Aside from all the berries, same as real world I guess. Organics eat organics.
Honestly, you're looking too deep into it. There are loads of elements to the Pokemon world that make little to no sense. But being reasonable, they must be eating Pokemon.
Pokemon are stronger and more intelligent than regular animals I believe, so having a Tauros farm just to make meat, I don't think so, I don't think any Tauros would let that happen. They still have a mind of their own and strength that could easily kill humans, so raising Pokemon for food is highly unlikely to me.
Think of the bigger picture. You've also got Pokemon called Charizard, for example. Who is almost certainly a voracious meat eater and will be hungry often. Trainer explains the situation to Charizard, Charizard will be quite happy to assist in corralling and killing all those Tauros for meat.
It's never really dealt with in the games 'cos it doesn't really need to be. There are some minor references to food stuffs but that's mainly to berries. But it's a video game and those don't usually deal with real world necessities such as eating, sleeping and defecating.
Then there's the anime, which is aimed at kids. I mean, it's so aimed at kids that they won't even write in the bratty little **** getting told off 'cos they're worried the audience won't understand and will get the wrong message. So of course they don't go near the subject. That means talking about... y'know... death.
Does make me laugh though... of everyone commenting, a majority likely meat eaters... Getting squeamish over the idea of the eating of meat... Damn, I can be a smug vegetarian sometimes.