Trace mineral nutrition has a rich history of discovery and research in the field of poultry nutrition. Many of the early basic nutrient metabolism studies were conducted in chicks and then related to other livestock species and humans. The bulk of this work was conducted and reported in the era from 1960-1980. Nutrient requirements were established for each species of poultry and functions of those nutrients – trace minerals were also researched and reported. More recently, in the past 25 years, trace minerals’ role in immune function and related physiological roles have been studied. New organic sources of trace minerals have been patented and marketed providing a more available form of trace minerals for the chicken or turkey.
The complexity of trace mineral nutrition requires a thorough review of functions, interactions and availability of sources from time to time by the poultry producer/nutritionist.
The trace minerals of primary concern in poultry diets and having recommended levels of supplementation by the NRC (1994) Nutrient Requirements of Poultry include Zinc (Zn), Manganese (Mn), Copper (Cu), Iron (Fe), Selenium (Se) and Iodine (I). The trace minerals typically supplemented in poultry premixes include Zn, Mn, Cu, Fe and I. Selenium is very often supplemented either in the premix or separate from the premix formulation. Trace mineral premixes should be formulated and supplemented to poultry feeds separate from the vitamin premix due to potential vitamin oxidation by the trace minerals. Inclusion levels are often very small, ranging from .05 to .50 percent which means that weighing (scales) needs to be quite accurate and mixing needs to be thorough for the trace mineral premix to be adequately distributed in a batch of poultry feed.
Functions of Trace Minerals
Zinc plays an important role in poultry, particularly for layers, as a component of a number of metalloenzymes such as carbonic anhydrase which is essential for eggshell formation in the hens shell gland. Other important zinc metalloenzymes in the hen include carboxypeptidases and DNA polymerases. These enzymes play important roles in the hen’s immune response, in skin and wound healing, and for hormone production (testosterone and corticosteroids). Classic deficiency symptoms of a zinc deficiency in poultry could include a suppressed immune system, poor feathering and dermatitis, infertility and poor shell quality.
Copper also plays an important role in a number of enzyme functions in the bird. Copper is closely associated with iron metabolism as it is a part of ceruloplasmin which is an enzyme that plays an important role in the oxidation of ferrous to ferric iron, controlling the movement of iron from the reticuloendothelium to liver and then plasma, affecting red blood cell formation. A copper deficiency can cause microcytic hypochromic anemia. Another important enzyme dependent on copper is lysyl oxidase which is an integral enzyme in elastin and collagen formation in birds. A deficiency of copper can cause bone abnormalities due to abnormal collagen synthesis. Tibial dyschondroplasia is an example of a leg disorder in poultry that can be caused by a copper deficiency. Poor collagen and/or elastin formation can also lead to cardiovascular lesions and aortic ruptures. Copper is also important for feather development as well as feather color via its role in disulfide bond formation.
Iron has a very specific function in all animals as a component of the protein heme found in the red blood cell’s protein hemoglobin and in the muscle cell’s protein myoglobin. Iron has a rapid turnover rate in the chicken – 10 times per day – so it must be provided in a highly available form in the bird’s diet on a daily basis. Any internal infection such as coccidiosis can also interfere with iron absorption and availability. Iron deficiency can result in microcytic, hypochromic anemia in poultry.
Manganese plays a significant role in the chicken’s body in the formation of chondroitin sulfate. This mucopolysaccharide is an important component of bone cartilage. Deficiencies of manganese in poultry will result in perosis, bone shortening and bowing and in poor eggshell quality in laying hens.
Selenium is a very unique trace mineral in the chicken’s diet in that its inclusion rate is regulated and limited by the FDA. Selenium is considered a heavy metal in manure and is limited in its soil application. Selenium was recognized for its toxicity in animal diets before its essentiality was established. Selenium is an important constituent of the enzyme glutathione peroxidase which functions in the cell as its first line of defense against oxidation. Other selenoproteins in poultry play an important role in the prevention of exudative diathesis, normal pancreatic function, and fertility. Levels of selenium supplementation are limited by the FDA to only .30 ppm in poultry diets.
Levels of selenium in feedstuffs for poultry can vary considerably dependent on soil content of selenium the crops are grown on. Soils in the Dakotas and Canada can contain high levels of selenium resulting in higher grain levels of selenium. Often times, total selenium of poultry diets in our plains states will reach levels of .40 to .50 ppm when corn and soybean levels are combined with .30 ppm supplementation levels. These high levels can to be beneficial to the immune status and performance of poultry flocks without being toxic. Dietary selenium works with Vitamin E in boosting the immune status of poultry.
A number of negative interactions can occur such that an excess of one trace mineral will interfere with another trace mineral’s availability. The most common antagonism occurs between zinc and copper. High levels of dietary zinc will inhibit copper absorption, hepatic accumulation and deposition in the egg. Ratios greater than 4:1 of zinc:copper can be considered antagonistic. High levels of copper and iron can interfere with zinc availability and potentially could induce anemia. Excess dietary phosphorus will interfere with manganese availability in poultry.
Environmental factors such as water, equipment and/or soil conditions for crops may also contribute to a birds exposure to excessive trace minerals. Many soils in the Midwest have an abundance of manganese and zinc which can correspond to sometimes higher levels in the corn grown on these soils as well as high drinking water levels of some of the trace minerals. All of these potential sources need to be accounted for when calculating the birds’ consumption rate of trace minerals.
With new research being published showing improved utilization of organic trace minerals, the poultry nutritionist has to contemplate the validity of the NRC Nutrient Requirements of Poultry (1994) and how one can formulate rations more responsibly using organic trace minerals. With the stress to reduce flow of waste nutrients into the environment, poultry producers may be able to reduce overall supplementation of trace minerals, yet still receive optimum performance when using organic trace elements. Edited version of presentation given at the 2006 Midwest Poultry Federation Convention – Nutrition Symposium.