Ok, I admit that right after the holiday of Purim, religious Jews (well at least those in charge of house cleaning) start to get a bit weird. Furniture might get covered, rooms are taped shut, children (and sometimes, the husbands) seem to have disappeared from the planet when help is needed, and the usually sane home will often take on a "tinge" of tension.
Different groups among Jews have different degrees of accepting what food one can and cannot eat. My wife once mentioned that is we accepted everyone's bit of weirdness concerning what one can and cannot eat on Pesach, the result would be a week-long fast!If you look at the food products that are available, you will find indicators that a certain food is "Kosher for Pesach", some also include the information "with/out kitniyot" (which is another weird discussion on its own!). But these indicators also have various degrees of acceptance, and some of them, say an American-made chocolate bar, will have a very good indicator ("heksher") and be without kitniyot, and is considered by most (excluding the minority who refuse to consume milk that does not have a "cholav Yisroal" label) fine for eating.
One week before Pesach, and only in Israel, as far as I can tell, most of the cows are no longer fed their normal feed, which is "chometz", but is switched to a "kitniyot" feed. The major Israeli milk buyers, such as T'nuvah, require this, and if you want to sell your milk to them, you abide by their rules. As a joke, I mentioned to a woman that since she nurses her child, and since she only has one stomach while a cow has two, that a kal-v'komer should be that she stops eating chometz one week before Pesach as well.
Let's just say that this suggestion was met without any degree of acceptance, and I was rightfully ignored! Of course, she is not planning to sell it to an Israeli chocolate company, so my argument doesn't hold water.
So everywhere else in the world, the cows keep eating their oats (or whatever they feed them), except in Israel, and yet products from both will have a "Kosher for Pesach" label. Now it certainly cannot be that they consider that the milk produced from a cow, after it's multi-pass system, has the attributes of what it takes in, because, if that were so, then only those who can eat kitniyot would be able to use the milk that comes out during Pesach from Israel, and there is no such labeling on the Israel milk containers.
So why is it done? Certainly not because the output takes on the input attributes, or else the milk would be labeled as kitniyot. And not because the feed might fall into the milking pail (most milking doesn't have some lone person on a small stool squiting milk into a pail these days), because that would be a concern outside of Israel. Remember, I am talking about the period that is before Pesach, in which there is no dispute if one may benifit from chometz.
The fact is, it is just another one of those weird things that some people do, and we go along with it in our own brand of weirdness.
