CHICAGO, Jan 21 (Reuters) - CME Group live cattle futures gained on Thursday ahead of a closely watched monthly Cattle on Feed report, due out on Friday from the U.S. Agriculture Department.Traders anticipate the report will show fewer cattle heading into feedlots, as recent rallies in the grain market have increased feed costs."The incentive, for the last three months, has been to limit the cattle you place," said Altin Kalo, economist at Steiner Consulting Group. "It becomes more and more expensive to add pounds inside the feedlot."