William P. Weiss
Department of Animal Sciences
OARDC, The Ohio
State University
Wooster, OH 44691
Vitamin E was first identified as nutritionally essential for rats about 60 years ago. Rats fed purified diets without vitamin E did not reproduce. Since that discovery, much has been learned about the biochemistry of vitamin E, and quantitative requirements for vitamin E have been established for laboratory animals. Progress in accurately defining the vitamin E requirements of dairy cows, 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. 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 predicated 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 methods works well, but attempting to define the vitamin E requirement of dairy 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 dairy cows is difficult. Vitamin E can be stored in certain organs (mainly liver), and these stores may mask a short-term vitamin E deficiency. Several weeks or months may be required to deplete cows of vitamin E. Lastly, defining an appropriate response variable to vitamin E is extremely difficult. The response variable usually involves reproductive efficiency or animal health. Long-term studies with large numbers of animals are needed to accurately measure reproductive efficiency and changes in animal health. Because of these problems, the true requirements for vitamin E by dairy cows have not been defined. The vitamin E requirement given by NRC (1989) is largely based on prevention of white muscle disease.
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 environmental 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 dairy cows is extremely variable (see below), but the cost of analyzing feeds for vitamin E precludes its routine measurement in feeds. Therefore, the actual vitamin E content of diets fed to dairy cows 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 dairy cows). Dairy cows probably can tolerate even higher intakes of vitamin E for shorter periods of time (days or weeks).
Vitamin E is a relatively expensive nutrient. Based on typical prices in Ohio, farmers pay approximately 4 to 5 cents per 1000 IU of vitamin E. This cost must be balanced against the cost of not feeding enough vitamin E. As discussed in other papers from this symposium, 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 fetal membranes is $100 to $150 (includes treatment cost and reduced milk production) (Joosten et al., 1988). A case of clinical mastitis costs approximately $125 (Hoblet et al., 1991). White muscle disease usually affects calves and is usually fatal. Increased calf mortality is also costly. Clearly, the cost of feeding insufficient vitamin E can be high.
The current NRC (NRC, 1989) vitamin E requirements of dry and lactating dairy cows is 15 IU/kg of diet dry matter (7 IU/lb. of diet dry matter). This requirement is for total vitamin E, not supplemental vitamin E. Since most diets fed to lactating and dry dairy cows should contain approximately 15 IU of vitamin E/kg, the NRC suggests that cows need essentially no supplemental vitamin E. The cost of feeding vitamin E per NRC requirements, therefore, is about $0. However, based on a survey of dairy nutritionists, the typical diet fed to dry cows in the U.S. provides approximately 900 IU of vitamin E per day and 500 IU per day to lactating cows (Weiss, 1998). The cost associated with feeding these amounts of vitamin E is approximately $9/cow per 365 days. For 100 cows, the cost is $900, which is equivalent to 7 cases of retained fetal membranes or 7 cases of clinical mastitis (or some combination of the two). On a well-managed dairy farm, we would expect approximately 45 cases of clinical mastitis each year per 100 cows. Assuming no other benefits other than reduced clinical mastitis, vitamin E would have to reduce the prevalence of clinical mastitis by 15% to cover the cost of vitamin E supplementation currently practiced in the U.S. Vitamin E supplementation has been reported to reduce clinical mastitis by more than 30%; the $9/cow cost of vitamin E supplementation is justified.
The mean concentrations of vitamin E for several feeds are shown in Table 1. As discussed previously, mean values for vitamin E concentrations have little value because of the large variability in vitamin E concentrations. For example, the coefficient of variation for vitamin E content of corn grain is 50%. 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. Fresh, green forage is an excellent source of vitamin E, and vitamin E concentrations in high quality pasture may exceed 200 IU/kg 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 1 or 2 days before ensiling, and then silage is maintained in an anaerobic 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. As with most nutrients, concentrations of vitamin E decrease as forage plants mature.
A long-term trend in dairy cattle feeding in the U.S. is to use less pasture and more conserved forage, and to feed more concentrate and less forage. Based on the data in Table 1, as silage and hay replace pasture, the intake of vitamin E from the basal diet will decrease. As less forage and more concentrate is fed, intake of vitamin E from the basal diet also will decrease.
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Table 1. Typical vitamin E concentrations of feedstuffs commonly fed to dairy cows. The range in expected values is in parenthesis. |
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|---|---|
| Feedstuff | Vitamin E, IU/kg of dry matter |
| Corn grain | 7 (0-10) |
| Dried distillers grains | 50 (25-75) |
| Oats | 5 |
| Soybean meal | 2 (0-4) |
| Roasted soybeans | 14 |
| Fresh alfalfa | 120 (80-200) |
| Alfalfa hay | 30 (0-80) |
| Alfalfa silage | 60 (10-120) |
| Corn silage | 71 (43-96) |
| Fresh cool season grass | 110 (25-190) |
Limited data are available on the digestibility (absorption) of vitamin E by dairy cows. Tikriti (1969) fed two cows (8 total observations) different amounts of supplemental vitamin E (all-rac-a-tocopheryl acetate) and reported the apparent digestibility (intake-fecal excretion) of vitamin E was 45% (SD=16). The amount of supplemental vitamin E provided (500 to 16,000 IU/day) did not affect apparent digestibility. Alderson et al. (1971) reported that large amounts of vitamin E were destroyed in the rumen and that destruction increased as the amount of grain in the diet increased. More recent studies (Leedle et al., 1993; Weiss et al., 1995) found that essentially no vitamin E was destroyed in the rumen and suggested that poor analytical recovery of tocopherol from digesta was the reason Alderson et al. (1971) reported ruminal destruction.
The most common form of supplemental vitamin E included in dairy cow diets is all-rac-a-tocopheryl acetate. The most important form of vitamin E found in feeds is RRR-a-tocopherol. The USP defines 1 IU of vitamin E as equivalent to 1 mg of all-rac-a-tocopheryl acetate, and 1 IU of vitamin E is equal to 0.67 mg of RRR-a-tocopherol. These conversion factors are based largely on studies with rodents. Based on plasma concentrations of a-tocopherol in cattle, the relative bioactivity of RRR-a-tocopherol may be higher than the USP conversion factor. Hidiroglou et al. (1988) reported that RRR-a-tocopherol was 2.6 times more efficient at elevating plasma a-tocopherol in cattle than was all rac-a-tocopheryl acetate; the USP relative efficiency is 1.49.
The first clinical study on the effects of vitamin E on mastitis was conducted at OARDC by Smith et al. (1984). In that study, dry cows were fed high forage diets based on hay and silage that provided 0 or 740 IU/day of supplemental vitamin E (all-rac-a-tocopheryl acetate) and were fed no supplemental selenium or injected with 0.1 mg of Se/kg of body weight 21 days before expected calving. 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% compared with cows not fed supplemental vitamin E or injected with Se (Table 2). Selenium without supplemental vitamin E reduced the incidence of clinical mastitis by 12% compared with unsupplemented cows. Compared with unsupplemented cows, vitamin E without Se injections reduced the duration of clinical mastitis by 44% and by 62% when Se was injected. Similar results were reported when a study with similar treatments was conducted on first lactation cows (cited by Hogan et al., 1993).
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Table 2. Effect of vitamin E
and selenium on incidence and duration of clinical mastitis (Smith et al., 1984) |
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|---|---|---|---|
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Treatment1 |
Clinical cases | Reduction in clinical cases/ lactating quarter |
Reduction in months clinical/ lactating quarter |
| Control | 33 | 0 | 0 |
| Vitamin E | 21 | 37 | 44 |
| Selenium | 27 | 12 | 46 |
| Vitamin E + Se | 22 | 37 | 62 |
| 1
Control = no supplemental vitamin E or selenium; Vitamin E = 760 IU/day of supplemental vitamin E during the dry period; Selenium = 1 injection of 0.1 mg of Se/kg of body weight given 21 days before calving; Vitamin E+Se = 760 IU/day of supplemental vitamin E plus 1 injection of 0.1 mg/kg of body weight of Se. | |||
Another clinical trial was conducted at OARDC to examine 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 (Weiss et al., 1997). 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 (all-rac-a-tocopheryl acetate). 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% 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% of lactating quarters) (Table 3). The incidence of clinical mastitis was 24, 17 and 3% 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.
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Table 3. Effect of supplemental vitamin E during
the dry period on mammary gland health of dairy cows during the first week postpartum when diets contained .1 mg/kg of selenium (Weiss et al., 1997). |
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|---|---|---|
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Treatment1 |
Intramammary infections % of quarters |
Clinical mastitis % of quarters |
| 100 IU | 31.8a | 25.0a,x |
| 1,000 IU | 32.1a | 16.7a,y |
| 4,000 IU | 11.8b | 2.6b |
| a,b,c Means differ (P
< .05). x,y Means differ (P < .10). 1100 IU = cows fed 100 IU/day of supplemental vitamin E during the dry period (60 days); 1,000 IU = cows fed 1,000 IU/day of supplemental vitamin E during the dry period (60 days); 4,000 IU = cows fed 1,000 IU/day of supplemental vitamin E during the first 46 days of the dry period and 4,000 IU/day during the last 14 days of the dry period. | ||
Plasma concentrations of a-tocopherol in cows are correlated with intake of vitamin E (Stowe et al., 1988; Weiss et al., 1990), 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 (Weiss et al., 1992; Weiss et al., 1994); cholesterol concentrations are indicative of blood lipid concentrations. Feeding fat to dairy cows increases plasma a-tocopherol concentrations in dry cows (Weiss et al., 1994) but not in lactating cows (Atwal et al., 1990). Plasma concentrations of a-tocopherol are less influenced by stage of lactation or gestation and by feeding fat when a-tocopherol concentrations in plasma are expressed per unit of plasma cholesterol. This finding suggests that plasma a-tocopherol per unit of cholesterol or other measure of blood lipid may be a more reliable index of vitamin E status than simply the concentration of plasma a-tocopherol. Stress (excessive handling, epinephrin or an ACTH injection) reduced the concentration of a-tocopherol in plasma of beef cattle (Nockels et al., 1996).
In a study of 50 different herds (544 samples), mean serum concentration of a-tocopherol was 2.4 mg/liter (Miller et al., 1995). Based on neutrophil function (Weiss et al., 1994), 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. 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 (Weiss et al., 1997). Cows with plasma concentrations of a-tocopherol less than 2.5 mg/liter were 2.8 times more likely to have an intramammary infection than were cows with plasma a-tocopherol concentrations greater than 2.5 mg/liter (Weiss et al., 1997). A study with beef heifers (Laflamme and Hidiroglou, 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 cows, and current data suggest the concentrations should exceed 3 to 3.5 mg/liter at parturition. Minimal acceptable concentrations for other stages of lactation or gestation are not known.
Based on the reduction of mastitis following supplementation, the current NRC requirement for vitamin E (15 IU/kg of diet dry matter) is not sufficient. Titration studies have not been conducted, so a specific requirement for vitamin E cannot be accurately determined. In most published studies, the control diet provided three to five times more total vitamin E than the current NRC requirement, yet positive responses usually were observed when additional supplemental vitamin E was provided. Most data suggest that diets for dry cows include between 75 and 90 IU of total vitamin E/kg of diet dry matter, and diets for lactating cows should contain 25 to 50 IU of total vitamin E/kg. Based on expected concentrations of vitamin E in feedstuffs, approximately 1000 IU/day of supplemental vitamin E should be provided to dry cows fed stored forages, and approximately 500 IU/day of supplemental vitamin E should be provided to lactating cows fed stored forages. The amount of supplemental vitamin E can be reduced substantially when cows are consuming considerable amounts of pasture or fresh forage. Based on expected responses, feeding 500 IU/day and 1000 IU/day of supplemental vitamin E to lactating and dry cows, respectively, is economically justified.
Alderson, N.E., J.G.E. Mitchell, C.O. Little, R.E. Warner and R.E. Tucker. 1971. Preintestinal disappearance of vitamin E in ruminants. J. Nutr. 101:655.
Atwal, A.S., M. Hidiroglou, J.K.G. Kramer and M.R. Binns. 1990. Effects of feeding a-tocopherol and calcium salts of fatty acids on vitamin E and fatty acid composition of cow's milk. J. Dairy Sci. 73:2832.
Hidiroglou, N., L.F. Laflamme and L.R. McDowell. 1988. Blood plasma and tissue concentrations of vitamin E in beef cattle as influenced by supplementation of various tocopherol compounds. J. Anim. Sci. 66:3227.
Hoblet, K.H., G.D. Schnitkey, D. Arbaugh and K.L. Smith. 1991. Economic losses associated with episodes of clinical mastitis in nine low somatic cell count herds. JAVMA 199:190.
Hogan, J.S., W.P. Weiss and K.L. Smith. 1993. Role of vitamin E and selenium in host defense against mastitis. J. Dairy Sci. 76:2795.
Joosten, I., J. Stelwagen and A.A. Dijkhuizen. 1988. Economic and reproductive consequences of retained placenta in dairy cattle. Vet Rec. 123:53.
Laflamme, L.F. and M. Hidiroglou. 1991. Effects of selenium and vitamin E administration on breeding and replacement beef heifers. Ann Rech Vet 22:65.
Leedle, R.A., J.A. Leedle and M.D. Butine. 1993. Vitamin E is not degraded by ruminal microorganisms: assessment with ruminal contents from a steer fed a high-concentrate diet. J. Anim. Sci. 71:3442.
Miller, G.Y., P.C. Bartlett, R.J. Erskine and K.L. Smith. 1995. Factors affecting serum selenium and vitamin E concentrations in dairy cows. JAVMA 206:1369.
National Research Council. 1987. Vitamin tolerance of animals. Natl. Acad. Press, Washington, DC.
National Research Council. 1989. Nutrient requirements for dairy cattle. 6th Rev.Eed. Natl. Acad. Sci., Washington DC.
Nockels, C.F., K.G. Odde and A.M. Craig. 1996. Vitamin E supplementation and stress affect tissue a-tocopherol content of beef heifers. J. Anim. Sci. 74:672.
Smith, K.L., J. H. Harrison, D.D. Hancock, D.A. Todhunter and H.R. Conrad. 1984. Effect of vitamin E and selenium supplementation on incidence of clinical mastitis and duration of clinical symptoms. J. Dairy Sci. 67:1293.
Stowe, H.D., J.W. Thomas, T. Johnson, J.V. Marteniuk, D.A. Morrow and D.E. Ullrey. 1988. Responses of dairy cattle to long-term and short-term supplementation with oral selenium and vitamin E. J. Dairy Sci. 71:1830.
Tikriti, H.M. 1969. The metabolism of vitamin E by the lactating dairy cow in relation to oxidized flavor in milk. MS thesis. Univ. of Maryland, College Park.
Weiss, W.P. 1998. Requirements of fat-soluble vitamins for dairy cows: A review. J. Dairy Sci. 81:2493.
Weiss, W.P., J.S. Hogan and K.L. Smith. 1994. Use of a-tocopherol concentrations in blood components to assess vitamin E status of dairy cows. Agri-Practice 15(7):5.
Weiss, W.P., J.S. Hogan, K.L. Smith and K.H. Hoblet. 1990. Relationships among selenium, vitamin E, and mammary gland health in commercial dairy herds. J. Dairy Sci. 73:381.
Weiss, W.P., J.S. Hogan, K.L. Smith, D.A. Todhunter and S.N. Williams. 1992. Effect of supplementing periparturient cows with vitamin E on distribution of a-tocopherol in blood. J. Dairy Sci. 75:3479.
Weiss, W.P., J.S. Hogan, K.L. Smith and S.N. Williams. 1994. Effect of dietary fat and vitamin E on a-tocopherol and B-carotene in blood of peripartum cows. J. Dairy Sci. 77:1422.
Weiss, W.P., J.S. Hogan, D.A. Todhunter and K.L. Smith. 1997. Effect of vitamin E supplementation in diets with a low concentration of selenium on mammary gland health of dairy cows. J. Dairy Sci. 80:1728.
Weiss, W.P., K.L. Smith, J.S. Hogan and T.E. Steiner. 1995. Effect of forage to concentrate ratio on disappearance of vitamins A and E during in vitro ruminal fermentation. J. Dairy Sci. 78:1837.