One of the major limiting factors of livestock production in Ethiopia is the very low quantity and quality of livestock feeds supplied in the country. This calls for seeking forages that complement poor quality feeds in the country. Hence, the target of this article was to compare three types of grass agronomic performance, yield, and chemical composition under three different agroecologies and three harvesting dates (60, 90, and 120 days). The field experiment was carried out in selected three districts in 2017/2018 in the main cropping season. The treatments were laid out in a factorial RCBD (the randomized complete block design) arrangement with three replications. The treatments contained the combinations of three altitudes and three harvesting dates. Agronomic, yield, and chemical composition data were collected from the current study and subjected to analysis of variance procedures with a
P
<
0.05
significance test. In most agronomical and chemical compositions, the interactions of altitudes and harvesting dates were significant for all tested grasses (Mulato II, Napier, and Rhodes grasses). The highest plant height (PH) and dry matter yield (DMY) by Napier and the number of tillers per plant (NTPP) by Mulato II were recorded. There were significant values (
P
<
0.05
) for DMY and CP for all grasses at the interactions of harvesting dates and altitudes. The significant difference in DMY was observed as the harvesting date advanced, but CP was contrariwise. Of all tested species, the highest crude protein value and the least value of NDF and ADF (best forage quality parameters) were recorded by Mulato II. Thus, the results of this study revealed that Brachiaria hybrid cv. Mulato II has great potential to fulfil the demands for quality feeds for livestock production, especially at low altitudes. Nevertheless, in areas where, Napier and Rhodes grass are available, they can be alternative forage for Mulato II grass. Generally, for effective utilization of the tested grasses, the comparative feed value for animals must be conducted.