The Absorption of Copper and Zinc by Cattle Consuming Diets Containing the Antagonists Molybdenum, Sulfur, and Iron

By J.A. Paterson, C.K. Swenson, R.P. Ansotegui, B. Wellington, Department of Animal and Range Sciences Montana State University-Bozeman and A.B. Johnson, Zinpro Corporation, Minnesota

Introduction

Among the numerous management challenges that cattle producers face, one nutritional challenge is to satisfy the trace mineral requirements of the cow herd. As the genetic progress of the herd improves, mineral supplementation strategies become more complex and are influenced by a variety of factors, including forage mineral bioavailability, trace mineral interactions, stage of production and even breed. Adequate intake and balance are required for proper functioning of metabolic processes including immune response and reproduction. The trace elements most commonly identified as having an impact on productivity of cattle include copper, zinc, and selenium.

Trace mineral deficiencies can be classified as either primary or secondary. A primary deficiency is caused by inadequate dietary intake of one or more essential minerals while a secondary deficiency is caused by an interference in absorption, distribution or retention of a mineral. A preexisting disease or a mineral interaction can cause a secondary deficiency. Both deficiencies can occur simultaneously, making the evaluation of mineral status complex.

Trace Minerals: Copper & Zinc

Copper is an essential trace element required for enzyme systems, iron metabolism, connective tissue metabolism and mobilization, plus integrity of the central nervous and immune systems. Copper functions in the immune system through energy production, neutrophil activity and antioxidant enzyme production. It also aids development of antibodies and lymphocyte replication (30). Reproductive efficiency may be reduced when a Cu deficiency occurs because of metabolic alterations of enzyme systems.

Zinc is actively involved in enzyme systems through metabolism of protein and carbohydrates. Zinc is also required for maintaining responsiveness of the immune system through energy production, protein synthesis, stabilization of membranes against bacterial endotoxins, antioxidant enzyme production and maintenance of lymphocyte replication and antibody production (30). Virtually every phase of cell growth involves Zn, and a deficiency can impact productivity. For example, zinc serves as an activator of enzymes necessary in steroidogenesis, which regulates secretion of gonadal hormones.

Forage Levels

Forages provide the nutritional base of beef and dairy operations. Supplementation decisions pivot around both the quantity and quality of the forage base. In addition to protein and energy content of the feed resource, mineral concentrations must also be considered. The dietary requirements of various trace elements are presented in Table 1. Presented in Table 2 are results of a forage survey of 352 cow/calf producers across 18 states. The forages evaluated in this survey were placed in the following categories: alfalfa, brome, bermuda, fescue, sudan, cereal forages, native or prairie grass, grass (brome, timothy, mixed grasses and other grass/hay combinations), silage and other.

Results (Table 2) revealed a deficiency for Zn with only 2.5% of the analyzed forages having adequate levels (>30 ppm). Copper values indicated that 14.2% of the forages were deficient and 49.7% contained marginal levels. Iron and Mo levels in 10% of the forages were high enough to cause a Cu deficiency due to antagonistic affects on absorption. Forage Mn concentrations were at adequate levels in 76% of the samples.

Grings et al. (1992) evaluated mineral concentration of forage grasses in the Northern Great Plains and their adequacy to meet nutritional needs of grazing livestock. Phosphorous, zinc and copper were the minerals most likely to be considered deficient for cattle. Several studies (28, 42, 20 and 6) have reported mineral concentrations for range grasses in Montana and mineral values from all four studies were in agreement. Three of the studies were conducted at the same research site during winter grazing periods in 1986, 1987 and 1991. The similarity of values over the various years indicated little fluctuation of elemental values from year to year. Copper (3 ppm) and Zn (25 ppm) levels appeared to be deficient for meeting cattle requirements; however, Mn (79 ppm) was adequate (6).

Mineral analysis of forage samples determines concentration of specific elements; however, bio-availability to the animal is more difficult to measure. Release of minerals from the forage and interactions with microbial cells, other minerals, or other forage components in the rumen can influence availability for absorption by the animal (36).

Minerals in forage consist of three fractions: 1) highly soluble and rapidly released; 2) slow release as cell walls and protein components are degraded and, 3) no release. The major portion of Cu in forages appears to be contained in the rapid release fraction; however, Zn has been shown to have the lowest percentage release compared to Ca, Mg, K, P and Cu. Increasing the NDF content of the diet has also been shown to decrease apparent absorption of Mn, Zn, Fe, and Cu.

Interactions

Copper deficiency has been identified as a serious problem for grazing ruminants (1). A deficiency may be due to low concentrations of Cu in forage and can be further exaggerated when Mo, Fe and S levels are elevated.

Molybdenum and selenium interfere with Cu absorption by forming thiomolybdates that bind Cu, resulting in compounds that cannot be absorbed by the animal (17, 36). Decreased liver Cu levels can be caused by excessive Fe in the diet (4). In the same study, Mo appeared to have an additive action with Fe by decreasing liver Cu, while S and Fe had independent effects on Cu. The antagonistic mechanism of Fe is not well understood. It was suggested (38) that iron may form ferrous sulfide complexes in the rumen that solubilize in the abomasum, allowing the sulfide to dissociate and form insoluble complexes with copper.

Excessive dietary Zn can negatively effect Cu status through the absorption process (31, 12). Metallothionine concentrations in intestinal mucosa were induced by Zn, and the protein had a higher binding affinity with Cu than Zn. Fischer et al. (14) reported that bound Cu was sloughed off with mucosal cells rather than being absorbed. Activities of Cu metalloenzymes, heart and liver superoxide dismutase and cytochrome c oxidase, were depressed by high levels of dietary Zn (23, 14).

Immune system

Deficiencies of protein, energy, vitamins and minerals are known to compromise immune function (Beisel, 1982). Jones and Suttle (1983) showed that Cu-deficient mice had an increased susceptibility to experimental infections with Pasturella hemolytica. Wooliams et al. (1986) reported that lambs with low Cu status were vulnerable to bacterial infections while Xin et al. (1991) showed that neutrophils from dairy steers made Cu deficient by feeding 10 ppm molybdenum had a significantly lower capacity to kill S. aureus than neutrophils from Cu-supplemented animals.

Trace mineral deficiencies in beef cattle have been shown to alter various components of the immune system (39). Stabel et al. (1981) reported viral and bacterial challenges increased serum ceruloplasmin and plasma copper in copper-repleted cattle indicating a major protective role of copper in infectious diseases. Copper deficiency in ruminants resulted in decreased neutrophil function (22, 29) and altered acute-phase protein response to viral infection (3).

Gershwin et al. (1985) indicated that zinc had an indispensable role in the development and maintenance of immunocompetence. Zinc has been shown to have a positive impact on immunity in stocker and feeder cattle with limited research in beef cows. Zinc supplementation enhanced recovery rate in IBR-virus-stressed cattle (5). Zinc methionine has also been shown to increase antibody titer against bovine herpesvirus-1 (36).

Improved antibody titers for IBR-challenged yearling heifers when Cu, Zn, Mn and Co were supplemented, were reported (7). Supplementing first-calf gestating beef heifers with amino acid-complexed forms of Cu, Zn, Mn and Co enhanced cell-mediated immune response when compared to heifers supplemented with sulfate forms of the trace minerals or heifers offered supplement with no additional Cu, Zn, Mn , and Co (2).

Reproduction

Intake of bioavailable minerals is necessary in postpartum cows for proper involution of the uterus, display of estrus, ovulation, conception and maintenance of a new fetus. Doyle et al. (1988) reported a decrease in length of time from the beginning of the breeding season to conception for cows supplemented with trace minerals compared to cows fed supplement without trace minerals or those receiving no supplement. In a Cu deficient status, productivity may be reduced due to metabolic alterations of enzyme systems. Delayed or suppressed estrus and embryo death have been identified as common symptoms of Cu deficiency in beef cattle (21). Infertility associated with a Cu deficiency may also be a result of excessive dietary Mo intake. In a study reported by Phillippo et al.(32) heifers receiving a diet with marginal Cu levels and high Mo exhibited delayed puberty, lower ovulation rates and lower conception rates compared to heifers consuming a diet containing high levels of Fe.

Zinc deficiency can adversely affect reproductive processes in females from estrus to parturition (26). Inadequate Zn levels in gestating cows may result in abortion, fetal mummification, lower birth weight or altered myometrial contractility with prolonged labor. Maas (1987) reported impaired growth, delayed puberty and decreased appetite in Zn deficient bull calves. A loss of appetite results in lowered mineral ingestion, which further decreases feed utilization due to hindered nutrient metabolism.

Evaluating Mineral Status

Sub-clinical or marginal mineral deficiencies may have an economic impact on the beef producer. Trace mineral imbalances can be the result of dietary levels, water source, production demands, breed differences and mineral interactions. Sub-clinical trace mineral deficiencies in cattle may be a larger problem than an acute deficiency because specific clinical symptoms are not obvious enough to allow the producer to recognize a deficiency (46). Cattle with a sub-clinical status continue to reproduce or grow, but may have decreased feed efficiency and a depressed immune system.

Evaluating serum copper concentration has been a common practice to evaluate herd mineral status. However, not all copper circulating in the blood is available to the animal, and serum copper values can be affected by a number of factors including dietary Mo and sulfate consumption, infection, trauma and stage of gestation (33).

Work showed (8) that serum copper levels were not well correlated to liver copper, and are not considered a reliable indicator of copper status in cattle. Copper metabolism and variations in plasma Cu may be breed specific because it has been reported to have a heritable component (44). Differences were indicated (24) in liver and serum concentrations of Cu and Zn among breeds of cattle. Limousin had higher liver Cu levels than any of the other nine breeds, except Angus. In Saskatchewan, Cu deficiency occurred more frequently in Simmental cattle compared to other breeds (35).

Assessing Zn status is also difficult because at present there is no good indicator for determining marginal deficiencies. Given the complexity of determining mineral status in cattle due to interactions among minerals, variability of trace mineral levels in forage and bioavailability to the animal, dependence on a single variable of mineral status may result in an erroneous diagnosis.

Our recommendation to producers has been to start first with a forage analysis (Cu, Zn, Mn, Fe, S, Mo, Se), second with a water analysis (Fe, S), followed by serum sampling (Se) and a liver biopsy (Cu, Zn, and Mo).

Montana State University Research

Consumption of the complexed form of Cu (copper lysine) increased liver Cu levels in the presence of antagonists and maintained a higher Cu level approximately 150 d after supplementation had ceased (40). Heifers fed the complexed form of Zn (zinc methionine) had increased liver Zn levels within 30 d of supplementation and levels continued to be higher at breeding. However, Zn liver levels were similar among treatments after supplementation ended. Improved levels of liver Cu and Zn with complexed mineral forms may be a consideration for strategic trace mineral supplementation of beef cows in which the producer needs to increase levels quickly or there are antagonists in the forage and/or water. Changes in liver Cu and Zn concentrations were not accompanied by changes in serum Cu and Zn levels, which implied that serum levels did not reflect changing trace mineral status. Providing trace mineral supplements with antagonistic minerals to first-calf beef heifers only 30 d prior to parturition did not influence calf Cu and Zn liver levels. Increased serum Cu levels observed at 4 d of age indicated that Cu is removed from the liver and is transported by the blood, suggesting that liver Cu levels are important for adequate Cu balance in the young calf.

Results of the swelling test suggested that high levels of Mo, S and Fe may inhibit cell-mediated immune response when beef cattle are supplemented with Cu and Zn (41). However, heifers supplemented with either CX or IN did respond more rapidly than the control group. Both Cu sources were retained at the same level, but zinc methionine appeared to be more bioavailable as indicated by increased retention compared to zinc sulfate.

The change in cycling activity observed among treatments from 45 d post-calving to the breeding season suggest that complexed minerals may be affecting another metabolic process in the heifer that delays expression of estrus early in the postpartum period (41). This effect appears to diminish by the beginning of the breeding season because more cows receiving complexed minerals were bred AI.

Supplementation of the Replacement Heifer

Recent research has shown that supplementing Cu, but not Zn, resulted in a decrease in efficiency of gain. Because the antagonist Mo, has been shown to depress liver concentrations of Cu, it has been suspected that when supplemental Cu was fed, it combined with the antagonists to form insoluble complexes and further exaggerated a deficiency. Recent studies indicate that an interaction between supplemental Cu and Zn does take place. Galyean et al. (1995) suggested that increasing Cu (20 ppm) intake without a corresponding increase in Zn resulted in a decrease in efficiency of gain by weaned calves. Other data (30) suggested that Zn supplementation improved efficiency of gain. However, excessive dietary Zn can negatively effect Cu status through the absorption process (31).

The objective of this experiment was to further understand the implications of supplementing Cu and Zn either independently or in combination for weaned heifer calves. These diets were fed with a high level of Mo in the diet (6 ppm).

Materials and Methods

Thirty individually fed heifer calves (avg. wt. 550 lbs.) were allotted to a 2 x 2 factorial arrangement of treatments comparing different levels of supplemental Cu and Zn. These elements were provided from an organic-complexed form. A basal ration (10% crude protein) of chopped grass hay (76%) and a corn-based concentrate (24%) were fed to allow a 1.5 lb/day gain (Table 3). A fifth treatment was evaluated in which sulfate forms of Cu and Zn were compared to the complexed treatment. Also, 6 ppm of Mo was fed to deplete liver Cu and/or interfere with Cu and Zn absorption.

The five mineral treatments were: 1) No Added Cu or Zn; 2) Added Cu (complexed form), no added Zn; 3) No added Cu, added Zn (complexed form); 4) Added Cu and Zn (complexed form), and 5) Added Cu and Zn (sulfate form). Expected intakes of dry matter, Cu, Zn and Mo are presented in Table 4. All calves were fed for 90 days. Liver biopsies were conducted at day 1, 15, 58 and 90 of the experiment and tissue was analyzed for Cu and Zn.

Results

Rate and efficiency of heifer gain are presented in Table 5. Feed intakes tended (P<0.15) to be higher for heifers fed diets without supplemental complexed-Cu (avg. 15.1 lbs./day) compared to heifers with supplemental Cu (avg.14.7 lbs./day). Diets supplemented with complexed-Cu likewise tended to have faster (P<0.19) daily gains than diets without complexed-Cu (avg. 0.97 vs 0.83 lb./day; respectively). Similarly, gains tended to also be faster for diets supplemented with Zn vs no Zn. There were no significant differences in rate and efficiency of gain when the inorganic (Cu and Zn sulfate) was compared to the complexed Cu and Zn treatment.

Feed conversions were numerically improved (P<0.16) for diets supplemented with Zn (avg. 15.3) compared to diets without supplemental Zn (avg. 18.5). Results would appear to be similar to those reported by North Carolina State workers who found that supplemental zinc methionine tended (4-7%; P=0.14) to improve daily gains in grazing steers over two years.

Table 6 presents the changes in liver Cu and Zn for the 90-day study during which heifers were fed 6 ppm Mo in the total diet. Because heifers were allotted to treatments based on initial body weights, initial Cu and Zn concentrations were different among treatments. More importantly however, were changes in liver Cu and Zn at the end of the 90 day experiment. Heifers fed both complexed Cu and Zn had the greatest increase in liver Cu (203%) followed by heifers fed Cu alone (124%) followed by control heifers (108%). When additional zinc was added to the diet without Cu, liver Cu levels declined to 59% of the original value. This suggests that both Zn and Cu must be increased in the diet to prevent a decline in Cu liver stores. There was no difference for Cu uptake, as a percentage of initial liver concentrations when comparing the complexed Cu and Zn treatment to the copper and zinc sulfate treatment.

Changes in liver Zn are in disagreement with previous studies conducted by our group (2). In this study, Zn levels were actually higher for non-supplemented heifers compared with supplemented.

Summary of MSU Studies Suggest:

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