The price of lean hog futures for October delivery has jumped by more than 3% on CME Group in the past week, as pig farmers in the US and Canada warn that a rise in feed prices will force them to cut the size of their herds in the coming months.

The rise in livestock prices comes after the long summer drought in the American Midwest pushed up the prices of crops and grains farmers use for feed. That in turn has pushed up the benchmark price index for the US pig-farming industry: the CME's Lean Hog Index.