Today's genetics allow cattle to perform dramatically better than their 1960 counterparts, both on grass and in the feedlot. To realize that potential, however, cattle must have the correct nutritional "fuel," says Dennis Herd, Texas A&M beef cattle nutritionist.
Luckily, much more is known today about nutritional requirements and dietary interactions. This is particularly true in the case of trace minerals, required nutrients that can lead to major efficiency breakdowns, he says.
"Balance" is the first place to start in designing a mineral/nutrition program, Herd says. "It won't make you money to furnish cattle 150% of their mineral needs if they're only receiving 85% of their protein and energy needs or vice versa," he says.
There are at least 17 minerals (in two classes - macrominerals and microminerals) that the National Research Council says are required by beef cattle. Macrominerals include calcium, magnesium, phosphorus, potassium, sodium, chlorine and sulfur. These are nutrients required in large amounts (grams) per day, hence the name "macro" nutrients.
The microminerals are also called "trace" minerals because just milligrams are required per day. They include chromium, cobalt, copper, iodine, iron, manganese, molybdenum, nickel, selenium and zinc.
Trace mineral requirements c an be met through feedstuffs, but often they're not - particularly in a grazing situation, says Wayne Greene, Texas A&M beef cattle nutritionist in Amarillo. A low mineral content in the forage, heightened by the presence of antagonists, is often the problem, he adds.
"Cattle may appear to be doing fine while sub-clinical deficiencies of vital trace minerals can be robbing them of feed intake and efficiency, growth, reproductive efficiency and the ability to fight sickness," Greene says.
Herd adds that trace mineral supplementation needs are greater today than ever before for a number of reasons. For one, the increased productivity or genetic potential of cattle may have increased requirements.
Genetics may also affect cattle's susceptibility to deficiency and toxicity. Research shows that Simmental and Charolais cattle need more copper in their diet than Angus. Within breed genetic effects or differences likely exist as well.
"Field experience suggests Simmental, Maine Anjou, Limousin and Charolais benefit from 1.5 times the copper intake of traditional breeds," Herd says.
Modern farming methods are another factor. Feedstuffs derived from crops fertilized with nitrogen, phosphorus and potash tend to decline in trace mineral content over time - particularly shallow-rooted crops.
"Many health problems and failures of commonly accepted disease treatments have had trace mineral deficiencies as the root or contributing factor," Herd says. That's not surprising, since research on copper, zinc and selenium shows them to be essential to a good immune system.
A Balanced Diet Confinement operations function at a big advantage over grazing operations, Herd says. The diet of a range cow can't be balanced as easily or as accurately as a confined animal. "But it's the only way to address some mineral problems where excesses of certain minerals are present along with low or deficient levels of another," he adds.
A balanced diet means balanced rations. To do that, the following information is needed:
* Nutrient requirements of the particular class of cattle.
* Nutrient content of the feeds. Since book values often overestimate the level of trace minerals in many common feedstuffs, forage testing for minerals in grazing and hay crops is often needed.
* Mineral content of the water, particularly if high in iron or sulfur.
* Estimate of feed intake. A rough guide would be 1.5% of body weight for very coarse poor forage, 2% for average and 2.5% for good forage.
Next, identify the mineral requirements of the animal (Table 1). Requirements can vary by health situation, performance expectations, even by breed, Herd says. As a result, many nutritionists "formulate" to levels above those considered minimal. The amount of additional "insurance" will vary with the mineral, its cost and the potential detrimental effects an excess may cause.
Many minerals interfere with the utilization of other minerals at levels well below the maximum tolerable level, Herd says. For example, it's usually beneficial to increase the copper level above the listed requirement any time molybdenum exceeds 2 ppm, sulfur exceeds 0.3%, iron exceeds 250-300 ppm or some combination exists. All minerals can be involved in interactions, but the effect other minerals have on the need for copper appears more specific and unique than with many of the other minerals.
In determining the level of total dietary mineral desired and thus supplement intake and formulation, keep in mind the following points, Herd points out:
* Higher levels of mineral intake may be needed and safe to play catch-up in a problem herd than to sustain it once the problem situation is corrected.
* The requirement variations that occur with the cow's stage of production isn't defined for trace minerals as it is with major minerals, protein and energy. Contrary to the general higher requirements for protein, energy, calcium, etc., during lactation, the requirement for copper and selenium may be equally high or evenhigher in late pregnancy than during lactation.
Forage Testing Forage testing is the foundation for establishing the need for and the amount of supplemental minerals. Soil testing helps explain the composition of the forage, but it isn't reliable in directly evaluating the mineral status of the animal. Blood testing and liver analyses on any dead cattle, however, can add additional information concerning a herd's mineral status.
But, it's the knowledge of estimated dietary mineral intake from both feed and water that provides the basis for correcting deficiencies or adjusting for mineral excesses. Even crude estimates are helpful as opposed to total guesses.
Once a good feel for the mineral content of the diet is reached, compare the levels to those desired and develop a supplement to make up any deficiencies, Herd says. Where the mineral content of the diet is unknown, he formulates the trace mineral supplement to provide 100% of the NRC requirement.
"Once you're comfortable that you know dietary mineral intake, adjust individual mineral levels to meet your goals," Herd says. "The bioavailability of trace minerals in forage is often not very high. Use only mineral forms and sources known to be reasonably high in digestibility, absorbability and bioavailability."
Here are some points Herd suggests to keep in mind while supplementing:
* Manage the mineral nutrition of cattle just as you'd manage protein and energy. Don't trust cattle to regulate how much mineral they'll consume.
* If supplementing protein and/or energy, include a minimal level of minerals in the protein and energy supplement to help ensure intake.
Copper All trace minerals are important, but copper, selenium and zinc are of the most serious and widespread concern.
Copper deficiency is usually found in grazing animals because the copper in grass has less bioavailability to cattle than copper in hay and grain, says Texas A&M veterinarian Steve Wikse. Animals most affected are herd individuals with the highest requirements - calves and yearlings.
The symptoms of copper deficiency are varied. Not all are seen in a herd, he says. Clinical disease generally involves young grazing animals, the classic picture being a calf with a rough hair coat diluted in color.
Other clinical signs may be diarrhea, anemia, lameness, even osteoporosis. Studies have shown differences in weaning weight between treatment and control groups usually ranging from 20-50 lbs., Wikse says.
Copper deficiency is a problem throughout the U.S., Wikse says. A 1992 NAHMS (National Animal Health Monitoring System) reported on a survey of trace mineral concentrations in forage on 327 ranches in the 18 largest beef producing states. NAHMS found that 64% of the forage samples were marginal or deficient in copper.
Actually, says Wikse, the overall availability of copper to the cattle grazing these forages was probably lower yet due to the marginal to high antagonistic levels of molybdenum and iron present in the samples.
Copper deficiency occurs as a primary deficiency when the concentrations of copper in the diet are low. A conditioned deficiency occurs when absorption and utilization of copper is hindered by other minerals in the diet -usually, molybdenum, sulfur and iron; less commonly, zinc and cadmium.
For grazing cattle, prevention methods include copper glycinate injection (no longer commercially available), incorporating copper in a free-choice salt/mineral mix, or copper boluses (copper oxide needles).
"Our recommendation is to try to remedy a copper deficiency with a trace mineral supplement that contains relatively high concentrations of copper," Wikse says. "After 6 to 8 weeks, bleed some individuals and measure copper concentrations in their serum."
If at-risk cattle aren't consuming enough copper through the free-choice supplement, Wikse and Herd suggest going the copper bolus route.
Copper oxide boluses are filled with short segments (4 mm) of processed copper oxide wire that lodge in the rumen and reticulum. Small copper oxide particles slowly wash to the abomasumwhere acidity dissolves them and releases the copper for absorption in the intestines. Bolused properly in the spring, a single dose provides sufficient dietary copper for a 6- to 8-month period, Wikse says.
"Bolusing is a more labor-intensive alternative," Wikse says, "but the copper boluses have been shown to be effective when consumption of free-choice mineral is a problem."
Zinc Zinc is the trace element most commonly deficient in grazing animals. The 1992 NAHMS study found that of 352 forage samples from 327 cow/calf operations in 18 states, only 2.5% tested in the adequate range for zinc.
Zinc is essential to an effective animal immune system, Wikse says. Zinc deficiency can result in reduced growth, feed intake and feed efficiency; listlessness; reduced testicular growth, swollen feet; failure of wounds to heal and hair loss.
Besides the degree of deficiency, the life stage at which the deficiency happens largely determines the degree of the negative effect.
The only delivery method for zinc is in a mineral mix. Feed-grade sources of bioavailable zinc include zinc oxide, zinc sulfate, zinc methionine and zinc proteinate. A controversy has long raged over the use of organic forms of zinc versus chelated. Wikse says, as a rule, organics are less expensive but chelates tend to be more efficient because they are better absorbed.
Selenium Selenium is critical to the immune system. In young animals a deficiency can produce weak calves that can die early in life, or unthriftiness with weight loss and diarrhea in older calves and adults. It can also contribute to such calving problems as lowered fertility, retained placentae and abortions.
The function of selenium and vitamin E are interrelated. A diet low in vitamin E may increase the amount of selenium needed to prevent certain abnormalities such as white muscle disease.
The traditional selenium-deficient areas are the Northwest, Northeast and Southeast. Selenium can be administered to cattle by supplementation in the diet or injection every three to four months during critical production stages.
"Absolutely, the most critical time to make sure you have a trace mineral supplement before cattle is the six-month period that includes the last two months of pregnancy and the four months after," Wikse says. "Your supplement should have high levels of the minerals deficient in your area. The payoff will be increased calf health and better pregnancy rates."