed withrnmanures of zero grazing and free grazing cattle separately. The parameters onrnwhich data were collected are manure production, manure fed to biogasrnplants/influent, slurry and biogas production. The interpretation andrndiscussion were carried out based on descriptive statistics through comparingrnand contrasting the data/ the parameters between zero grazing and freerngrazing. The result shows that zero grazing has significant effect on thernproduction of manure, slurry and biogas. There was significant (P0.05)rndifference between the amount of liquid manure fed to the two biogas plantsrnwhich resulted equivalent amount of biogas production per a unit of manurernfrom the two groups. Therefore, it can be concluded that, in addition to therndirect impact through over grazing and over stocking, free grazingrnmanagement system of cattle has significant indirect impact on thernenvironment by affecting the production of slurry and biogas which may be thernsilent impact of cattle management systems on the environment.rnKey words: Biogas, slurry/bio-slurry, feedstock/influent, zero/free grazing