Minerals can be divided into two main catergories, 1) macro-minerals and 2) micro or trace minerals. Macro minerals are minerals that are needed in relatively large amounts in comparison to trace minerals (or micro minerals) which are needed in relatively small amounts. In general, macro minerals such as phosphorous, potassium, sulphur, magnesium, sodium and chloride and trace elements such as copper, zinc, cobalt, iodine, manganese, selenium, cobalt and iron are considered essential for cattle (NRC,1996). Consequently, their deficiencies or imbalances in soils and forages have been long held to be responsible for low production and also reproduction problems among grazing animals ( McDowell, 1985).
Macro minerals have important physiological functions in livestock and must be supplemented to livestock diets when forages or rations are deficient- or have the incorrect proportions of macro minerals. If these minerals are not supplied in correct amounts metabolic diseases or toxicities can occur.
In addition, it is important to note that physiological imbalances commonly observed in cattle livestock are due to deficiency in trace minerals, for in order to promote normal tissue growth, that is, homeostasis, enzyme function, cell regulation and immune function, it is of great importance that trace elements be maintained within narrow concentrations in the body (McDowell, 1989, 1992; Underwood and Suttle, 1999).
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In the tropics, mineral imbalances in soils and forages, whether deficient or in excess, have been held responsible for low production and reproductive problems among grazing cattle.. After much investigation, forage animals grown on tropical soils were found to be highly deficient in a number of macronutrients and trace elements. , Consequently, it has become necessary to provide these elements, as dietary supplements, in order to promote efficient and profitable livestock production in warm climate regions.
Historically, in the early 1800s, in tropical countries , the mineral constituents of plants were shown to vary with soil type and stages of maturity of forages. The outcome was that under-nutrition was commonly accepted as one of the most significant limitations to grazing cattle production and the consequent lack of sufficient energy and protein were often responsible for suboptimum livestock production.
One of the reasons for the lack of supply of these important macro and micro minerals in food for cattle was that, before the middle of the 19th century, only the most unformulated ideas existed as to the nature, origin and function of minerals for both plant and animals (McDowell, 2003). It is only when methods were devised to identify and measure mineral constituents in animal body tissues and feeds, and ways and means used to characterize these animals' responses to single elements, was it possible to replace assumptions with facts about the makeup of these elements. Thus even as late as the early 1900s and into the 20th century, it can be stated that little attention was given to mineral nutrition of cattle, since this form of nutrition for cattle was treated as being of little importance (Ammerman and Goodrich, 1983).
Factors affecting trace element requirements
The involvement of trace elements in animal production and disease resistance and deficiencies have not always reduced performance or increase the susceptibility of livestock to natural or experimentally reduced infections (Spears, 2000). There are many factors that could affect response to trace mineral supplementation. They are duration, form and concentration of supplementation, physiological status of an animal (pregnant vs non pregnant), the absence or presence of dietary antagonists, environmental factors and the influence of stress on trace mineral metabolism.
Although species differences in trace mineral metabolism have long been recognized, only recently have differences been noted between breeds within a species. Differences in trace mineral metabolism between breeds of cattle have been reported. In an experiment by Du et al. (1996), Holstein (n=8) and Jersey (n=8) primiparous cows and Holstein (n=8) and Jersey (n=8) growing heifers were supplemented with either 5 or 80 mg of copper/kg dry matter for 60 days. At the end of the experiment, Jerseys had higher liver copper concentrations relative to Holsteins across treatments. Also, liver copper concentrations increased more rapidly and were higher in the Jerseys supplemented with 80 mg of copper/kg DM compared to Holsteins supplemented with 80 mg of copper/kg DM by day 60 of the experiment. Overall serum ceruloplasmin oxidase activity (a copper-dependent enzyme involved in iron transport) was higher in Jerseys than Holsteins. in addition, Jersey cows and heifers had higher liver iron and lower liver zinc concentrations than did Holstein cows and heifers at day 60 of the experiment. This data indicate that Jerseys and Holsteins metabolize copper, zinc, and iron differently.
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Ward et al. (1995) conducted a study in which Angus (n=8) and Simmental (n=8) steers were placed in metabolism crates to monitor apparent absorption and retention of copper. At the end of the six-day experiment, plasma copper concentrations, apparent absorption and retention of copper were higher in Angus comparative to Simmental steers. The writers indicated, from their data as well as from others, that Simmental cattle may have a higher copper requirement than Angus cattle and that these different requirements may be related to differences in copper absorption from the gastrointestinal tract between breeds. In addition, it has also been suggested that these breed differences in copper metabolism may not be due solely to differences in absorption, but also to the manner in which copper is utilized or metabolized post-absorption. Gooneratne et al. (1994) reported that biliary copper concentrations are considerably higher in Simmental cattle than in Angus cattle. It is apparent that differences in copper metabolism exist between Simmental and Angus cattle both at the absorptive and post-absorptive level.
Another study comparing the mineral status of Angus, Braunvieh, Charolais, Gelbvieh, Hereford, Limousin, Red Poll, Pinzgauer and Simmental breeds consuming similar diets has also been conducted (Littledike et al., 1995). This study compared not only copper, but also zinc and iron status between the mentioned breeds of cattle. In adult cattle, it was shown that Limousin liver copper concentrations were higher than all other breeds, except for Angus. This same trend was not seen for zinc or iron, with very little breed differences observed. Serum zinc and copper concentrations did not differ by breed.
Several experiments have been conducted using lab animals and humans that indicate trace mineral metabolism is altered during pregnancy. Research has indicated that zinc concentrations increase in bovine conception products (placenta, placental fluids, and fetus) as the fetus grows (Hansard et al., 1968). Studies using rats have shown that the overall maternal body stores of copper and zinc increase during pregnancy and then decrease during lactation. Mean zinc total body stores at the start of pregnancy were recorded at 5260 mg of zinc versus 5810 mg of zinc at day 15 of pregnancy. By day 14 of lactation, maternal body stores of zinc had decreased to 5640 mg of zinc, which was still considerably higher than at the onset of pregnancy (Williams et al., 1977). These same trends were observed with copper. In a more recent experiment by Vierboom et al. (2002), pregnant cows and sheep absorbed and retained zinc to a greater degree that non-pregnant cows and sheep. This data indicated that certain physiological and metabolic parameters are altered in pregnant cows and ewes consuming an alfalfa-based diet that enhance the apparent absorption and retention of certain trace minerals.
The abovementioned data indicate that copper and zinc metabolism is altered in pregnant vs non- pregnant animals. Further research is required to determine the metabolic mechanisms that enable pregnant animals to alter copper and zinc metabolism as well as the animal's specific metabolic requirement for both maintenance and fetal development. In addition, research is needed to determine the effects of gestational status on the metabolism of other trace minerals, as well as if breed differences exist relative to trace mineral metabolism and gestational status
As mentioned earlier, trace minerals such as copper and zinc are involved in immune response. Deficiencies and or imbalances of these elements can alter the activity of certain enzymes and function of specific organs, thus impairing specific metabolic pathways as well as overall immune function. Stress and its relationship to the occurrence of disease hav long been recognized. Stress is the nonspecific response of the body to any demand made upon it (Selye, 1973). Stress factors relative to animal production include a variety of circumstances such as infection, environmental factors, parturition, lactation, weaning, transport, and handling. Stress induced by parturition, lactation, weaning, and transport has been shown to decrease the ability of the animal to respond immunologically to antigens that they encounter. Also, research has indicated that stress can alter the metabolism of trace minerals. Stress in the form of mastitis and ketosis has been shown to alter zinc metabolism in dairy cattle. Orr et al. (1990) reported an increase in urinary copper and zinc excretion in cattle inoculated with IBRV. Furthermore, Nockels et al. (1993) reported that copper and zinc retention was decreased in steers injected with ACTH (a stressor) in conjunction with feed and water restriction. These studies, in conjunction with several others, indicate that stress in the form of an infection (IBRV), a metabolic disorder (ketosis), or deprivation of feed and water can increase copper and zinc reduction
TRACE MINERAL ANTAGONISTS
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Many element-element interactions have been documented. These include zinc-iron, copper-iron, copper-sulfur, copper-molybdenum, and copper-molybdenum- sulfur interactions and interactions between elements and other dietary components. Peres et al. (2001) used perfused jejunal loops of normal rats to characterize the effects of the iron:zinc ratio in the diet on mineral absorption. When the iron:zinc ratio in the diet was held below 2:1, no detrimental effects on absorption were observed. However, once concentrations were increased to a ratio between 2:1 and 5:1, zinc absorption was decreased. Similar effects have also been seen for copper absorption, with depressed copper uptake in the presence of excess iron (Phillippo et al., 1987). The best known mineral interaction that can cause a reduction in copper absorption and utilization is the copper-molybdenum-sulfur interaction. On the other hand, even molybdenum or sulfur alone can have antagonistic effects on copper absorption. Suttle (1974) reported that plasma copper concentrations were reduced in sheep with increasing concentrations of dietary sulfur from either an organic (methionine) or inorganic (sodium sulfate) form. In another experiment, Suttle (1975) demonstrated that hypocupraemic ewes fed copper at a rate of 6 mg copper/kg of diet DM with additional sulfur or molybdenum, exhibited slower repletion rates than sheep fed no molybdenum or sulfur. However, when both molybdenum and sulfur were fed together, copper absorption and retention was drastically reduced. Current research would support these findings and suggest that in addition to independent copper-sulfur and copper- molybdenum interactions, there is a three way copper-sulfur-molybdenum interaction that renders these elements unavailable for absorption and metabolism due to the formation of thiomolybdates (Suttle, 1991).
Ward (1978) also investigated the independent effect of molybdenum on copper absorption and concluded that elevated molybdenum intake reduces copper availability and can lead to a physiological copper deficiency. Based on this and previous experiments, it appears that the ratio of the antagonistic elements seems to be more important than the actual amounts. Miltimore and Mason (1971) reported that if copper: molybdenum ratios fall below 2:1, copper deficiency can be produced. Therefore, feeding additional copper has been recommended in areas where a molybdenum interaction is suspected. Huisingh et al. (1973) further concluded, in their attempt to produce a working model of the effects of sulfur and molybdenum on copper absorption, that both sulfur (in the form of sulfate or sulfur-containing amino acids) and molybdenum reduce copper absorption due to the formation of insoluble complexes. They also noted that sulfur and molybdenum interact independently and suggested that they may share a common transport mechanism.
Interactions between and among minerals are not the only possible inhibitors of mineral absorption. Other dietary components can also inhibit or enhance the amount of mineral that is absorbed. Protein, as might be expected from the discussion involving sulfur-containing amino acids, is an example of a dietary component that can affect mineral metabolism. Snedeker and Greger (1983) reported that high protein diets significantly increase apparent zinc retention. In contrast, diets high in sulfur- containing amino acids have been shown to decrease copper absorption, most likely due to the formation of insoluble copper-sulfur and potentially copper-sulfur-molybdenum complexes (Robbin and baker 1980)
O'Dell (1984) noted the potential for carbohydrate source to affect copper absorption. This was attributed to phytate as well as oxalate concen- trations in the diet. Fiber can also act as a mineral trap due to its relatively negative charge, which serves to bind the positively charged divalent metal cations rendering them unavailable for absorption (van der Aar et al., 1983).
Age has also been shown to alter trace mineral needs. Trace mineral requirements have been reported to vary with age of dairy cattle (NRC, 2001). Wegner et al. (1972) reported that dairy cattle in their second to fifth lactations had higher serum zinc concentrations than either first lactation or bred heifers, 131 mg/100 ml, 85 mg/100 ml and 93 mg/100 ml respectively. This change in mineral needs over time is most obvious in young, growing animals.
The general functions of minerals can be broken down into four categories: 1) structural: minerals that play a role as components of tissues; 2) physiological: minerals that are involved in acid-base balance; 3) catalytic: minerals that are components of enzyme and hormone systems; and 4) regulatory: minerals that are involved in cell replication processes, (Underwood and Suttle, 1999).
The necessity of copper for cattle was first established in the 1930's with the discovery in Florida that cattle had a wasting disease were deficient in cobalt, iron and copper. Researchers in Northern Europe described the wasting disease by animals as having diarrhea, loss of appetite and anemia (McDowell, 1992).
Copper is second only to zinc in the number of enzymes that require it for appropriate function
(Underwood and Suttle, 1999). Copper is therefore essential to proper physiological function and is involved in an range of systems. These include iron metabolism, cellular respiration, cross-linking of connective tissue, central nervous system formation, reproduction and immunity as well as several other functions. (McDowell, 1992).
In order for hemoglobin synthesis to occur, iron must be converted to the ferric form before being incorporated into the hemoglobin molecule. This process is accomplished by ceruloplasmin, which is a copper-containing enzyme synthesized in the liver for this purpose (Saenko et al., 1994). Therefore, in a state of copper deficiency, hemoglobin synthesis is reduced (Hart et al., 1928). Copper is also an essential component in the enzyme cytochrome oxidase. This enzyme acts as the terminal oxidase in the electron transport chain and is essential to cellular respiration by converting oxygen to water (Spears, 1999). Cytochrome oxidase is also necessary for proper central nervous system function. Enzootic ataxia (swayback), which is associated with incomplete myelin formation, has been linked to an observed decrease in cytochrome oxidase activity in young lambs (Fell et al., 1965). Cross-linking of connective tissue is also facilitated by a copper containing enzyme, lysyl oxidase (Harris and O'Dell, 1974). In the absence of lysyl oxidase, dehydromerodesmosine cannot be converted to isodesmosine, which is an essential component in the cross-linking of elastin (Gallopet al., 1972).
The essentiality of copper for optimal reproductive performance has also been widely documented, although a specific copper-linked enzyme that is responsible has not been identified. It is likely that a group of copper-containing, or copper-activated, compounds is involved in the reproductive process making this identification even more difficult. Corah and Ives (1991) noted that clinical signs of copper deficiency associated with reproduction include decreased conception rate, overall infertility, anestrus and fetal resorption. Some of these problems may be associated with the function of a major intracellular enzyme, copper-zinc superoxide dismutase. This copper-containing enzyme functions as an antioxidant to protect cellular contents from oxidative stress. The same copper-zinc superoxide dismutase has also been implicated to have an important role in proper function of the immune system (Miller et al., 1979).
The highest concentration of zinc were found in the following order: pancreas, liver, pituary gland, kidney, and adrenal gland (McDowell, 1992).Zinc is also involved in an array of other systems as an enzyme component or activator. It therefore plays an indirect role in gene expression, growth, reproduction, immunity, vitamin A metabolism and many other processes (McDowell, 1992). Chesters (1997) indicated that zinc is involved as a component of a number of transcriptional regulators involved in the gene transcription process. Involvement in the basic transcription process may be the main role that zinc plays across all body systems, although it is not the only area of zinc influence.
Zinc has been shown to be essential for adequate growth and development. However, reduction in growth rate may partly be due to a decreased feed intake that has been observed in conjunction with zinc deficiency in rodent models (Mills and Chesters, 1969). Spears (1999) has suggested that poor growth may also be correlated with a reduction in protein synthesis due to impaired gene transcription processes under conditions of zinc deficiency. Reproduction has been identified as an area that is significantly affected by a state of zinc deficiency.
In the 1960's scientist discovered that a skin disorder of cattle could be cured with zinc therapy. Additional clinical signs of a zinc deficiency include inflammation of the nose and mouth with submucous haemorrhages, unthrifty appearance, rough hair coats, stiffness of the joints with swelling of the feet and fetlocks, cracks in skin of coronary bands around the hoves and dry scaly skin on the ears (McDowell, 1992).
Manganese is involved in many of the same processes already mentioned for zinc and copper, although the original research that identified manganese as an essential trace element was based on measurements of reproductive parameters (Orent and McCollum, 1931; Kemmerer et al., 1931). Hidiroglou (1975) showed that manganese uptake was greater in the ovine Graafian follicle and corpus luteum when compared to other reproductive tissues. This research suggested that manganese may be essential for normal ovarian function. As Maas (1987) pointed out, manganese deficiency has been associated with the anestrus condition in cattle as well. Manganese has also been identified as a component of manganese superoxide dismutase, which functions in a similar manner to copper-zinc superoxide dismutase by reducing the risk of peroxidation damage to body tissues, particularly the heart (Malecki and Greger, 1996). Manganese has also been identified as an essential component in bone and cartilage formation and growth. Leach (1971) noted that manganese is essential in the activation of glycotranferases that are partly responsible for mucopolysaccharide synthesis. Without these important structural components of cartilage, skeletal defects often result. Manganese is also involved in lipid and carbohydrate metabolism. Therefore, manganese deficiency can potentially lead to a decrease in overall animal growth (Prasad, 1984).
McDowell (1992) and Underwood and Suttle (1999) have also identified manganese as an essential component for brain function, structural integrity of cells, enzyme activity and most interestingly, blood clotting. Doisey (1973) showed that manganese-deficient chicks exhibit a reduction in the blood clotting response
Selenium was first identified in the 1930s as a toxic element to some plants and animals. However, selenium is now known to be required by laboratory animals, food animals, and humans (McDowell, 1992). Selenium is necessary for growth and fertility in animals and for the prevention of a variety of disease conditions. In 1973, Rotruck et al. reported that selenium functions as a component of glutathione peroxidase (GSH-Px), an enzyme that inactivates oxygen radicals such as hydrogen peroxide and prevents them from causing cellular damage. Since the discovery by Rotruck et al. (1973), selenium has been shown to affect specific components of the immune system (Mulhern et al., 1985). Earlier research by Reffett et al. (1988) reported lower serum IgM (an antibody produced by B-cells) concentrations and anti-IBRV titers in selenium-deficient calves challenged with infectious bovine rhinotrachetis virus than when compared to selenium-adequate calves. Polymorphonuclear leukocyte function was reduced in goats (Azizi et al., 1984) and cattle (Gyang et al.,1984) fed selenium-deficient diets compared with controls receiving selenium-adequate diets. Some studies have shown increased T-lymphocyte blastogenesis following in vitro stimulation with mitogen while others have not (Spears, 2000). Recently, bovine mammary endothelial cells growing in selenium- deficient cell culture media were found to exhibit enhanced neutrophil adherence when stimulated with cytokines (Maddoxet al., 1999; Spears, 2000). These findings may indicate that selenium could affect neutrophil migration into tissues and subsequent inflammation.