Vitamins are organic compounds needed in minute amounts that are essential for life. A vitamin must be in the diet or be synthesized by microorganisms in the digestive system and then absorbed by the host animal. Currently there are 14 recognized vitamins of which four are fat-soluble and ten are water-soluble, 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 U.S. dairy cows) is a clinical deficiency. Marginal deficiencies of vitamins usually have more subtle and less defined signs but can include reduced growth and milk production, poor reproduction and increased prevalence of infectious diseases. The purpose of this paper is to provide an update on new research on vitamins for dairy cows. Research in the past few years has concentrated on water soluble vitamins; therefore those vitamins will be discussed more. However, all cows should be fed supplemental fat-soluble vitamins but not all cows need to be supplemented with water soluble vitamins.
Fat Soluble Vitamins
Although vitamins A, D, and E are essential to cows, not much new information is available on those vitamins. No data are available refuting current recommended (NRC) supplementation rates for vitamins A and D. Because of variability and other unknown factors, diets should be formulated to provide 20,000 to 30,000 IU of vitamin D per day and 85,000 to 100,000 IU/day of vitamin A. Exceeding these rates of supplementation are unlikely to have any positive effect. Some newer information is available regarding vitamin E. The NRC recommends that lactating cows consume about 500 IU/day of vitamin E and dry cows consume about 1000 IU/day. Several experiments have reported that feeding prefresh cows (2 to 3 weeks before calving) more than 1000 IU/day can be beneficial with respect to mammary gland and/or uterine health. Supplementation rates varied among experiments (2000 to 5000 IU/day of supplemental vitamin E), therefore a specific recommendation cannot be determined, but prefresh cows fed hay or silage will probably benefit by supplementing at least 2000 IU/day of vitamin E. Other experiments suggest that prefresh cows that are grazing do not need more than 1000 IU/day and may need even less vitamin E.
Water Soluble Vitamins
We do not know whether cows have an absolute dietary requirement for any of the water soluble vitamins. The liver and kidney of the cow can synthesize vitamin C, and ruminal and intestinal bacteria synthesize most, if not all, of the B-vitamins. The concentrations of many B vitamins are relatively high in many common feeds, therefore, in the vast majority of situations cows do not need to consume any supplemental water soluble vitamins to prevent clinical deficiency. Based on a survey of the highest producing dairy herds in the US conducted in 2000 (Kellogg, 2001) the only water soluble vitamins fed were niacin (43% of the surveyed herds, and choline and biotin (<4% of surveyed herds).
The predominant function of the B-vitamins is to act as co-factors for enzymes that are involved in amino acid, energy, fatty acid, and nucleic acid metabolism (Table 1). Many of these enzymes are involved directly in the production of milk and milk components. Therefore, as milk production increases, the need for these enzymes increase. In the past 15 years, average milk yield per cow has increased from about 14,500 lbs per year to almost 19,500 lbs and herds (not individual cows) that average 28,000 lbs or more per cow are not uncommon. Assuming average milk composition, an average Holstein in 2005 must synthesize approximately 0.4 lbs more milk fatty acids (assuming 50% of milk fatty acids come from the diet), 0.6 lbs more milk protein and 0.9 lbs more lactose each day than the average cow in 1990. During that same period, average dry matter intake has increased from about 44 lbs to about 50 lbs/day. In other words, the yield of milk and milk components has increased about 33%, but dry matter intake has increased only about 15%. Because most B-vitamins are not supplemented, supply to the cow would mostly be a function of intake whereas their need would be a function of milk production. The potential imbalance between supply and need in today’s high producing cow increase the likelihood that responses will be observed when B-vitamins are supplemented.
As with all nutrients, a response to supplementation of B-vitamins will only be observed if supplementation actually increases the supply of vitamin to the tissues that require it. Vitamin supply is the amount (micrograms or milligrams) of a vitamin that is absorbed from the digestive system each day and is a function of the amount of the vitamin consumed, ruminal synthesis and degradation of the vitamin, and absorption by the small intestine.
Ranges in reported concentrations of various B-vitamins in diets fed to lactating cows are in Table 2 (very limited data). Considering the analytical and sampling error usually observed when trace nutrients are measured, concentrations of most of B-vitamins were relatively consistent across the diverse diets with the clear exception of niacin. Niacin concentrations in the diet were positively correlated with the concentration of soyhulls in the diets (i.e., soyhulls had high concentrations of niacin). Additional data are needed to confirm whether soyhulls typically contains such high concentrations of niacin. The biotin concentration of different diets within an analytical method did not vary greatly but method of analysis had a substantial effect (Table 2). Biotin concentrations measured using one analytical procedure averaged about 7 mg/kg and in other studies using a different procedure, it was almost 20 times lower (about 0.4 mg/kg). At the current time, we do not know which method is correct.
For most B-vitamins, flow out of the rumen exceeds intake indicating net synthesis in the rumen (Table 3). With the exception of biotin and vitamin B-6, ruminal synthesis appears to provide the majority of the B-vitamins that reach the small intestine (Table 3). Diet probably affects the amount of B-vitamins produced in the rumen but only one study is available relating diet to vitamin synthesis in dairy cows (Schwab et al., 2006). In that study, generally, diets that were more fermentable (more starch and less fiber) stimulated synthesis of most B-vitamins. The exception was B-12 synthesis which was reduced as starch increased.
Based on limited research, most supplemental B-vitamins are extensively metabolized in the rumen. A study from Wisconsin (Santschi et al. 2005a) reported that approximately 100% of supplemental riboflavin, niacin, and folic acid, 66% of supplemental thiamin and B-12, and about 40% of supplemental B-6 and biotin disappeared in the rumen. For vitamins with high disappearance rates, they must either work in the rumen or they must be protected from rumen degradation if they are to be effective.
Clinical and Production Responses to B-vitamins
Niacin is involved in most energy-yielding pathways and for amino acid and fatty acid synthesis and therefore is important for milk production. Numerous studies have been conducted evaluating the effect of niacin supplementation on milk yield. Schwab et al (2005) combined results from several previous studies and used a new statistical method to evaluate overall responses to niacin. They concluded that supplementing 6 g/d of niacin had no effect on milk production or milk composition. At 12 g/d of supplemental niacin, 3.5% fat-corrected milk increased about 1 lb/d, fat yield was increased 26 g/d and milk protein yield was increased 17 g/d. Based on the current cost of niacin, this response would often not be profitable. The likelihood of a profitable response can be increased by targeting specific animals. Positive responses appear more likely in early lactation, high producing cows and responses are almost never observed in mid and late lactation cows (Girard, 1998). One reason supplemental niacin may not have an effect is that most of it is metabolized in the rumen. A rumen-protected form of niacin is available but published data evaluating the product with dairy cows are not available.
Niacin also has been evaluated as a ketosis treatment and/or preventative but the vast majority of studies show that at rates of 6 to 12 g/d, niacin is not effective at reducing ketosis. Recently, a study from Oregon showed very positive effects when Jersey cows were fed 48 g of nicotinic acid/day from 30 d prepartum until calving but when this study was repeated with Holstein cows, a similar rate of niacin had no effect.
Six clinical trials have been published on the effect of supplemental biotin on hoof horn lesions and lameness in dairy cows (reviewed by Weiss, 2005). Although the response variable 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, and all studies involved long-term (months) biotin supplementation. Biotin supplementation usually reduces hoof lesions in two to three months but six months of supplementation may be required to reduce clinical lameness. The mechanisms by which biotin affects foot health are not well understood.
Milk yield responses to supplemental biotin are less consistent than hoof responses, but the majority of studies reported increased production (Table 4). Low producing cows and/or cows in late lactation are unlikely to increase milk yield when biotin is supplemented. A recent 14-day study from our laboratory found that biotin increased milk yield when supplemented to high-producing dairy cows (control cows average production = 89 lbs/day and 136±56 days in milk), but not when supplemented to low-producing dairy (average production for control cows = 52 lbs/day and 267±53 days in milk). The lack of a production response by low producing cows in that study agree with data from Australia (Fitzgerald t al., 2000). The reason cows in the Rosendo et al. (2004) experiment did not respond is not known (milk production of control cows averaged 79 lbs/day). Across all studies, the median increase in milk yield was 2 to 3 lbs./day. Whereas months of supplementation are required to observe improved hoof health, the milk yield response appears very rapidly (Figure 1). The mechanism by which biotin supplementation increases milk yield is not known, but we have found that supplemental biotin can increase the activity of one gluconeogenic enzyme in the liver of dairy cows.
Other Water Soluble Vitamins
Research is extremely limited on the effects of supplementing other water soluble vitamins to dairy cows. Canadian studies of folic acid supplementation (typical rates are between about 2 and 3 g/day) have produced variable results on milk production. In one study milk production of multiparous cows was increased by 4 to 6 lbs/d when folic acid was supplemented, but no effect was observed with first lactation cows. In other experiments folic acid has not affected milk production. One reason for the variable responses maybe that vitamin B-12 status was limiting. If cows are limited in B-12, they are unlikely to respond to folic acid supplementation. In a study from Wisconsin a mixture of B-vitamins (biotin, folic acid, niacin, pantothenic acid, B-6, riboflavin, thiamin, and B-12) was fed, and milk production was increased compared with the control but was not different from a treatment in which only biotin was supplemented. When the amount of supplemental B-vitamins was doubled, intake and milk production was similar to control cows (i.e., lower than the 1-X supplementation treatment). Shaver and Bal (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. Some experiments with dairy cows have shown some health benefits when vitamin C is injected and other experiments have shown links between vitamin C status and severity of mastitis. At this time, vitamin C for dairy cows is purely experimental. Overall, the available data do not support routine supplementation of ‘other’ B-vitamins or vitamin C. 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. Twelve separate comparisons on effects of feeding rumen-protected choline are available (most were conducted with cows during the first 2 months of lactation). In 7 of the studies, cows fed choline had a statistically significant increase in milk production and in 11 of the studies, milk production was numerically higher when choline was fed. The median increase in milk production when rumen-protected choline was fed was about 5 lbs./day. The cost of rumen protected choline is high but at today’s high milk price, it should be profitable to supplement early lactation cows. In addition to effects on milk production rumen protected choline during the transition period may reduce liver fat but results have not been consistent.
Conclusions and Recommendations
- Feed dry and lactating cows, diets that provide about 25,000 IU/day of vitamin D and 90,000 IU/day of vitamin A.
- During the prefresh period, cows fed silage or hay should be supplemented with 2000 to 5000 IU/day of vitamin E. During the rest of the dry period, 1000 IU/day and during lactation 500 IU/day should be adequate. Grazing cows probably need little vitamin E supplementation.
- Supplemental biotin provided at about 20 mg/day has consistently improved hoof health and increased milk production in several, but not all, studies. For improvements in hoof health biotin must be fed for several months (including the dry period) but increased production will happen within a very short period. Feeding 20 mg/day of biotin to lactating and dry cows is recommended because of its effects on foot health.
- Rumen-protected choline fed at 50 g/day (actual product, not choline) has resulted in increased milk production in most studies and reduced liver fat in some studies. The cost of supplementation is substantial but the median response to supplementation was about 5 lbs of milk/day. 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.
- A milk production response to niacin supplementation at 6 g/day is unlikely, but supplementation at 12 g/d can increase milk production by about 1 lb (likely not a profitable return on investment). A positive return on investment is more likely when supplementation is limited to early lactation cows. The use of supplemental niacin in herds that feed a single diet to all cows is unlikely to have a positive return on investment.
- At this time, insufficient data are available to recommend supplementation of other B vitamins and vitamin C to dairy cows.
Presented at the Tri-State Dairy Nutrition Conference.
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Table 1. Compounds currently recognized as vitamins
Table 2. Concentrations of B-vitamins in cattle diets and typical vitamin intakes by dairy cattle. Data are from 7 different diets fed in 3 experiments (Santschi et al., 2005a; Santschi et al., 2005b; Schwab et al., 2006). All analyses (except where noted) were conducted in a single laboratory.
Table 3. Net ruminal synthesis of B-vitamins by dairy cattle (data derived from (Santschi et al., 2005a; Schwab et al., 2006). Synthesis values are the means of 5 different dietary treatments.
Table 4. Summary of reports on effects of biotin supplementation on milk yield.
Figure 1. Milk yield response when cows in mid (136 days in milk) or late (267 days in milk) were supplemented with 20 mg/day of biotin (Ferreira et al., 2007). Dashed lines represent control cows and solid lines represent supplemented cows. Arrows designate when supplementation started and ended.