CHICAGO, Aug 21 (Reuters) - Chicago Mercantile Exchange live cattle futures firmed for a second session on Monday, supported by a bigger-than-expected drop in cattle placements in July, reported after market close on Friday.

"In terms of slaughter ready cattle, we're still relatively tight," said Austin Schroeder, analyst at Brugler Marketing.

In the U.S. Department of Agriculture's (USDA) monthly Cattle on Feed report, the agency reported cattle placements into feedlots during July totaling 1.62 million head, down 8.3% from 2022, versus analysts' expectations of a 5.5% decline.

Most-active October live cattle added 1.050 cents to 179.875 cents per pound. September feeder cattle firmed 1.800 cents to close at 250.325 cents per pound.

Extreme heat forecast for the U.S. Plains in the coming week could add stress to feedlot cattle, said Schroeder.

"Especially in the cattle that are in the last 30 days on feed, those are the ones you're the most worried about because they have the most risk of heat stress," he said.

Boxed beef prices eased, with choice cuts trimming 55 cents to $315.56 per hundredweight (cwt), while select cuts fell $1.03 per cwt.

Beef packers slaughtered 122,000 head on Monday, up from 119,000 last Monday but down 1,000 from the same day last year, the USDA said.

The lean hog market eased as cash hog prices continue a seasonal slide, analysts said.

The most-active October futures eased 1.500 cents to 80.625 cents per pound.

The CME's Lean Hog Index fell to 99.61 cents per pound, its lowest since July 11.

The USDA quoted the wholesale pork carcass cutout at $105.21 per cwt, down 96 cents from Friday. (Reporting by Christopher Walljasper; Editing by Shailesh Kuber)