Jehovah’s Witnesses: Should we ume blood was part of Abel’s offering to God?

that's an interesting question "Marvin", I'll bite because I'm bored. While, there is no explicit statement, Abel most likely did not drain the blood, as Jah had not commanded them to drain the blood out of the animals yet because they did not [or, were at least not supposed] to eat them (until after the flood, when Noah was first given meat to eat). Abel's sacrifice had blood while Cain's did not (vegetables which obviously did not have blood). While God is not recorded as stipulating what the sacrifice was to be it would be pertinent to remember that in the Mosaic law lesser sins were atoned for with grain and barley and the like but serious sins were atoned for with sheep, goats, bulls, etc. (fat and blood inlcuded). As the second generation of humans they were both under a heavy weight of sin (of their parents) so therefore, while the Bible is not explicit, blood was probably important. (but that's just my opinion)