Zinc is an important essential nutrient that is required in the bird’s diet. It is an essential component of both DNA and RNA enzymes with there also being an additional 200 zinc-dependent enzymes in the body. It is vital to the activity of a variety of hormones including growth hormone and sex hormones and it also plays a key role in stimulating the immune system. Adequate dietary zinc supplementation is critical in poultry production as a deficiency can have a serious impact.
Zinc is primarily absorbed in the small intestine and requires other dietary ingredients to ‘bind’ with it to allow it to be absorbed and to influence the bioavailability of the zinc. Bioavailability is affect by the presence of dietary calcium, magnesium, phosphorus, copper and iron. Zinc absorption though can be decreased in monogastric animals due to the presence, for example, of phytate.
Signs of zinc deficiency in young chicks include:
Although, in ageing hens zinc deficiency can reduce egg production, the most striking effects are seen in developing embryos. Chicks hatched from zinc-deficient hens are weak and cannot stand, eat, or drink. They have laboured breathing and accelerated respiratory rates which worsen when disturbed and often results in the death of the chick.
The major defect seen in hatched chicks is grossly impaired skeletal development. Zinc-deficient embryos show curvature of the spine, and shortened, fused thoracic and lumbar vertebrae. Often toes are missing and, in extreme cases, the embryos have no lower skeleton or limbs. Occasionally the eyes of some embryos are absent or not developed.
Feeding highly bioavailable sources of zinc, such as zinc complexes, to broilers has been known to show improvements in weight gain and feed conversion. It also has positive effects on egg production and shell quality in laying hens. Some feed ingredients can have low zinc content with varying levels of bioavailability so it may be necessary to add zinc to the poultry diet.