Since each market hog is losing roughly $30, it would be reasonable to expect market weights to decline a bit. Lighter weight hogs could reduce per-head loses while also reducing the amount of pork on the market and thus giving a boost to prices. But, so far, weekly average carcass weights have been running 1 to 3 pounds heavier than last year.   Since marketing lighter hogs means marketing younger hogs, the best opportunity to accelerate shipments without disrupting the market will come in late summer when slaughter levels are seasonally low.