Trace elements are nutrition elements that occupy a very small share in the feed but are not available. However, because the share is too small, they are often ignored. Trace elements play a key role in the growth and reproduction of pigs. The amount of additions will be discussed with everyone.
This article contains the following:
Trace element requirements
Trace element requirements are difficult to determine, and most estimates are based on the minimum levels needed to prevent symptoms of deficiency. Most studies related to trace element requirements were conducted in the 1960s and 1970s and may not be applicable to modern animals. With a few exceptions, the amount suggested by NRC (1998) is only slightly different from that suggested by NRC (1988) or ARC (1981) (Table 1). Therefore, there is a lack of information on the trace element requirements of modern pig genotypes. Van Lunen et al. (1998) proposed that modern fast-growing pigs require about twice as many trace elements as pigs that grew slowly 20 to 30 years ago.
Trace element allowable
Due to concerns about the effects of trace elements on animal nutrition, the levels of trace elements added to diets often exceed the "recommended requirements". However, excessive addition can also cause toxicity or residue, and the excretion of some extra trace elements to the outside will pollute the environment, so the maximum allowable intake (UL) needs to be determined. At present, the method of determining the maximum safe intake according to the UL value (UL method) has become an international standard. Factors such as the type of animal, its performance level, and the source and utilization of trace elements should be considered when determining UL. Whittemore et al. (2002) investigated the allowable amounts commonly used in some EU countries (Table 2), and the survey results showed that the content levels were quite different, and some were even 3 to 4 times higher than the recommended amounts in Table 1. These are to ensure good performance and meet the needs of animals under different production and management methods, as well as to improve immunity and health.
In determining trace element additives, the type and quantity of raw materials, the processing, storage and environmental conditions of the diet, and other trace elements and content must be considered. One of the most convincing examples is that copper, zinc, and iron can interact. If Cu is used as a growth promoter, the demand for Zn and Fe will increase. Stranks et al. (1988) suggested that the level of Cu in the diet should be 175 mg / kg, the level of Fe should be increased to 200 mg / kg, and that of Zn should be increased to 150 mg / kg. These values are higher than those recommended in many national standards and may explain why higher than the maximum allowable practice is often used in commercial feeding activities.
Trace element sources and bioavailability
Trace element sources and bioavailabilityIn general, the addition of inorganic salts such as sulfates, carbonates, chlorides and oxides to the diet provides the appropriate level of trace elements to meet the needs of the animal. Free ions and absorbed. However, free ions are very active and can complex with other dietary molecules and the complexes formed are difficult to absorb. Animal use of trace elements also varies widely. Under extreme conditions, trace elements may not be absorbed and used, which limits their beneficial effects on animals. A large amount of undigested and absorbed trace elements are discharged from the body and cause environmental pollution. Therefore, it is important to understand the bioavailability of trace elements.
Because there is no big difference in the bioavailability of Zn from different inorganic sources, this means that 75% to 80% of the Zn intake is excreted by animals. People are paying more and more attention to trace elements in organic forms such as protein complexes or chelates. This form of trace elements is the chemical combination of trace elements with chelating agents or ligands, which is usually combined with amino acids or small molecule peptides to make Has higher bioavailability and biological activity. This form of trace elements can be added at relatively low levels without harming the performance of the animal, and thus minimizing the excretion of trace elements and their impact on the environment. At present, the commercial organic trace elements are mainly chelates or complexes composed of cations and anionic or neutral complexes (also called ligands).
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