Zinc is an essential trace element for birds as a cofactor
in many enzymes and involved in protein synthesis,
carbohydrate and energy metabolism, and other biochemical
reactions. Among other processes, it plays a
role in DNA and RNA synthesis, tissue growth and
repair, bone mineralization, and blood clotting (as reviewed
by Salim et al., 2008). Due to its central role, a
zinc deficiency will cause numerous physical and pathological
changes including skin lesions, decreased growth,
general disability of bones and joints, poor feathering,
and reduced immunity to infection of several diseases.
Zinc requirement of chicks was first defined to be 30
mg/kg of feed (Roberson and Schaible, 1958). Since
then, research provided new evidence for the NRC
(1994) to set the requirement of broilers at 40 mg/
kg of feed. As summarized by Salim et al. (2008), zinc
supplementation up to a level of about 30 to 50 mg of
Zn/kg of feed mainly increased feed intake and weight
gain and improved feed efficiency, whereas effects of
higher levels of Zn in the diet were less consistent.