A few different explanations.
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U.S. red-meat production during December, at 4.1 billion pounds, was up slightly from a year earlier, mainly because of a recovery in pork production, as beef slaughter and production declined according to the latest Livestock Slaughter report from USDA.

With cattle numbers and slaughter numbers down, the report shows heavier slaughter weights helping temper the decline in beef production. Overall, beef production during December, at 2 billion pounds, was down 2 percent from December 2013. Cattle slaughter meanwhile, at 2.4 million head, was down 5 percent. Average live weights were 29 pounds heavier than a year ago, at 1,363 pounds, helping compensate for the drop in slaughter numbers.