Beef packer margins improved for the sixth straight week to put returns at their highest point in two years. The increase in margins came despite a pullback in beef values as packers were able to push fed cattle prices even lower and increase profits. The big concern for packers in the next 3-4 weeks is whether beef prices follow their seasonal move lower and how much power packers have to lower fed cattle bids if that pressure emerges.  Feedlot profit margins ...