Trace mineral assessment in practice

摘要

Providing proper trace mineral nutrition in animals involves an important balancing act. Many factors must be reconciled to be sure that the essential needs for optimal production and performance are met without upsetting the balances of other nutritional elements or poisoning the animal. Those factors include other nutritional constituents, species and production class of the animal to be fed, type of feed involved, and essential requirements of the trace mineral involved. As with any clinical case, assessment of the mineral status of an animal or herd involves inputs from a variety of sources, including clinical history, clinical signs, clinical pathology, pathology (if animals have been lost), analytical chemistry, and bioassay. Unfortunately,no one source alone will provide the entire answer to a problem. This is especially true with trace mineral imbalances since deficiencies (in particular) are often manifested in terms of increased incidence of other, possibly common, diseases. Historically, a trace mineral deficiency may cause an outbreak of nutritional disease (e.g. white muscle disease in horses or cattle), or may be disguised by other concurrent diseases. The latter occurs with more subtle deficiencies of minerals such as selenium, copper, and zinc especially since those minerals are closely tied to proper immune function. Poisoning often is suggested historically when a feed or environmental change coincides with the onset of specific disease. The onset of disease could be delayedor happen after a period of accumulation in some cases, such as with the buildup of copper, followed by sudden and catastrophic losses of animals. In some instances, such as when molybdenum is present in excess, the signs of disease may be a deficiency of another metal, copper. When investigating a possible trace mineral problem, one may identify errors in supplementation, that may lead to either undersupplementation and deficiency, or oversupplementation and toxicosis. Overdosing of animals with a given element(s) have resulted from errors at all stages of formulation, mixing, and delivery. Misguided articles have encouraged farmers to add extra mineral to some rations as sort of the old "more is always better" attitude with disastrous results. Even if the ration is properly prescribed by the rancher or the nutritionist, transcription errors may lead to improper formulas leading to either toxicosis or deficiency. Once prescribed, it is then incumbent on the mill to properly mix the material, which hopefully arrived at the mill in the proper levels in the first place. Once mixed, a ration must be properly labeled. If not a total mixed ration, then those on the ranch must be sure that the total ration is balanced for each mineral as they provide the feed. Important decisions made at that level may include: How to best supplement? Which route to use? Is the feed best? How long will the product persist? Is overdosage possible? And other questions.