Animals reared in natural, outdoor conditions without nasty modern drugs yield healthier meat, right? Not necessarily.

Wondwossen Gebreyes and colleagues at Ohio State University in Columbus tested US pigs for antibodies – telltale signs of infection – to pathogens that can also affect humans. They found traces of Salmonella in 39 per cent of pigs raised in standard indoor pens and routinely given antibiotics, but in 54 per cent of organic pigs raised outdoors without the drugs (Foodborne Pathogens and Disease, vol 5, p 199).

This poses a dilemma, says Gebreyes: giving pigs routine antibiotics favours antibiotic-resistant bacteria, but not giving …