Clinical vitamin deficiency as characterized by classic deficiency symptoms is rare in well-managed dairy herds. Occasionally deficiency symptoms are noted in calves or growing heifers fed poor-quality diets. Of greater concern is the occurrence of sub-clinical vitamin deficiency where classic deficiency symptoms are not observed but where the normal functioning of body systems (i.e., immunity, reproduction, intermediary metabolism) is compromised by marginal vitamin status at the tissue level.

In the past, vitamin status of dairy cattle was assumed to be adequate with routine supplementation of vitamins A and D. Modern research has called this approach into question as studies have shown benefits to animal health and performance from vitamin supplementation over and above minimal requirements and with supplementation of vitamins previously thought to be adequate. For example, the 2001 National Research Council publication Nutrient Requirements of Dairy Cattle made significant changes in recommended levels of supplemental vitamin E for dry and lactating cows.

As with any animal species, dairy cattle have a requirement for essential nutrients like vitamins that can only be obtained from their diet or from production by rumen microorganisms. The question is not whether the cow requires the same vitamins as other species, but whether or not the diets fed to dairy cattle result in optimal amounts of vitamins being absorbed by the cow.

What is optimum? Optimum vitamin supplementation is defined as the level that provides enough of each vitamin to the body organs and tissues to ensure that vitamin supply is not rate-limiting to body functions. This is best illustrated by examples from research. I will focus on three: vitamin E, biotin and vitamin A/beta-carotene in dairy cattle. I will also cover new research regarding vitamin C.

Vitamin E
Vitamin E is essential for the function of a specific class of white blood cells called neutrophils which patrol the blood stream and which are called into tissues like the mammary gland to fight infection. Somatic cell counts (SCC) are primarily a count of neutrophils in milk. Research has shown that the function of neutrophils in the mammary gland is dependent on vitamin E status.

Ohio State researchers reported that feeding 4,000 international units (IU) of vitamin E for 14 days before calving and 2,000 IU per day for the first 100 days of lactation resulted in higher plasma vitamin E and lower incidence of clinical mastitis compared to either 1,000/500 IU per day or 100 IU per day. Cows in this study were fed only 0.1 ppm selenium in their diet, but subsequent studies have found similar benefits of supplementing 3,000 to 1,000 IU per day during pre-fresh and early lactation. Cows were fed 3,000 IU per day vitamin E for four weeks prior to calving and 1000 IU per day for the first four weeks after calving. The NRC recommendation would be 1000 IU and 500 IU during the same period. Control cows did not receive additional vitamin E (see Table 1*).

Although SCC was low in this commercial herd, there was still a benefit of higher levels of supplemental vitamin E for milk quality. Another benefit of vitamin E in this study was a significant reduction of plasmin in milk. Plasmin is a protease enzyme that is elevated by mammary infection and which reduces cheese yield.

All the studies referenced used conventional vitamin E acetate (all-RAC alpha tocopherol acetate) which is the USP standard for vitamin E activity.

Biotin
In higher-producing cows, supplemental biotin has increased milk production, but the beneficial effects of biotin on hoof integrity and health have been observed in cows at all levels of milk production and housing conditions, including pasture. Cows supplemented with a 2 percent spray-dried biotin product showed significant increases in plasma biotin concentration. Reductions in hoof lesions and lameness were observed.

Biotin has been reported to increase milk production of dairy cows in a number of studies. A recent study at Ohio State demonstrated that higher-producing cows, whose metabolic requirement for biotin would logically be higher, respond much more in milk production to 20 mg per day supplemental biotin than low-producing cows. In this study, biotin was supplemented in a 2 percent spray-dried product form.

In the same study, biotin supplementation of high-producing cows also increased the yields of milk fat, protein and lactose. Unlike the effects of biotin on hoof health which require three to six months for turnover of hoof horn tissue, milk production responses occur immediately, indicating that biotin status for metabolic function is marginal in higher-producing cows.

Vitamin A and beta-carotene
Vitamin A is among the most essential of the vitamins, and the body has an elaborate system for the storage and distribution of vitamin A to the tissues. Vitamin A deficiency results in blindness, sterility and failure of immunity. Beta-carotene is the natural precursor of vitamin A, and prior to the advent of commercial sources of vitamin A, this was the primary source of vitamin A activity for dairy cattle. Beta-carotene is converted to vitamin A by being split in two by an enzyme found in the intestinal lining and in the liver. However, this process is not 100 percent efficient and so beta-carotene is also absorbed intact after which it is accumulated in certain tissues like the corpus luteum of the ovary and secreted in milk. Colored dairy breeds absorb more beta-carotene than Holsteins. The corpus luteum (yellow body) is named for its high beta-carotene content.

Beta-carotene has unique antioxidant properties and has been shown to be required for synthesis of progesterone by the corpus luteum. Other studies have found that low beta-carotene status may compromise udder and uterine health around the time of calving. However, the studies with beta-carotene in dairy cattle have yielded mixed results and so it remains unclear when to supplement.

In order for supplemental beta-carotene to be effective there must be a deficiency of beta-carotene at the tissue level, for example in the corpus luteum or the mammary gland. A survey of beta-carotene in blood samples taken during the National Animal Health Monitoring System (NAHMS) study of 1996 revealed large variation in the beta-carotene status of individual dairy herds. This is most likely due to environmental effects and specifically the diet.

Herds with very low levels of plasma beta-carotene, less than 1.5 microgram (ug) per milliliter of plasma or serum, are at greater risk of beta-carotene depletion of the ovary and subsequent reduction in progesterone synthesis and fertility. Another survey conducted in the U.K. found significant seasonal variation in the beta-carotene concentration of corpus lutea collected from cull dairy cattle. Concentrations were lowest in the winter when green forage was not available and when stored forages have lost most of their original beta-carotene content.

While not all studies have found benefits of supplemental beta-carotene in dairy cattle, some recent studies have been more encouraging. In a study conducted in Florida, pregnancy rate was improved by supplemental beta-carotene during heat stress but not during the cooler season. However, supplemental beta-carotene increased milk production in all the experiments probably because of the low content of green forages in the rations.

Another more recent study is a field trial on a commercial dairy in Mexico, conducted during summer heat stress. In this study, the ration was more typical with corn silage, alfalfa hay and concentrate.

In this study feeding 400 mg per day of supplemental beta-carotene for the first 150 days of lactation improved reproductive performance of heat-stressed cows.

Another effect of marginal beta-carotene status in dairy cows is on health disorders at calving. Washington State reported in 1994 that supplemental beta-carotene (300 or 600 mg per day) reduced both the incidence of retained placenta and metritis. Similar results have been reported in cows with very low beta-carotene status in a series of recent field studies in China.

Holstein cows with average production of 13,000 to 18,000 pounds of milk were supplemented with 0, 300 or 500 mg per day beta-carotene from 21 days before calving through 80 days after calving. Vitamin A supply was adequate. The base ration was corn silage, alfalfa hay, grass hay, corn, soybean meal and cottonseed meal. For results, see Table 2*. The source of beta-carotene in these studies was a stabilized 10 percent beadlet formulation.

Vitamin C
Vitamin C is an essential water-soluble antioxidant vitamin, but unlike the other vitamins discussed in this article, vitamin C can be synthesized from glucose by the liver of dairy cows. However, it has been speculated that cows experiencing an energy deficit and faced with a mastitis challenge may benefit from additional vitamin C. A Michigan State study reported that intravenous vitamin C helped cows recover milk production more rapidly after mastitis simulated by endotoxin injection. Others have reported the concentration of vitamin C in plasma and milk is reduced in cows with clinical mastitis.

More recently a study was conducted in which vitamin C in a partially rumen-stable form was fed to dairy cows that later received a simulated mastitis challenge with endotoxin. Vitamin C was fed in a phosphorylated form that had previously been shown by the same researchers to elevate plasma vitamin C in dairy cows. Cows were fed 0 or 30 grams per day of vitamin C from two weeks before calving through 40 days in milk. At 30 days in milk (DIM) the mastitis challenge was conducted.

In the study the response to the mastitis challenge was not as severe as in other studies in terms of clinical signs or loss of milk production. Cows fed vitamin C had a significant reduction in somatic cell count during the first 24 hours after the induced mastitis. Vitamin C is required for normal white blood cell function and may have improved the activity of neutrophils entering the udder. These results suggest vitamin C could be of value in cows treated for mastitis or during transition in herds experiencing a problem with clinical mastitis in fresh cows. PD

References omitted but are available upon request.

Tables omitted but are available upon request to editor@progressivedairy.com.