VITAMINS ARE IMPORTANT IN BEEF CATTLE DIET

by: Stephen B. Blezinger
Ph.D., PAS

Part 1

As most cattle producers know every nutrient has importance and value in the animal. All cells, tissues and organs require all the nutrients at some level to develop, grow and function. An important nutrient group in all mammals are the vitamins, small molecules required at low but essential levels in the animal. In beef cattle we typically focus on Vitamins A, D and E. These are referred to as “fat-soluble” vitamins and we commonly see them stored in fat depots. Unfortunately, the way the beef cattle nutrition industry has developed over the years, the common focus is on Vitamin A. Vitamin A is typically listed on feed and supplement tags as required by regulators in most states. It's also required by the animal in the highest volumes so certainly it is important. Vitamin D or D-3 as it is often called, is given less importance in many producers minds because we have been told that it is produced in the skin as a reaction to exposure to sunlight. For cattle that spend most of their lives outside in the sun, we generally assume that they can manufacture all they need. This may not be entirely true. Finally, Vitamin E, while gaining a lot of press over recent years is still not all that well understood by the producer but nonetheless is critically important especially in terms of reproductive and health performance.

This article is the first in a series that will discuss the vitamins. We will begin an examination of all the vitamins, not just A, D and E but the water soluble or B-Vitamins as well. B-Vitamins have also been shown to be of significant importance in cattle diets as well although as with Vitamin D, we have believed that in grazing cattle, B-Vitamins don't need to be fed/supplemented because they are produced in quantity by the rumen microbes. This is true but in some situations the amounts produced by these bacteria may not be adequate. So this issue will be discussed as well.

So to start us off we'll take a look at the fat-soluble vitamins, the ones we hear the most about but we'll start from the back, with Vitamin E, and delve into its back ground and importance.

Starting with Some History

Vitamin E (E) is involved with the control of nerves, muscles and the senses. Contraction of muscles allowing movement, heartbeat, rumen and lung function, are all influenced by vitamin E. Excretion of manure, growth, feed conversion efficiency, and reproduction are also affected. It has been noted that the incidence of mastitis and retained placentas increase when E is deficient in pre-calving cow diets. Reproductive performance of cows and bulls is reduced if E is deficient.

Vitamin E was first identified as nutritionally essential for animals about 60 years ago. In lab studies rats fed purified diets without E did not reproduce. Similar studies over the years have shown likewise results in domestic, managed species (cows, pigs, horses, poultry, etc.). From that time, much has been learned about the biochemistry of E, and the requirements have been established for laboratory animals. Progress in accurately defining the E requirements of cattle, however, has been slow. In other words, defining the exact requirements in beef cattle for E has been challenging. The standard method of defining a nutrient requirement is to feed different amounts of the nutrient and measure a certain response influenced by the nutrient. This might include weight gain, cycling activity, responsiveness of the immune system, etc. The requirement is the point at which an increase in the intake of the nutrient no longer increases the response measured. Use of this method is dependent on the ability to measure accurately and precisely both the intake of the nutrient and the response. For many nutrients and many species of animals, this method works well, but attempting to define the E requirement of beef cows presents several challenges. Vitamin E intakes are very low (usually less than a few grams per day), and concentrations of E in normal feedstuffs is variable. Therefore, accurately measuring E intake by cattle is difficult. Vitamin E can be stored in certain organs (mainly liver), and these stores can mask a short-term dietary vitamin E deficiency. Several weeks or months may be required to deplete cows of vitamin E. So all this said, because of these and other problems, the true requirements for vitamin E in cattle has not been well defined. The E requirement given by National Research Council (NRC) is largely based on prevention of white muscle disease, a disease that presents itself when E supplies are very low or deficient, especially in very young, growing animals. Nonetheless, we know a requirement exists for breeding and growing cattle and nutritionists and producers alike do the best they can in estimating and meeting this need.

Requirements vs. Recommendations

Let's talk for a second about nutrient requirements and recommendations. A requirement is the amount of a nutrient needed to maintain the health of an animal, allow for successful reproduction and allow for a certain amount of production (for example, milk) under specific conditions. A recommendation is the amount of a nutrient that will meet the requirement under less defined conditions and will include a margin of safety to account for variations in intake, nutrient composition of the diet and production by the animal. The E content of feedstuffs fed to cattle is extremely variable (Table 1), but the cost of analyzing feeds for vitamin E prevents its routine measurement in feeds. Therefore, the actual E content of many diets will not be known, and the amount of E fed should include a safety margin. A recommendation must also consider the cost of the nutrient, the cost of a nutrient deficiency and the potential for toxicity. For E, toxicity is not a major concern. The NRC suggests that ruminants can tolerate intakes of about 40,000 IU/day of supplemental E for several months without adverse effects (this is 25 to 80 times what is normally supplemented to cattle).

Let's Chase a Rabbit

As with all the fat soluble vitamins, E is measured and reported in terms of “international units” (IU) and the recommendations are reported in IUs per day. An IU is a unit of measurement for the amount of a substance, in this case a vitamin, based on biological activity or effect. In the vitamins it is related to the biological equivalent of the active ingredient in a given vitamin. For instance:

• Vitamin A: 1 IU is the biological equivalent of 0.3 microgram (μg) of retinol, or of 0.6 μg beta-carotene.

• Vitamin D: 1 IU is the biological equivalent of 0.025 μg cholecalciferol.

• Vitamin E: 1 IU is the biological equivalent of about 0.667 mg d-α-tocopherol (2/3 mg exactly), or of 0.45 mg of dl-α-tocopherol acetate.

So based on this, if we are feeding 100 IU's of E daily to a beef cow the active ingredient we might use would be either 66.7 mg of d-α-tocopherol or 45 mg of dl-α-tocopherol acetate.

And while we are on the subject, note that Vitamin A and D active ingredients are expressed in micrograms (μg) while E is expressed in milligrams. A milligram (mg) is 1000 μg.

So this said, as you can see, the units used to express the vitamins are actually related to specific units of measure or amounts of a given compound toe fed per day.

Vitamin E Content of Feeds

The average concentrations of E for several feeds are shown in Table 1. As discussed previously, values for E concentrations really do not have a lot of value because of the large variability in concentrations. For example, the coefficient of variation (CV) for vitamin E content of corn grain is 50 percent. The indigenous E content of grins and proteins is related to the concentration of fat in the product. Feeds with higher concentrations of fat tend to have higher concentrations of vitamin E. Feed processing and length of storage have a large impact of E concentration. For example, raw soybeans contain substantial amounts of E; however, roasted soybeans have low concentrations. The heat processing destroys much if not all of the vitamin. Fresh, green forage is an excellent source of E, and E concentrations in high quality pasture may exceed 100 IU/1b. of dry matter. Vitamin E concentrations decrease rapidly and dramatically after a forage plant has been cut. The longer the cut forage is exposed to sunlight and oxygen, the lower the E concentration. Forages are typically wilted or dried one or two days before ensiling or baled as hay. From that point silage is maintained in an anaerobic (no oxygen) environment. Silage usually contains more vitamin E than hay (wilted for a longer period and exposed to oxygen during storage) but significantly less E than fresh forage. Also, as with most nutrients, concentrations of E decrease as forage plants mature.

Assessment of Vitamin E Status of Cows

As noted above, E is supplied by the feeding different forms of α-tocopherol (chemical, active form of E). Plasma concentrations of α-tocopherol in cows are correlated with intake of E, but factors other than E intake can influence plasma α-tocopherol concentrations. Plasma concentrations of α-tocopherol are significantly lower during the peripartum period than during lactation and gestation. The concentration of α-tocopherol in plasma is highly correlated with plasma concentrations of cholesterol with cholesterol concentrations indicative of blood lipid (fat) concentrations. Feeding fat in one or more of several forms to cows will increase plasma α-tocopherol concentrations in dry cows but not in lactating cows. This means that increasing fat intake in cows prior to calving will have a positive influence on the E status in those cows. Another interesting finding is that stress induced from excessive handling, epinephrine or an ACTH injection reduced the concentration of α-tocopherol in plasma of beef cattle. This indicates that newly received or incoming cattle will more than likely have a substandard E status and will need to be supplemented accordingly.

Effects on Immunity and Reproduction

In a study of 50 different herds (544 samples), mean serum concentration of α-tocopherol was 2.4 mg/liter. Based on neutrophil function, a cell type primarily involved in immune response, the suggested minimal plasma concentration of α-tocopherol was 3 to 3.5 mg/liter. Low plasma concentrations of α-tocopherol were found to be a significant risk factor for clinical mastitis and other types of infection (respiratory, digestive system, etc). Dairy cows with plasma concentrations of α-tocopherol less than 3 mg/liter were 9.4 times more likely to have clinical mastitis than cows with concentrations greater than 3 mg/liter. This shows the importance of maintaining an appropriate vitamin E status in the animal in support of a properly functioning immune system. A study with beef heifers in 1991 found a high correlation between serum concentrations of α-tocopherol and pregnancy rate. Once serum concentrations were greater than 3 mg/liter, no additional improvement in pregnancy rate was observed.

Recommendations

So based on all this and the fact that the actual requirements are not well defined we still need to establish some type of recommendation for feeding levels. Some recommended levels are:

Pregnant cows: 200 to 300 IU per day

Lactating Cows: 300 to 500 IU per day

Young Calves: 80 to 150 IU per day: Growing Calves: 100 to 200 IU per day

Finishing Steers/Heifers: 400 to 1250 IU per day

Conclusions

Obviously, E plays an important, if not well-defined role in the overall nutrition cattle. Much of this will depend on age, stage of production, stress levels and so on. It is important for the producer to understand what he needs to be shooting for in his given situation. A nutritionist or veterinarian should be able to help you define these numbers and provide guidance on how to best meet these requirements. In Part 2 of this series we will discuss Vitamin D and its requirements and recommendations for beef cattle.

Dr. Steve Blezinger is and nutritional and management consultant with an office in Sulphur Springs Texas. He can be reached at 667 CR 4711 Sulphur Springs, TX 75482, by phone at (903) 885-7992 or by e-mail at sblez@verizon.net. For more information please visit us on Facebook at Reveille Livestock Concepts.







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