The study assessed three regimes of supplemental vitamin E:
- 100 IU per head daily during the 60-day dry period and first 30 days of lactation (the control group);
- 1,000 IU per head daily during the 60-day dry period and 500 IU per head daily during the first 30 days of lactation;
- 1,000 IU per head daily for the first 46 days of the dry period, 4,000 IU daily for the last 14 days of the dry period and 2,000 IU per head daily during the first 30 days of lactation.
In the cows that received the intermediate level of vitamin E supplementation, the incidence of clinical mastitis was about 30 percent lower than in the control cows. Plasma vitamin E concentrations declined as sharply as in the control group, but the researchers say this result is at odds with earlier studies, in which cows receiving a similar level of supplementation showed a less severe decline in plasma vitamin E levels. This intermediate supplementation level was used in most of the previous Ohio State studies on vitamin E status and mastitis, and the incidence in this study was similar to that in the previous studies. For example,Smith et al. (1984) reported that cows receiving 1,000 IU of supplemental dietary vitamin E per head daily had 37 percent lower incidence of mastitis than controls. The 1984 study also found that among the cows that did contract mastitis, there was 14 percent shorter duration in cows that received vitamin E supplementation. The 1996 study did not measure duration.
Because the Ohio State researchers have conducted only one study using vitamin E supplementation at up to 4,000 IU daily, they are reluctant to change their recommendation that dry cows' rations include supplementation of at least 1,000 IU of vitamin E per head daily and that lactating cows receive at least 500 IU of dietary supplemental vitamin E per head daily.
In economic terms, Weiss et al. (1995) calculated that on an average 100-cow dairy, mastitis costs roughly $5,600 per year. A 30 percent reduction in incidence can save $1,700, and dietary supplemental vitamin E at their recommended levels costs about $600 per year, for net savings of $1,100.
Researchers at the University of Vermont continue to study exactly what the association is between vitamin E status and reduced mastitis. Of particular interest is the ability of white blood cells--especially the polymorphonuclear neutrophils (PMNs)--to respond to infection.
When Escherichia coli and Strep. aureus invade the mammary gland, PMNs migrate to infection sites to engulf and destroy the pathogens. Researchers over the years have reported that both the influx of PMNs into the mammary gland and their killing ability were greater in vitamin E supplemented cows than in unsupplemented cows.
In the summary of a recent study conducted at the University of Vermont, Politis et al. (1996) suggest that the more rapid migration of PMNs into the mammary gland in supplemented cows may be partly due to enhanced ability to penetrate capillary walls and then cross the mammary epithelium. In this work, the researchers measured urokinase plasminogen activators (u-PA), initial components in the processes that allow the PMNs to make their way through the tissues. The researchers reported that total cell-associated u-PA activity was greater in supplemented cows than in unsupplemented cows. The increase was especially great (about 50 percent higher) one week after calving, when the incidence of mastitis is higher and a fast response by neutrophils is needed most.
Supplementation in this study included dietary vitamin E at 3,000 IU per head daily from four weeks before calving through four weeks following it; cows also received a 5,000 IU injection of vitamin E. Control cows received no vitamin E supplementation, but their ration was balanced to meet National Research Council requirements.
This work comes on the heels of a 1995 study (Politis et al.), using the same supplementation regime in which the Vermont researchers measured the strength of the immune response after calving. In that research, the scientists noted a marked decrease in the ability of PMNs and blood macrophages from unsupplemented cows to mount an effective immune response, compared to their precalving response.
The researchers found a 50 percent decrease in the production of superoxide anion by PMNs of unsupplemented cows following calving. This free radical kills invading bacteria and is also associated with the production of even more toxic free radicals. In addition, blood macrophages in unsupplemented cows showed depressed function after calving. They produced 35 percent fewer major histocompatability (MHC) class II antigens and 15 percent less interleukin-1 (IL-1), which is known to activate immunity-mediating T and B lymphocytes.
In supplemented cows, all three immune responses--PMN, MHC and IL-1--remained at precalving levels, and plasma vitamin E levels showed only a slight decline. Vitamin E also appears to work in more generalized ways to affect immunocompetence, notes Ohio State researcher Dr. Larry Smith. For instance, it reduces prostaglandin concentrations in the teat ends. Since high prostaglandin concentrations relax smooth muscle tissue, these could affect closure of the teat ends, decreasing the effectiveness of this primary barrier to invading pathogens. When incorporating vitamin E supplementation into a complete mastitis control program, feeding programs are the most practical option. Although there may be instances when injection is beneficial to achieve a rapid rise in blood levels of vitamin E, any temptation to rely on hasty or last-minute administration will generally prove less satisfactory.
Research is continuing on the effects of supplemental vitamin E in mastitis control.
References:
- Politis, I., et al., 1996. Effects of vitamin E on the plasminogen activation system in bovine neutrophils. University of Vermont (Report).
- Politis, I., et al., 1995. Effects of vitamin E on immune function of dairy cows. Am. J. Vet. Res. 56:179.
- Smith, K.L, et al., 1984. Effect of vitamin E and selenium supplementation on incidence of clinical mastitis and duration of clinical symptoms. J. Dairy Sci. 67:1293.
- Weiss, W.P., et al., 1995. Micronutrients and udder health. Southwest Nutrition and Management Conference. University of Arizona. p. 85.
