Only the very wealthiest of land-cultivating peasants owned large animals at the time, though (and pretty much never horses). Also, you wouldn’t feed human edible vegetables to animals, that would be very wasteful.
More importantly, these income taxes were based on rather small fraction of revenues, since they were only based on agricultural production, and not on household production. Obviously, it was extremely impractical to tax household production, and it still is. Importantly though, back then, typical household consumed much more of its own production as a fraction of all consumption than today, and as a result, less of their real income was taxed.
Here is a way to think about it: if you buy a shirt from someone, you might need to pay the sales tax. However, if you make your own shirt, you aren’t going to pay tax on it. Today, you wouldn’t actually do it, because other people can make a shirt with much less effort than you ever could, so it’s still worth it for you to buy someone else’s product and pay the tax, because the productivity gains of trade will more than pay for what government skims from the transaction. However, back before industrial revolution, the differences in productivity weren’t nearly as big, so it didn’t alway make much sense to specialize in everything and trade.