Beef packer margins plunged $105/head last week to $36/head as higher cattle prices combined with declining wholesale beef values to sharply compress packer profits. Fed cattle prices rose nearly $3/cwt to $227/cwt while the Choice cutout fell $4.75/cwt to $368/cwt. Margins have deteriorated $167/head over the past month but remain $169/head above year-ago levels, as packers have been able to control fed cattle prices while maintaining premium pricing on beef primals.  Feedlot placement margins deteriorated ...