VITAMIN E IMPORTANT TO IMMUNITY AND REPRODUCTION

by: Stephen B. Blezinger
Ph.D, PAS

Vitamin E was first identified as nutritionally essential for animals about 60 years ago. Rats fed purified diets without vitamin E did not reproduce, plain and simple. Many similar studies have shown similar results in domestic, managed species. From that time, much has been learned about the biochemistry of vitamin E, and the requirements for vitamin E have been established for laboratory animals. Progress in accurately defining the vitamin E requirements of cattle, however, has been slow. The standard method of defining a nutrient requirement is to feed different amounts of the nutrient and measure a certain response that is influenced by the nutrient such as weight gain, cycling activity, etc. The requirement is the point at which an increase in the intake of the nutrient no longer increases the response measured. Application 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 vitamin E requirement of beef cows presents several challenges. Vitamin E intakes are very low (usually less than a few grams per day), and vitamin E concentrations of normal feedstuffs are variable. Therefore, accurately measuring vitamin 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. Because of these and other problems, the true requirements for vitamin E in cattle has not been defined. The vitamin E requirement given by NRC (1989) is largely based on prevention of white muscle disease. 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. This article will discuss vitamin E at length and may be a little more technical than many but understanding the complexity helps understand the importance.

Requirements vs. Recommendations

Before going any farther, 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 vitamin E content of feedstuffs fed to cattle is extremely variable (see below), but the cost of analyzing feeds for vitamin E prevents its routine measurement in feeds. Therefore, the actual vitamin E content of many diets will not be known, and the amount of vitamin 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 vitamin E, toxicity is not a major concern. The National Research Council (NRC, 1987) suggests that ruminants can tolerate intakes of about 40,000 IU/day of supplemental vitamin E for several months without adverse effects (this is 25 to 80 times what is normally supplemented to cattle).

Vitamin E is a relatively expensive nutrient. This cost must be balanced against the cost of not feeding enough vitamin E. As discussed in other research, vitamin E has been shown to reduce the prevalence of retained fetal membranes (retained placenta), reduce clinical mastitis, and improve milk quality and prevent white muscle disease. The estimated cost of one case of retained placenta is $100 to $150 (includes treatment cost and reduced milk and reproductive function.

In dairy cattle a case of clinical mastitis costs approximately $125. White muscle disease usually affects calves and is usually fatal. Increased calf mortality is also costly. Obviously, the cost of feeding inadequate levels of vitamin E can be high.

Vitamin E Content of Feeds

The average concentrations of vitamin E for several feeds are shown in Table 1. As discussed previously, values for vitamin E concentrations really do not have a lot of value because of the large variability in vitamin E concentrations. For example, the coefficient of variation (CV) for vitamin E content of corn grain is 50 percent. The vitamin E content of concentrate feeds is related to the concentration of fat in the feed. 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 vitamin E concentration and tend to reduce the difference in vitamin E content among concentrates. For example, raw soybeans contain substantial amounts of vitamin 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 vitamin E, and vitamin 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 vitamin 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 vitamin E than fresh forage. Also, as with most nutrients, concentrations of vitamin E decrease as forage plants mature.

Effect of Vitamin E on Mastitis-Clinical Data

A major problem in dairy cows that can be effected by vitamin E feeding is mastitis, especially clinical mastitis or infection of the mammary gland. In one of the first studies which examined the effect of vitamin E on mastitis dry cows were fed high forage diets based on hay and silage that provided 0 or 740 IU/day of supplemental vitamin E and were fed no supplemental selenium or injected with 0.1 mg of Se/kg of body weight 21 days before expected calving. (You may recall from previous articles that Selenium and vitamin E affect many of the same systems within the animal and that Selenium actually spares (reduces the need for) vitamin E). Diets fed to lactating cows were not supplemented with vitamin E or selenium. Supplemental vitamin E with or without a Se injection reduced the incidence of clinical mastitis during the subsequent lactation by 37 percent compared with cows not fed supplemental vitamin E or injected with Se. Selenium without supplemental vitamin E reduced the incidence of clinical mastitis by 12 percent compared with un-supplemented cows. Compared with un-supplemented cows, vitamin E without Se injections reduced the duration of clinical mastitis by 44 percent and by 62 percent when Se was injected.

Another clinical trial was conducted by the same group examined the effects of feeding various amounts of vitamin E during the dry period on the prevalence of clinical mastitis during the first week of lactation when all cows were fed .1 mg/kg of diet DM of selenium. In that study cows at dry-off (approximately 60 days before calving) were fed diets with .1 mg/kg of Se and 100 or 1,000 IU/day of supplemental vitamin E. At 14 days before anticipated calving, cows that were fed 1,000 IU/day of supplemental vitamin E either continued to receive 1,000 IU/day or were fed 4,000 IU/day of supplemental vitamin E. Based on concentrations of selenium in whole blood and plasma, all cows were in marginal selenium status. Total intramammary gland infections during the first week of lactation were not different among cows fed 100 or 1,000 IU/day throughout the dry period (30 and 28 percent of lactating quarters, respectively) but cows fed 4,000 IU/day of supplemental vitamin E during the 14-day prepartum period had fewer intramammary gland infections (13 percent of lactating quarters). The incidence of clinical mastitis was 24, 17 and three percent for cows fed 100, 1,000 and 4,000 IU/day of supplemental vitamin E, respectively. The overwhelming majority of available clinical data clearly shows that supplemental vitamin E, above current NRC requirements, reduces the incidence of clinical mastitis.

Assessment of Vitamin E Status of Cows

Plasma concentrations of a-tocopherol (chemical, active form of E) in cows are correlated with intake of vitamin E, but factors other than vitamin E intake can influence plasma a-tocopherol concentrations. Plasma concentrations of a-tocopherol are significantly lower during the peripartum period than during lactation and gestation. The concentration of a-tocopherol in plasma is highly correlated with plasma concentrations of cholesterol with cholesterol concentrations indicative of blood lipid (fat) concentrations. Feeding fat in on or more of several forms to cows increases plasma a-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 vitamin E status in those cows. Another interesting finding is that stress induced from excessive handling, epinephrine or an ACTH injection reduced the concentration of a-tocopherol in plasma of beef cattle. This indicates that newly received or incoming cattle will more than likely have a substandard vitamin 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 a-tocopherol was 2.4 mg/liter. Based on neutrophil function, a cell type primarily involved in immune response, the suggested minimal plasma concentration of a-tocopherol was 3 to 3.5 mg/liter. Low plasma concentrations of a-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 a-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 a-tocopherol and pregnancy rate. Once serum concentrations were greater than 3 mg/liter, no additional improvement in pregnancy rate was observed. Few positive relationships between plasma (or serum) a-tocopherol concentrations and measures of mammary gland health have been found when concentrations are greater than about 4 mg/liter. Based on these data, plasma concentration of a-tocopherol might be useful in assessing vitamin E status of dairy and beef cattle, and current data suggest the concentrations should exceed 3 to 3.5 mg/liter at calving. Minimal acceptable concentrations for other stages of lactation or gestation are not known.

Conclusions

Obviously, vitamin 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.

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 [email protected].