The Ability of Chickens to Select Nutritive and Avoid Toxic Concentrations of Heavy Metals in Feeds

The ability of free range chickens to detect and select feeds with varying heavy metal concentrations is important in relation to their ability to avoid toxic heavy metals in polluted regions and to self-supplement their diet with nutritive metals. An operant test was conducted to determine whether chickens could detect a range of heavy metals mixed with feed pellets, with seven birds rewarded for selecting feeds with added metals and seven birds rewarded for selecting feeds without added metals. The chickens demonstrated an ability to detect very high levels of iron, copper, and zinc in feed, but they could not detect concentrations typical of polluted regions, that is, 1,500-2,000 mg/kg feed. They also Could not detect the potentially toxic elements cadmium, lead, or selenium at concentrations Just below the level likely to induce toxicity. The chickens were successfully trained to discriminate between three different pairs of colored plates (red/green, black/yellow, and blue/white) and to associate the different pairs of colored plates with food contaminated and uncontaminated with copper, zinc, and iron, respectively, at the maximum concentration which they could detect. Their preference for the contaminated or uncontaminated food samples was then investigated ability and the second preferences. The second method could not have been used to determine discrimination ability, or at least it would have been unnecessary and potentially confusing to involve a colour association. The first method could not easily have been used to determine preferences, because the color association allowed the birds to choose one or other arm of the Y maze before they reached the point of no return. Hence, the method allowed a voluntary choice to be made in the easiest way. Colour association has been used to test chickens' nutritional preferences previously (e.g., Kutlu and Forbes, 1993).