Trace minerals and the importance of bioavailability
When comparing different trace element sources, it is crucial to consider bioavailability. Also, there is a fresh look at chromium.
Trace minerals are an important part of poultry feeds as they play crucial roles in growth and production. It is not only the quantity of mineral present in feed but also its bioavailability that determine the effectiveness of the trace mineral product. Knowledge of the bioavailability of trace minerals from different sources is important for economic feed formulation and to maintain or even improve flock performance.
Types of minerals
Minerals may be divided into two categories, based on the amount that is required in the diet. Requirements for major or macro minerals are usually given as a percentage of the diet, whereas requirements for minor or trace minerals is stated as milligrammes per kilogramme (mg/kg) or parts per million (ppm).
The requirements for the major minerals, e.g. calcium, phosphorus, sodium and chlorine, are often met by the contribution from the feed ingredients and mineral supplements, such as dicalcium phosphate and salt. On the other hand, trace minerals, e.g. manganese, zinc, iron, copper, iodine, cobalt, selenium, chromium, are added as trace mineral mixture or premix, ignoring the contribution from the feed ingredients. Table 1 lists the most important trace mineral and typical symptoms of deficiency in poultry.
Importance of bioavailability
Bioavailability of trace minerals determines efficacy. In most cases, supplemental trace minerals are supplied through inorganic sources. Although some new organic sources have been introduced in recent years, inorganic sources of trace minerals, including sulphates and oxides, are still most widely used in animal feeds.
Sulphate salts of trace minerals are the most bioavailable (100%) of inorganic salts, while the bioavailability of oxide forms is usually the lowest. Sulphate salts provide complete bioavailability of trace minerals, resulting in better flock performance. In contrast, most of the mineral from oxide salts is lost because of poor bioavailability.
However, the content of the elemental mineral tends to be higher in oxide salts than sulphate salts. Therefore, to get a certain quantity of elemental mineral, less of the oxide salt is required than, for example, the sulphate salt.
This explains why a trace mineral premix containing oxide salts can be given at a lower mixing rate (e.g. 500g per tonne of feed) than one containing sulphate salts (e.g. 1 kg per tonne of feed). More of the raw material is required to provide the same amount of elemental minerals. An example calculation is shown in Table 2. The table demonstrates that in order to provide total 140g of elemental minerals as mentioned in row 1, 611g of sulphate salts or 246g of oxide salts is required.
Of course, a trace mineral mix may also contain other elements, e.g. iodine, cobalt, or selenium. The premix product may also include a stabiliser and/or carrier. All of these add to the weight of the trace element mixture in the finished feed.
Although the total elemental mineral content in 246g oxide salts and 611g sulphate salts is the same in this example, the total bio-available mineral is only 67g from the oxide salts against 140g from the sulphate salts. Because sulphate salts provide complete bioavailability of trace minerals, they result in better flock performance.
Many trace mineral products on the market do not reveal information about the salts although the recommended mixing rates may give a clue to the type of salts included. It is important for nutritionists to be aware of the significant differences in useful' or bioavailable trace mineral content from different products and suppliers.
Chromium: essential for energy metabolism
Poultry feed needs to supply energy, and efficient energy utilisation results in higher productivity. Chromium is an essential element required for normal metabolism of carbohydrates, proteins and lipids.
Glucose, produced from carbohydrates, is the major source of energy. Insulin takes a major part in the glucose metabolism. Chromium acts biologically as a component of glucose tolerance factor (GTF). GTF enhances tissue sensitivity to insulin and glucose utilisation.
As feed prices rise, poultry nutritionists and producers should consider including chromium in the feed in order to maximise the all-important margin over feed costs.