Each year, as the holiday of matzot approaches and people prepare to clear their homes of all things leavened, Israel’s dairy farmers embark on a similar journey, for their cows.They clean the milking machinery and feeding troughs, hose down the food mixers and clean out the stables.In order to serve up milk that is kosher for Passover, not a grain of hametz (leavening) can remain in place.“The prohibition of hametz on Passover applies to the property of Jews, and not just his food,” said Eviatar Dotan, head of the Israel Cattle Breeders Association.“Even animals are considered property, and therefore it is forbidden, according to Halacha, for cows to eat hametz.”Israel’s 130,000 dairy cows are fed a kosher-for-Passoverdiet free of grains, based mostly on beans, corns and chickpeas. That’s right, Israeli cows eat hummus for passover.“A Jew’s animal is forbidden to consume products that become hametz,” said Peretz Shorek, who coordinates the food centers for the Beef and Dairy Growers Association.“When an animal eats, it secretes saliva. When the saliva drips onto one of the five grains, it turns them into hametz, therefore it is forbidden to feed the animal the five species of grain,” he said. The animals have sensitivity to dietary change, so the process begins early and occurs gradually. The cows don’t suffer any health problems, according to Shorek.The costs of making cows kosher for Passover vary from year to year, depending on the prevailing difference in the market price of grains and the kosher-for-passoverdiet that year. Consumers don’t see a change in prices because it is calculated ahead of time and incorporated into the price of dairy throughout the year.Technically, any imported dairy product that wants to be approved as kosher for Passover must go through the same process, though few do.As a result, homegrown Israeli dairy products have a market advantage with the kosher for passover crowd.According to Shorek, the practice has gone on for decades in Israel.“This is halacha. Before this, it was just not followed to the letter of the law,” he said.But if dairy cows need to eat kosher for passover food to produce kosher for passover milk, why doesn’t the same hold true for animals used for meat? According to Ziv Maor, a spokesman for the Chief Rabbinate, the dairy producers have got their halachic reasoning backwards. “It’s not that hametz is processed through the body into the milk,” he said. “The main reason for changing the food is that it might touch the body.” If a piece of stray hametz were to find its way onto a cow’s udder or otherwise make its way into the dairy, it would contaminate the whole batch.The same worry does not apply to beef cows, which have their skin removed before they are cooked and eaten. Chickens, on the other hand, which are cooked and eaten with their skin, also must be in a hametz-free environment, Maor said.