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Think Zinc

By: Gilda V. Bryant

Are you seeing some lame or poor-doing critters out there? It might be a good idea to give zinc some consideration.

Zinc works hand-in-hand with copper and selenium, but when it comes to supplementation this trace mineral is a work horse. It’s involved in some 300 enzyme systems including the metabolism of proteins and carbohydrates, which provide energy for growth and weight gain in cattle. Required for every phase of cell growth, zinc is necessary for tissue health and is essential for the proper function of reproductive and immune systems. Unfortunately, zinc is hard to come by in most American forages. Producers may not be aware of a zinc deficiency until animals develop problems such as footrot.

“It’s not uncommon to see cattle that are limping because of the problems they are having with hoof integrity,” says Steve Blezinger, PhD, PAS (Professional Animal Scientist), a ruminant nutrition and management consultant. “A lot of cases can be traced back to zinc deficiency that can lead to a breakdown of connective tissue that is so important in the makeup of the hoof. You have a situation where that hoof is a little more susceptible to infection when stepping on rough ground or sharp objects.”

Butch Whitman, PhD, PAS, Vice- President of Nutrition Programs at Westfeeds, says, “Moderate deficiency symptoms are fairly hard to observe, but are probably the more predominant one that producers experience. Moderate deficiencies retard growth rate, impair reproductive performance and the animal’s immune system, which is going to show itself as chronic health problems.” Whitman adds, “In extreme cases, you get severe restriction of growth and reproductive performance and have very poor health because of poor immune systems.”

For example, calves with low zinc levels aren’t able to mount a positive response to vaccines. And that means sick calves with reduced growth and weight gain. Stressful events, including calving, weaning, moving to a new location or environmental changes such as drought, tend to lower zinc levels in the animal. Eric Scholljegerdes, PhD, Assistant Professor in the Animal and Range Sciences Department at New Mexico State University, warns that cattlemen who work animals in a high stress manner potentially cancel all the good management practices done up to that point. He continues, “The animal is going to be exposed to pathogens no matter what, so if you do as much as you can to keep the stress level down so the body has the ability to mount a response, the better off the animal is going to be.”

Zinc is vital for bulls and a healthy calf crop. Although many producers tend to forget about their bulls until turnout, low levels of zinc can cause a reduction of spermatogenesis (sperm creation), testicular development and sperm volume. Zinc is also involved in the process that creates healthy, mobile sperm cells. Since the sperm that are produced today began developing some 90 days earlier, ranchers need to supplement with zinc well in advance of breeding season. How can cattlemen evaluate zinc availability to their herds?

“Start with an evaluation of the forages the cattle are grazing,” Whitman explains. “If you do that over time, you’re aware of unique problems in the area in which you’re raising cattle. You have to do that at different times of the year including harvested forages that are fed through the winter as well as grazed forages as cattle move to different pastures.”

Consider testing the water supply, which will not only give an indication of zinc levels, but also the level of other minerals that either enhance or prevent zinc absorption. If a producer doesn’t have a clear idea of zinc availability after forage and water testing, taking blood samples might be the next step, although these tests tend to provide an incomplete picture.

“Zinc is very transient in the body,” Blezinger explains. “You can get a reading of X milligrams of zinc per deciliter today, which might indicate an inadequate status when in actuality that cow may be deficient. She has just mobilized so much zinc that it’s in the blood stream, not in the liver. If she is under stress, it will mobilize more zinc and copper out of storage areas into the blood stream.” Most experts agree that free choice loose minerals work best for supplementation. Ranchers have more formulations to choose from and loose minerals provide more flexibility when feeding. Trace mineral injections may also be used with free choice minerals.

If the herd needs higher levels of zinc for optimal performance and health, consider adding chelated zinc to the mineral program. Also know as a complexed or organic mineral, micro minerals such as zinc are chemically bound to a protein or amino acid, making them more available for absorption in the small intestine. Chelated zinc may also need to be fed to overcome the effect of antagonists. Antagonists are natural compounds which can bind with zinc to make it unavailable to the animal. Occasionally, calcium and phytate, a form of phosphorus usually found in plants, bind zinc.

However, it’s much more likely that zinc will affect copper absorption. “At one time copper was The Thing,” Blezinger says. “For a while that was the only mineral anyone focused on. Over the last couple of years, I’ve seen more focus on zinc. We’re seeing some high zinc levels in some of these mineral supplements. In my opinion, we’ve gone overboard in some cases. We may be creating an antagonist situation between zinc and copper.”

He advises cattlemen to read the label, especially zinc to copper proportions.Look for a four to one (4:1) ratio, with zinc being four and copper, one. Blezinger has seen ratios as high as ten to one, which can reduce the absorption of copper.

Scholljegerdes adds, “If you have problems with zinc, there are going to be problems with other trace minerals as well. Feed a well-balanced mineral supplement especially if animals are facing times of high stress. These good mineral packages can be expensive. If you want to save as much money as you can, pick the times when you know your animals are going to have issues with stress and nutrient deficiencies during fall and winter. Splurge and take care of those girls a little better, then you can go to something a little less expensive when grass quality improves. You’ve got to have mineral year round.” Whitman offers this advice. “When producers are providing a mineral supplement package, make sure it’s balanced. Don’t get carried away with [one particular] nutrient.”

Zinc is essential for animal health, reproduction and the proper functioning of cellular processes throughout the body, including building DNA and proteins. Without a complete mineral package, cattle won’t perform at their genetic potential. Why not think zinc?

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