Throwing dead cows into a sieged city could work. Citizens trapped inside walls and being forced to deal with the disease, inability to bring in more food, and rampant disease. It might not make them surrender, but it could passively kill enough they could no longer defend.

But in the modern day this stands no chance of working. The conditions don't exist for that possibility l. Instead it depletes your reserves, emboldens your enemy, and makes them fight harder.

And in this case it doesn't even reduce your enemies war capacity. Ukraine is being fed their war material. They don't need anywhere near as much local production. On the other hand, no one is feeding Russia any significant amount of war material and cannot produce it as fast as they are using/losing it.

Russia is still fighting as if it's the 1600's. And when you look at their history? It's really no surprise. They've been fucked since the black death.