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HIGH LEVELS OF SULFUR IN A COW'S DIET CAN AFFECT COPPER ABSORPTION

by: Stephen B. Blezinger
Ph.D, PAS

One of the nutritional buzz words in the beef cattle industry is copper. The need for copper in the diet has been well documented by numerous researchers in many states. Cattle producers have, over recent years, become well aware that high levels of sulfur molybdenum and other minerals in a cow's diet can affect her ability to absorb copper. Through the use of sulfate-based fertilizers and output from lignite coal burning power-plants, the levels of S in forages has trended higher over the years thus increasing the problem of the presence of antagonists that can reduce copper absorption in the animal.

The Need for Copper in the Animal

From the producers perspective the most common effect he sees in situations of copper deficiency is hair pigment loss or discoloration. The reddening over the shoulders and down the top line of dark colored cattle is well recognized. More extensive deficiencies result in this pigment loss around the edges of the ears and around the muzzle. While this is fairly easy to spot in black cattle, lighter-colored cattle (a. e. Charolais) pose more of a challenge. Light colored cattle adopt more of a dull coloration of the hide and lose a lot normal hair coat luster. Color, however, is only the tip of the iceberg.

Copper is required for the activity of enzymes associated with iron metabolism, elastin and collagen formation, melanin production, and the integrity of the central nervous system. It is required for normal red blood cell formation by allowing iron absorption from the small intestine and release of iron in the tissue into the blood plasma. Ceruloplasmin is the copper-containing transport protein. Copper is required for bone formation by promoting structural integrity of bone collagen and for normal elastin formation in the cardiovascular system. Copper is required for normal myelination of brain cells and spinal cord as a component of the enzyme cytochrome oxidase which is essential for myelin formation. Maximum immune response is also dependent on copper as indicated by depressed titers in deficient animals.

As discussed, the process of normal hair and wool pigmentation requires copper. It is believed that copper is a component of polyphenyl oxidase which catalyzes the conversion of tyrosine to melanin and for the incorporation of disulfide groups into keratin in wool and hair.

Effects of Copper Deficiency in the Animal

Copper deficiency symptoms include depraved appetite, stunted growth, suppressed immune system, rough hair coat, anemia, diarrhea, straight pasterns, depigmentation of the hair, and sudden death (falling disease). Reduced growth in cattle seems to be most dramatic when excess molybdenum causes the copper deficiency. In these cases liver and plasma copper concentrations may not reflect a copper deficiency. This has caused some to hypothesize that the excess molybdenum causes a “localized copper deficiency” within the body. In one study copper supplementation decreased antibody titers in unstressed calves, but increased the titers in stressed calves. Although copper is critical to a healthy immune system, there are other physiological barriers that can override copper status.

Copper nutrition has been shown to have great impact on fertility in cattle. Sub-optimal ovarian activity, delayed or depressed estrus, reduced conception rate and calving difficulty have been associated with copper deficiencies in beef and dairy cattle.

Also, several studies at North Carolina State University have shown the role of copper supplementation on carcass composition. Copper supplementation (10 mg/kg diet) has altered fat metabolism and tended to increase plasma norepinephrine concentrations in feedlot cattle. This resulted in a reduction in back fat which will improve the red meat yield per carcass and result in less waste. Also, the increased polyunsaturated fatty acid concentration in muscle of copper-supplemented steers may result in a healthier product for human consumption.



Copper/Sulfur/Molybdenum Interactions – Some Biochemistry

A minimum requirement for copper cannot be given with great accuracy, since copper absorption and utilization in the animal can be markedly affected by several mineral elements and other dietary factors. Zinc, iron, molybdenum, inorganic sulfate and other nutrients can reduce copper absorption. These interactions and their effects are not well understood.

Requirements for copper can vary from 4 to 15 mg/kg (parts per million, ppm ) of daily dietary intake depending largely on the concentration of dietary molybdenum and sulfur. The recommended concentration of copper in beef cattle diets is 10 mg Cu/kg diet as noted in Table 1. This is based on recommendations by the National Research Council for Beef Cattle (1996) and is believed to provide adequate copper if the diet does not exceed 0.25 percent sulfur and 2 mg Mo/kg diet. Less than 10 mg Cu/kg diet may meet requirements for feedlot cattle since copper is more available in high concentrate diets than in forage diets. Copper requirements may be affected by breed. Breeds such as Simmental and other Continental European Breeds tend to exhibit either a higher requirement for Cu or a lower inherent ability to absorb this trace element. One study has reported that Simmental and Charolais cattle had a greater copper requirement than Angus. In this case, differences in biliary (secretions from bile) secretion may explain the differences among breeds. Regardless of dietary treatment, biliary copper excretion was twice as high in Simmental compared to Angus cattle. More research is needed in this area.

As noted above, copper availability is greatly affected by the presence of both molybdenum and sulfur. The antagonistic action of molybdenum on copper metabolism is greater when the ration is also high in sulfur. Copper is believed to react with thiomolybdates (sulfur and molybdenum complexes) in the rumen to form poorly absorbed insoluble complexes. However, some thiomolybdates are absorbed and affect copper metabolism in the body. It has been discovered that thiomolybdates cause copper to be bound to blood albumins which renders the copper unavailable for any biochemical reaction in the body. They also may directly inhibit certain copper-dependent enzymes.

Sulfur reduces copper absorption, possibly through the formation of copper sulfide in the rumen which is poorly absorbed later in the intestinal tract. High concentrations of iron and zinc also reduce copper status, which may increase copper requirements. These elements appear to compete with copper directly for absorption sites on the intestinal wall.

Likewise, copper availability changes with the forage specie and method of preservation or storage. Curing or drying of forages may alter the chemical form of copper, making it more available than copper in fresh green plants. Fresh grass has the lowest availability of copper. This availability is further reduced by small increments of molybdenum and sulfur in the forage. In forages preserved as hay, the antagonistic effects of molybdenum are detectable, but less than that of sulfur. In silages, molybdenum has a small effect but sulfur reduces copper availability in a logarithmic manner. These variations in copper availability with preservation and storage method are probably due to changes in the release rates in the rumen of copper and its antagonists.

Evaluating the Sources of Minerals

When evaluating mineral interactions and their effect on copper, it is essential to consider all the dietary nutrient sources including forages, feed, mineral supplements and water. For example, a recent study showed that reducing the sulfate content of drinking water from 500 to 42 mg per liter increased copper availability. This effect is independent of molybdenum, and probably results from the formation of insoluble copper sulfide as noted previously.

The milk of certain species such as cattle, sheep, goats, pigs, dogs and rats is quite low in copper. In dairy cows, the level of copper is generally below 0.1 ppm, although it may go as high as 0.2 ppm after calving. But, if the dam's intake of copper is adequate, the newborn will have a substantial storage of copper in the liver. The liver is the main storage organ for copper. With most species, liver copper levels are higher in newborns than in adults. Copper in the milk cannot be increased beyond the normal range by adding extra copper to diets already adequate in copper.

When considering the copper-sulfur relationship the producer has to understand several issues:

1) Copper and sulfur from natural sources (forages and water) is variable. The only way to know for sure what the level in a given area may be is to have samples analyzed.

2) The copper-sulfur relationship is based on the total amount of each element in the diet from all sources, forages, feeds, mineral supplements and water.

3) Selection of mineral supplement is ideally based on knowledge of copper and sulfur levels from forages as well as other dietary sources.

In situations when we know sulfur is high (>.25 to .35 percent depending on your source of information) the amount of copper provided per head per day will need to be increased. There are no hard, fast rules for how much it should be increased in these situations but generally increasing Cu levels about 50 percent should be adequate although some nutritionists will recommend even higher levels than this. Per the information in Table 1 we know that the maximum tolerable level for beef cattle is 100 mg/kg (ppm) but we would not want to come anywhere near this due to the possibility of creating other imbalances.

Let's look at an example on how to consider copper and sulfur levels in a cow herd's diet. For simplicities sake we'll assume we have tested the water and only trace amounts of sulfur were found:

With this diet composition we see that the overall sulfur level does not appear to exceed the threshold for concern. We also see that the copper would appear to more than compensate for dietary needs. A couple of things that need to be considered:

1) As noted previously, sulfur levels in forages are highly variable. While a test may come back at .20 percent remember that you only tested a very small portion of what the cow will eat over the haying months, she could easily get into a batch of hay that will exceed the sulfur levels we are concerned with.

2) The sulfur level in the mineral appears quite high (1.15 percent). This is not uncommon in minerals that use sulfate sources of the minerals that it contributes (manganese, copper, zinc, etc. See Table 2). In the big scheme of things, however, the amount of actual sulfur that the mineral contributes is very small, only .01 percentage point to the total. While the use of sulfated trace minerals is not imperative they are much more bioavailable than oxide sources and thus actually improve the overall absorption of the element in question.

3) While the overall copper concentration in the diet shown appears high remember that the copper is not 100 percent available. The forage source may be 50 percent or less, the mineral, depending on the product may range from 35 to 75 percent available and the cubes may only be 50 percent available. This means that the Cu level in this diet may only be about 12.75 ppm. This could still be on the low side.

In this situation the producer may very well decide to take steps to increase the amount of copper provided to the animal. The two easiest steps would be to a) increase the amount of copper in the mineral supplement. He might choose a product that would run 2500+ ppm in copper, and/or b) consider using a product that includes an organic or chelated form of copper. Organics, while more expensive have been shown to be significantly higher in bioavailability compared to sulfates, oxides or carbonated forms of trace minerals. Normally a mineral product of which 30-35 percent of the copper is from an organic source is preferable.

Conclusions

High sulfur or molybdenum levels in forages are not the end of the world when it comes to providing copper. The keys handling this situation are knowing what you have (forage testing), doing the math to know where the animal's total dietary intakes are (from ALL sources) and selecting a product that will do the best, most cost effective job in providing for the animal's needs.

Dr. Steve Blezinger is a nutritional and management consultant with in Sulphur Springs, TX. He can be reached by phone at (903) 885-7992, by mail at 667 CR 4711 Sulphur Springs, TX 75482 or by e-mail at sblez@peoplescom.net.

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