Vitamins are organic compounds needed in minute amounts that are essential for life and must be absorbed from the gastrointestinal tract. Either the vitamin must be in the diet (dietary essential) or be synthesized by microorganisms in the digestive system and absorbed by the host animal. Currently there are 14 recognized vitamins, but not all animals require all 14 vitamins (Table 1). When an animal absorbs an inadequate quantity of a particular vitamin, various responses are observed depending on the vitamin and the degree and duration of deficiency. The most severe situation (seldom observed in the U.S. dairy herd) is a clinical deficiency. For example, rickets and scurvy result from a clinical deficiency of vitamin D and vitamin C, respectively. Marginal deficiencies of vitamins usually have more subtle and less defined signs. Unthriftiness (reduced growth rate, milk production, or fertility) and increased prevalence of infectious diseases can be observed when animals absorb inadequate amounts of vitamins.
Of the 14 known vitamins, only two (vitamins A and E) have absolute dietary requirements for dairy cows. Those two vitamins (or their precursors) must be in the diet, or cows will become clinically deficient. Adequate vitamin D can be synthesized by skin cells when they are exposed to enough sunlight. The liver and kidney of the cow can synthesize vitamin C. Ruminal and intestinal bacteria synthesize most, if not all, of the B-vitamins and vitamin K, and under most situations, cows probably do not need to consume those vitamins to prevent clinical deficiency.
The purpose of this paper is to discuss recent (last 10 years) research on vitamin nutrition of dairy cows. If recent data with ruminants are lacking, the vitamin is not discussed.
Background and What’s New in Vitamins
Vitamin A and β-carotene
The current NRC (2001) requirement for supplemental vitamin A is 50 IU/lb of body weight (BW) or about 70,000 to 77,000 IU/day for an adult cow. β-carotene can be converted into vitamin A but also has biological effects independent of vitamin A. A separate requirement for β-carotene has not been established. Limited data show that vitamin A or β-carotene supplementation of dairy cows may improve mammary gland host defense (i.e., immune function) and may have some positive effects on mammary gland health (Michal et al., 1994).
Some epidemiological data also suggest a link between vitamin A and mastitis (LeBlanc et al., 2004). However (and this is important), there are no data showing that supplementation of vitamin A at rates above the current NRC requirement has any positive effect on mammary gland health or reproductive efficiency; a possible exception is increased ovulation rate when cows are superovulated (Shaw et al., 1995).
|Vitamin A||Gene regulation, immunity, vision|
|Vitamin D||Ca and P metabolism, gene regulation|
|Vitamin K||Blood clotting|
|Biotin||Carbohydrate, fat, and protein metabolism|
|Choline||Fat metabolism and transport|
|Folacin (folic acid)||Nucleic and amino acid metabolism|
|Pantothenic acid||Carbohydrate and fat metabolism|
|Thiamin||Carbohydrate and protein metabolism|
|Pyridoxine (vitamin B6)||Amino acid metabolism|
|Vitamin B12||Nucleic and amino acid metabolism|
|Vitamin C||Antioxidant, amino acid metabolism|
The current requirement for supplemental vitamin E is about 0.3 IU/lb of BW for a lactating cow and 0.7 IU/lb BW for a dry cow. This is equivalent to approximately 500 and 1000 IU/day for lactating and dry cows. Fresh pasture usually contains very high concentrations of vitamin E, and little or no supplemental vitamin E is needed by grazing dairy cows. Although the 2001 requirement was increased substantially compared with the 1989 NRC, newer data suggest that higher supplementation rates may be warranted in some situations. Cows fed 4000 IU of supplemental vitamin E per day during the last two weeks before calving and 2000 IU/day during the first week of lactation had significantly reduced mammary gland infections and clinical mastitis compared with feeding 1000 and 500 IU/day during the dry and early lactation period (Weiss et al., 1997; Figure 1). In that study, cows were fed diets with only 0.1 ppm of supplemental selenium, and that might have affected the response (i.e., a smaller response to vitamin E may have been observed if 0.3 ppm of Se was fed). A study from Italy (Baldi et al., 2000) found that cows fed 2000 IU/d of supplemental vitamin E from two weeks before until one week after calving had significantly lower SCC at seven and 14 days in milk compared with cows fed 1000 IU/d of vitamin E. They also reported fewer services per conception for cows fed the higher amount of vitamin E, but the number of cows in that study was low, and treatment effects on reproductive measures may not be accurate. In two large field studies (Erskine et al., 1997; LeBlanc et al., 2002), injected vitamin E (3000 IU at either 14 or 7 d prepartum) reduced prevalence of retained fetal membranes. Responses were generally more positive for heifers than for cows, possibly because heifers were in lower initial vitamin E status than cows.
A dietary biotin requirement has not been established for dairy cows (or any other ruminant). Most concentrate feeds contain <0.1 mg of biotin/lb of DM. Less is known about biotin concentrations in forages. Data from a very limited number of studies suggest that typical diets fed to lactating dairy cows contain between 0.1 and 0.2 mg of biotin/lb of DM (based on typical dry matter intakes, this equals 4 to 10 mg of biotin/day). Limited in vivo data generally show a small net increase (~1 mg) in flow of biotin out of the rumen compared with biotin intake.
Numerous clinical trials have been conducted to examine the effect of supplemental biotin on hoof horn lesions and lameness in dairy cows (Table 2). Although the response varied among experiments, all studies reported reduced prevalence of specific lesions or clinical lameness when biotin was supplemented. The supplementation rate was 20 mg/d in most studies, but one study with beef cows fed only 10 mg/d and reported a positive response. All studies involved long-term (months) supplementation. Potzsch et al. (2003) reported that six months was required for biotin to reduce the risk of lameness caused by white line disease in lactating cows. Midla et al. (1998), however, reported a significant reduction in white line separation after approximately three months of supplementation. Potzsch et al. measured lameness, but Midla et al. measured lesions, which could be the reason for the difference in the length of time required to see a response.
|0 or 20 mg biotin/d from calving until 300 DIM||Field trial, 1 pen of 1st lactation Holstein cows per treatment||Treatment reduced prevalence of white line separation at 100 DIM||1|
|0 or 10 mg biotin/d for 18 months||Field trial, 1 group of 1- and 2-yr.-old beef heifers per treatment||Treatment reduced prevalence of vertical fissures on claw wall||2|
|0 or 20 mg biotin/d for 13 months||Field trial, 10 farms per treatment (lactating Holstein cows)||Treatment improved locomotion score and reduced prevalence of clinical lameness||3|
|0 or 20 mg/d for 18 months||Field trial, 1 group of lactating Holstein cows per treatment on 5 farms||Treatment reduced prevalence of white line separation||4|
|0 or 40 mg/d for 50 d||Controlled study, 12 nonlactating dairy cows per treatment||Treatment improved healing of sole ulcers||5|
|0 or 20 mg/d for 14 months||Field trial, supplement fed via computer, lactating Holstein cows||Treatment reduced prevalence of sole hemorrhages||6|
|1Citations are: 1) Midla et al., 1998; 2) Campbell et al., 2000; 3) Fitzgerald et al., 2000; 4) Hedges et al., 2001; 5) Lischer et al., 2002; 6) Bersten et al., 2003.|
Six studies have been conducted that measured milk production responses to biotin supplementation (Table 3). The most common treatments were control (no supplementation) and 20 mg of supplemental biotin per day. In studies with higher-producing cows (>75 lb/day), supplementation increased milk production 2 to 7 lb/day in four studies (average response = 3.4 lb/day), but no response was observed in one study. In a study with lower-producing cows (<45 lb/d), biotin supplementation had no effect. Available data suggest that an additional response with supplementation rates greater than about 20 mg/d is unlikely. Milk production response appears to occur shortly after supplementation begins.
|0 or 20 mg biotin/d from calving until 300 DIM||Field trial, 1 pen of 1st lactation Holstein cows per treatment||Treatment increased 305 d ME by 682 lb (P < 0.05). Control ME = 25,900 lb||1|
|0 or 20 mg biotin/d for 13 months||Field trial, 10 farms/trt (lactating Holstein cows)||No effect on milk yield. Yields were 42 lb/d for control and 40 lb/d for treatment||2|
|0 or 20 mg/d for 14 months||Field trial, supplement fed via computer, lactating Holstein cows||Treatment increased 305 d milk by 1058 lb (P < 0.05). Control milk = 22,200 lb||3|
|0, 10, or 20 mg/d from 14 d before through 100 days after calving||Controlled study, 15 Holstein cows/trt, first 100 d of lactation||Linear (P <0.05) effect. 81, 83, and 87 lb/d for 0, 10, and 20 mg||4|
|0 or 20 mg/d for 28 d periods||Latin square, 24 obs./trt, early lactation Holstein cows||Treatment increased milk 2.2 lb/d (P < 0.05). Control milk = 82 lb/day||5|
|20 or 40 mg/d for 28 d periods||Latin square, 24 obs./trt, early-lactation Holstein cows||No difference in milk production between treatments. Average production = 90 lb/d||5|
|0 or 30 mg/d from calving until 70 days in milk||Controlled study, 18 and 20 cows/trt||No difference in 4% fat-corrected milk (77 vs. 76 lb)||6|
|1Citations are: 1) Midla et al., 1998; 2) Fitzgerald et al., 2000; 3) Bersten et al., 2003; 4) Zimmerly and Weiss, 2001; 5) Majee et al., 2003; 6) Rosendo et al., 2004.|
No requirement for dairy cows has been established for niacin, but niacin is involved in most energy-yielding pathways and for amino acid and fatty acid synthesis and therefore is important for milk production. Niacin has also been evaluated for possible prophylactic and therapeutic effects on ketosis and fatty liver syndrome. Although a few studies reported that niacin supplementation during the periparturient period (usually 6 to 12 g/day) reduced blood ketones and plasma nonesterified fatty acids (NEFA), the vast majority of studies show no effect (see page 171 of NRC, 2001 for listing of the studies).
The NRC (2001) also summarized experiments that measured milk yield responses to supplemental niacin (supplementation rates were usually 6 to 12 g/day). Of the 30 studies examined, only one reported a statistically significant (P < 0.05) increase in milk production, and 29 reported no statistical effect. Since the NRC was published, two additional studies were published, and one (Drackley et al., 1998) reported an increase in milk yield, and one (Minor et al., 1998) reported no effect. Although most studies report no statistical effect on milk production with niacin supplementation, the average numerical increase in milk yield is about 1 lb/day when niacin is supplemented. In another review of niacin (Girard, 1998), experiments were classified based on stage of lactation (Table 4). In about 60% of the studies with early-lactation cows, niacin increased or tended to increase milk yield (average response was 6% or 3 to 5 lb/day). In mid- and late lactation cows, niacin supplementation usually did not affect production. Based on this, niacin supplementation would likely be profitable if limited to early-lactation cows, but return on investment would decrease markedly if niacin was supplemented to the entire herd.
|No. of studies||Mean increase||Range in responses|
|Significant increase||3||6.7%||4 to 10%|
|Increase trend||5||6.3%||3 to 9%|
|Significant increase||3||3.9%||2 to 7%|
Research is extremely limited on the effects of supplementing B-vitamins other than biotin and niacin to dairy cows. Milk production was increased when cows were fed a mixture of B-vitamins (biotin, folic acid, niacin, pantothenic acid, B-6, riboflavin, thiamin, and B-12) compared with cows not fed supplemental B-vitamins but was not different from a treatment in which only biotin was supplemented (Majee et al., 2003). When the amount of supplemental B-vitamins was doubled, intake and milk production were similar to control cows (i.e., lower than the 1-x supplementation treatment). In three experiments, Shaver et al. (2000) examined the effects of supplemental thiamin on milk production. In one experiment, yield of milk, milk fat, and milk protein increased when cows were fed 150 mg of thiamin per day. In two other experiments, cows fed thiamin at 300 mg/day had similar milk yields as control cows. Milk yield by multiparous cows increased linearly as supplemental folic acid was increased from 0 to 1.2 or 2.4 g/day, but no response was observed with first lactation animals (Girard and Matte, 1998). Responses to folic acid may be caused by increased methionine status. Injections of riboflavin (2.5 mg/kg of BW) improved neutrophil function and reduced SCC in cows with intramammary infections of Staphylococcus aureus but did not affect cure rates (Sato et al., 1999). At this time, data do not support routine supplementation of "other" B-vitamins. However, as productivity of cows continues to increase and as new experiments are conducted, this conclusion may change.
Choline does not fit the definition of a vitamin. It is required in gram quantities (not milligram or microgram quantities), and it is synthesized by the cow. Very little, if any, dietary choline (with the exception of rumen-protected supplements) is absorbed from the gut because it is degraded in the rumen. Milk yield responses to supplemental choline (either fed in a rumen-protected form or infused post-ruminally) are inconsistent, with about 50% of the studies reporting a positive response and 50% reporting no effect (Donkin, 2002). Supplemental choline during the transition period may reduce liver fat, but results have not been consistent. Rumen-protected choline may have a greater effect on liver fat in over-conditioned cows (BCS > 3.75). Because choline can be synthesized from methionine, diets that provide marginal amounts of metabolizable methionine may be more likely to respond to choline supplementation.
Vitamin C also is not considered a vitamin for dairy cows because the cow can synthesize ascorbic acid. Vitamin C is probably the most important water-soluble antioxidant in mammals. Most forms of vitamin C are extensively degraded in the rumen; therefore, the cow must rely on tissue synthesis. The concentration of ascorbic acid is high in neutrophils and increases as much as 30-fold when the neutrophil is stimulated. Santos et al. (2001) reported that plasma ascorbic acid concentrations in dairy cows were not correlated with SCC; however, the range in SCC was limited (67,000 to 158,000/ml), and cows were only sampled once. Injecting cows that received an intramammary challenge of endotoxin with vitamin C (25 g IV at 3 and 5 hours post-challenge) had limited positive effects on clinical signs (Chaiyotwittayakun et al., 2002). We recently conducted an experiment to examine changes in ascorbic acid status following an intramammary challenge with E. coli (Weiss et al., 2004). Large decreases in vitamin C status were statistically related to longer duration of clinical mastitis, and larger decreases in milk production following challenge were associated with larger decreases in vitamin C status (Figure 2). Data from this experiment do not mean that increasing vitamin C status of cows will reduce the prevalence or severity of mastitis. We do not know whether lower vitamin C status allowed severity of mastitis to increase or whether increased severity depleted body vitamin C. More data are needed before the use of vitamin C to prevent or help cure mastitis can be recommended.
Although the word "requirement" was used liberally in the above discussion, that word implies a much greater knowledge base regarding vitamin nutrition than is actually available. We know very little regarding vitamin flow out of the rumen and even less regarding efficiency of absorption of vitamins from the gastro-intestinal tract of cows. Indeed, most studies with ruminants designed to evaluate responses to vitamins do not even report vitamin concentrations in the basal diet. Undoubtedly, vitamin supply (dietary and ruminal synthesis) is affected by basal diet, dry matter intake, and numerous other factors, and the supply of vitamins from the basal diet will affect the response to vitamin supplementation. Without reliable data regarding vitamin supply from basal diets (i.e., control diets), actual requirements cannot be determined.
For ration formulation purposes, knowing the true requirement for vitamins is not essential. The question that needs to be asked is: What vitamins should be supplemented and at what rates? Good animal husbandry requires that diets be formulated to provide enough vitamins to prevent clinical deficiencies. Following NRC (2001) guidelines (i.e., supplementing diets with vitamins A, D, and E and providing no supplemental water-soluble vitamins) will prevent essentially all clinical signs of vitamin deficiencies. Some unique situations may require special supplementation to prevent clinical signs (for example, supplemental vitamin K should be provided when cows are fed moldy sweet clover hay). The NRC guidelines should be the starting point when developing a vitamin nutrition program.
Determining whether vitamins should be supplemented at rates exceeding NRC should be based on expected benefits compared with the expected costs. The effect of increased vitamin supplementation on feed costs can be determined easily. Few studies show marked effects on feed intake when vitamins are supplemented; therefore, the increased feed costs associated with vitamin supplementation is dependent on the price of the vitamins. Increased supplementation of vitamins will cost from < 1 cent/day per cow (vitamin A and D) to 30 or 40 cents/day (rumen-protected choline). At typical supplementation rates, vitamin E and most common B-vitamins will cost between 5 and 10 cents/day per cow. Excessive supplementation also may incur a cost by having negative effects on health and productivity (true toxicity can also occur, but generally vitamin intakes have to be extremely high). For example, Majee et al. (2003) observed a quadratic effect of B-vitamin supplementation on feed intake and milk production by dairy cows. Benefits of supplementing vitamins in excess of NRC recommendations may include improved health, increased production, and improved reproduction. The economic return of these benefits usually is much greater than the impact of vitamin supplementation on feed costs.
Vitamins A and D: Very little data are available showing any positive effects at rates higher than NRC (approximately 70,000 IU/day for A and 20,000 IU/day for D), but because vitamin A and D are inexpensive and because of some possible (but not highly likely) benefits, oversupplementation is advisable. A safety factor of 20 to 40% should be adequate. Therefore, diets that provide an average of 84,000 to 100,000 IU of vitamin A/day should be adequate for dry, prefresh, and lactating cows. Cows that are grazing probably can be fed substantially less supplemental vitamin A. Diets that provide an average of 24,000 to 28,000 IU/day of vitamin D should be adequate.
Vitamin E: Data showing positive effects when vitamin E is supplemented to lactating dairy cows at rates exceeding NRC are not available. Limited data are available showing positive responses when peripartum cows are fed vitamin E at rates above NRC. Diets for lactating cows >15 to 30 days in milk should provide an average of about 500 IU/day, and diets for dry cows <265 days of gestation should provide approximately 1000 IU/day. Cows during the last 14 days of gestation and the first two to four weeks of lactation may benefit from consuming 2000 to 4000 IU of vitamin E/day. Cows consuming a substantial amount of fresh forage probably need little supplemental vitamin E.
Biotin: Substantial data are available showing improved hoof health when cows are fed 20 mg of biotin/day, and more limited data show increased milk production. Herds with hoof problems will likely benefit from biotin and should be fed diets (all stages of lactation and gestation) that provide 20 mg/day of supplemental biotin. High-producing herds are likely to see an increase in milk production.
Choline: Rumen-protected choline fed at 50 to 60 g/day (actual product, not choline) has resulted in increased milk production and reduced liver fat in some studies, but the cost of supplementation is substantial. A response in milk production is most likely in early lactation (up to about 60 days in milk), and to maximize the likelihood of a profitable return on investment, supplementation should be limited to early lactation cows. Choline supplementation may reduce the risk of ketosis and fatty liver in over-conditioned dry cows, and the use of choline is probably warranted in that situation.
Niacin: A positive return on investment is likely when early-lactation cows are fed approximately 6 g/d of supplemental niacin. Little benefit would be expected when mid- and late-lactation cows are fed supplemental biotin. The use of supplemental niacin in herds that feed a single diet to all cows is unlikely to have a positive return on investment.
Other vitamins: At this time, insufficient data are available to recommend supplementation of other B-vitamins and vitamin C to dairy cows.
The Ohio State University
Baldi, A., G. Savoini, L. Pinotti, E. Monfardini, F. Cheli, and V. DellOrto. 2000. Effects of vitamin E and different energy sources on vitamin E status, milk quality and reproduction in transition cows. J. Vet. Med. (Ser. A). 47:599-608.
Bergsten, C., P.R. Greenough, J.M. Gay, W.M. Seymour, and C.C. Gay. 2003. Effects of biotin supplementation on performance and claw lesions on a commercial dairy farm. J. Dairy Sci. 86:3953-3962.
Campbell, J.R., P.R. Greenough, and L. Petrie. 2000. The effects of dietary biotin supplementation on vertical fissures of the claw wall in beef cattle. Can. Vet. J. 41:690-694.
Chaiyotwittayakun, A., R.J. Erskine, P.C. Bartlett, T.H. Herdt, P.M. Sears, and R.J. Harmon. 2002. The effect of ascorbic acid and L-histidine therapy on acute mammary inflammation in dairy cattle. J. Dairy Sci. 85:60-67.
Donkin, S.S. 2002. Rumen-protected choline: potential for improving health and production in dairy cows. Tristate Dairy Nutr. Conf., Ft. Wayne, Ind. pp. 55-65.
Drackley, J.K., D.W. LaCount, J.P. Elliott, T.H. Klusmeyer, T.R. Overton, J.H. Clark, and S.A. Blum. 1998. Supplemental fat and nicotinic acid for Holstein cows during an entire lactation. J. Dairy Sci. 81:201-214.
Erskine, R.J., P.C. Barlett, T. Herdt, and P. Gaston. 1997. Effects of parenteral administration of vitamin E on health of periparturient dairy cows. J. Amer. Vet. Med. Assoc. 211:466-470.
Fitzgerald, T., B.W. Norton, R. Elliott, H. Podlich, and O.L. Svendsen. 2000. The influence of long-term supplementation with biotin on the prevention of lameness in pasture-fed dairy cows. J. Dairy Sci. 83:338-344.
Girard, C.L. 1998. B-complex vitamins for dairy cows: a new approach. Can. J. Anim. Sci. 78 (Suppl. 1):71-90.
Girard, C.L., and J.J. Matte. 1998. Dietary supplements of folic acid during lactation: effects on performance of dairy cows. J. Dairy Sci. 81:1412-1419.
Hedges, J., R.W. Blowey, A.J. Packington, C.J. O'Callaghan, and L.E. Green. 2001. A longitudinal field trial of the effect of biotin on lameness in dairy cows. J. Dairy Sci. 84:1969-1975.
LeBlanc, S.J., T.F. Duffield, K.E. Leslie, K.G. Bateman, J. TenHag, J.S. Walton, and W.H. Johnson. 2002. The effect of prepartum injection of vitamin E on health in transition dairy cows. J. Dairy Sci. 85:1416-1426.
LeBlanc, S.J., T.H. Herdt, W.M. Weymour, T.F. Duffield, and K.E. Leslie. 2004. Peripartum serum vitamin E, retinol, and beta-carotene in dairy cattle and their associations with disease. J. Dairy Sci. 87:609-619.
Lischer, C.J., U. Koller, H. Geyer, C. Mulling, J. Schulze, and P. Ossent. 2002. Effect of therapeutic dietary biotin on the healing of uncomplicated sole ulcers in dairy cattle - a double-blinded controlled study. Vet. J. 163:51-60.
Majee, D.N., E.C. Schwab, S.J. Bertics, W.M. Seymour, and R.D. Shaver. 2003. Lactation performance by dairy cows fed supplemental biotin and a B-vitamin blend. J. Dairy Sci. 86:2106-2112.
Michal, J.J., L.R. Heirman, T.S. Wong, B.P. Chew, M. Frigg, and L. Volker. 1994. Modulatory effects of dietary B-carotene on blood and mammary leukocyte function in periparturient dairy cows. J. Dairy Sci. 77:1408-1421.
Midla, L.T., K.H. Hoblet, W.P. Weiss, and M.L. Moeschberger. 1998. Supplemental dietary biotin for prevention of lesions associated with aseptic subclinical laminitis (pododermatitis aseptica diffusa) in primiparous cows. Amer. J. Vet. Res. 59:733-738.
Minor, D.J., S.L. Trower, B.D. Strang, R.D. Shaver, and R.R. Grummer. 1998. Effects of nonfiber carbohydrate and niacin on periparturient metabolic status and lactation of dairy cows. J. Dairy Sci. 81:189-200.
National Research Council. 2001. Nutrient Requirements of Dairy Cattle. 7th rev. ed. Natl. Acad. Press, Washington, D.C.
Potzsch, C.J., V.J. Collis, R.W. Blowey, A.J. Packington, and L.E. Green. 2003. The impact on parity and duration of biotin supplementation on white line lameness in dairy cattle. J. Dairy Sci. 86:2577-2582.
Rosendo, O., C.R. Staples, L.R. McDowell, R. McMahon, L. Badinga, F.G. Martin, J.F. Shearer, W.M. Seymour, and N.S. Wilkinson. 2004. Effects of biotin supplementation on peripartum performance and metabolites of Holstein cows. J. Dairy Sci. 87:2535-2545.
Santos, M.V., F.R. Lima, P.H.M. Rodrigues, S.B.M. Barros, and L.F.L. daFonseca. 2001. Plasma ascorbate concentrations are not correlated with milk somatic cell count and metabolic profile in lactating and dry cows. J. Dairy Sci. 84:134-139.
Sato, S., H. Hori, and K. Okada. 1999. Effect of vitamin B-2 on somatic cell counts in milk of clinical Staphylococcus aureus mastitis. J. Vet. Med. Sci. 61(5):569-571.
Shaver, R.D., and M.A. Bal. 2000. Effect of dietary thiamin supplementation on milk production by dairy cows. J. Dairy Sci. 83:2335-2340.
Shaw, D.W., P.W. Farin, S.P. Washburn, and J.H. Britt. 1995. Effect of retinal palmitate on superovulation rate and embryo quality in superovulated cattle. Theio. 44:51-58.
Weiss, W.P., J.S. Hogan, and K.L. Smith. 2004. Changes in vitamin C concentrations in plasma and milk from dairy cows after an intramammary infusion of Escherichia coli. J. Dairy Sci. 87:32-37.
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. 80:1728-1737.
Zimmerly, C.A., and W.P. Weiss. 2001. Effects of supplemental biotin on performance of Holstein cows in early lactation. J. Dairy Sci. 84:498-506.