Beef packer margins fell for the sixth straight week and were negative for the third week in a row. Margins are estimated at -$217/head – down $100 on the week - pressured by a sharp rally in fed cattle prices and weaker beef values. WPI forecasts that packers will see deeply negative margins through the holiday season as cattle prices are predicted to rise and outpace pre-holiday beef market strength.  Feedlot profitability was mixed last week as ...