* Blizzard conditions curb beef production at some plants * Firmer wholesale beef prices lend futures support * Feeders sag with deferred live cattle contracts * Hog futures gain as wintry weather lifts cash prices By Theopolis Waters CHICAGO, Feb 25 (Reuters) - Chicago Mercantile Exchange live cattle futures rose for a third straight day on Monday following the U.S. Department of Agriculture's monthly cattle-on-feed report last Friday, traders and analysts said. The data showed higher-than-expected marketings in January against the first increase in the number of cattle placed on feedlots in eight months that stirred bullish spreads. Blizzard conditions in parts of the U.S. Plains are making it difficult to transport livestock to packing plants and move fresh product to customers. Cargill Inc's Friona, Texas, beef processing plant was not operating on Monday because road conditions made it impossible for trucks to move cattle and beef to and from the facility, company spokesman Michael Martin said. "Our Dodge City, Kansas, beef plant is operating only one shift today, with both shifts scheduled for tomorrow," he said. The Tyson Foods Inc beef complex in Amarillo, Texas, was also idled by Monday's storm, said company spokesman Gary Mickelson. Packers on Monday processed 87,000 head of cattle, down 22,000 from a week earlier and 33,000 less than a year ago during the same period, based on USDA data. "As a result of the storms last week and today's storm, feedlot conditions have deteriorated significantly ... and cattle weights are likely to fall sharply," Hales Trading Co president David Hales said. Reduced slaughters since late last week slowed the movement of fresh beef to grocers and other buyers while lifting wholesale beef prices and improving packer margins. The wholesale price for choice beef on Monday was $183.09 per cwt, up 20 cents from Friday; select cuts slipped 5 cents to $180.14, according to the USDA. HedgersEdge.com put the average beef packer margin for Monday at a negative $42.25 per head, compared with a negative $50 on Friday. Investors were waiting for feedlots to count the number of cattle available for sale. Cash-basis cattle last week fetched $123 to $125 per cwt, which was steady to $2 higher than the previous week, feedlot sources said. Spot February live cattle closed at 126.950 cents per lb, 0.600 cent higher. Most-actively traded April ended up 0.200 cent to 128.425 cents. CME feeder cattle were weakened by deferred live cattle contracts and firm corn prices. March feeders settled 0.450 cent per lb lower at 140.800 cents. April ended at 143.700 cents, down 0.075 cent. HOGS REBOUND ON WEATHER Hog futures posted modest gains in anticipation that cash hog prices would trend higher in the near term, which spawned short-covering, analysts and traders said. "Packer margins have improved significantly after they lowered cash hog bids for almost a week. Weather is supposed to get worse before it gets better, so packers are going to be hurting for supplies," a trader said. USDA data showed the average price for hogs in the most-watched Iowa/Minnesota market on Monday at $76.26 per cwt, 83 cents higher than Friday. The average pork packer margin for Friday was at a positive $5.45 per head, compared with a positive $2.95 on Friday, according to HedgersEdge.com. April hogs ended at 81.900 cents per lb, 0.250 cent higher. June closed up 0.100 cent to 91.050 cents.