By SCOTT McFETRIDGE DES MOINES, Iowa (AP) — Like other ranchers across the country, Rusty Kemp for years grumbled about rock-bottom prices paid for the cattle he raised in central Nebraska, even as the cost of beef at grocery stores kept climbing. He and his neighbors blamed it on consolidation in the beef industry stretching back to the 1970s that resulted in four companies slaughtering over 80% of