Add a default per-cow tax, and deduct from it for purchase of a seaweed feed, and make it bite sufficiently that it becomes substantially cheaper to include seaweed in the feed.

This is how Norway encourages bottle recycling: There's no law mandating recycling of bottles, but there's a substantial tax on beverage containers that you get a reduction of in proportion to your return rate. This has resulted in a return rate of 99%+ of recyclable bottles by making it economically beneficial for retailers and distributors to participate in fairly elaborate and expensive collection and recycling schemes.

It takes some work to get mechanisms like this in place in a way that isn't easy to exploit, but get the incentives right and you can let economic interests do most of the work.

US does the same actually. $.05 tax on all bottles, $0.05 payment for recycling. It used to get people to recycle but now the penalty is too small to be worth it. On the flip side, rooting through garbage cans for recycling deposits is now a viable source of income for urban poor.

It's similar, but not quite the same. The above creates an incentive for people to collect bottles, but not an incentive for retailers to encourage bottle returns, which results in experiences for consumers that often makes it seem like it's not worth it. E.g. if you're forced to bring your bottles to a recycling centre instead of to the grocery store you're headed anyway, it's a lot less likely to happen.

Getting the incentives right across the whole chain is important.

E.g. I can't rememember ever seeing an automated bottle return machine like these [1] [2] in a US grocery store. It's been a few years, so it may have gotten more widespread, and I know some states have had return laws that have been more effective, so I'm sure it depends on location. In Norway the norm is for most grocery stores and shopping centres with any stores that sell bottles to have those.

Part of the reason is that in Norway, if people don't return bottles, the cost for retailers and distributors go up (or more precisely, their tax does not go down) by more than the cost of the recycling, so it's not just consumers that are incentivised, but retailers and distributors too, with the result that there's a massive infrastructure targeted at making it easy to return (and as a result one of the largest manufacturers wordwide of automated return solutions is Norwegian as well).

I currently live in the UK, which is much worse than the US when it comes to bottle rturns, and really wish the above solution would become more widespread.

[1] https://en.wikipedia.org/wiki/Reverse_vending_machine

[2] http://www.wikiwand.com/no/Flaskepant#/Panteautomater

Here in Germany stores have to take back single-use containers with deposit. Small stores are allowed to only accept the brands they sell, larger ones have to take everything.

In Brazil it worked out in a similar fashion: poor people would seek for aluminum cans inside garbage and then sell it for recycling companies. So it was a cheap source of aluminum, companies would get enough profit to continue in business, and some people made a living out of it.

After some while, giving more marketing about "going green" and calculating that money was being throw at the garbage, some stores like restaurants and supermarkets began to collect those aluminum cans. Profit for then, recycling still being profitable to companies, poor people lost this income they have fomented.

On the other other hand, we're essentially paying urban poor to empty cans and strew garbage over the sidewalk.

They never make a mess where I live. They know to never become a nuisance of the cops will start to harass them.

My experience from growing up in Norway and living in the UK, is that there's far more littering related to bottles in the UK, where people will throw them all over the place, than in Norway where they almost always get returned.

I guess that could work.