There are also intricate rules on how an animal must be slaughtered to produce kosher meat.

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Since an immigration raid in May, the nation's largest kosher meat-packing plant has been scrambling to fill hundreds of jobs.

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For Hebrew National to be certified as glatt, Rabbi Fogelman says, it would have to use only glatt kosher meat.

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"It is much better than it used to be, " says Rabbi Fishbane, but "it is not certified glatt, " he says, referring to an even higher standard of kosher meat certification.

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Meat from animals slaughtered by means other than stunning - for example kosher or halal meat - will not have to be labelled as such.

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Religious Jews buy only kosher-certified products and they separate their meat and dairy foods.

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The FSA estimates that less than 1% of all meat produced in the UK is kosher.

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Usually, people will not eat as much meat overall when they practice this kosher separation, he said.

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