Several approaches have been investigated to enhance the resistance of the mammary gland to new infection or reduce clinical severity of the disease. These aproaches should serve a supplemental role to sound nutrition and management and not as their replacement or a ‘quick fix’.
Vaccines
Although previous research on ‘mastitis vaccines’ has met with limited if any success in controlling the disease, immunization studies using a J5 E. coli whole cell bacterin has shown success (Cullor, 1991). Field studies in commercial dairies have demonstrated that the bacterin is safe and efficacious. The incidence of clinical coliform mastitis was approximately 70% less in vaccinated cows compared with those receiving placebo or unvaccinated controls. In addition, vaccinated cows experienced a reduced rate of recurrent infections. Several vaccines against coliforms are available today and are widely used to reduce clinical coliform mastitis at calving. However, successful immunization will remain a useful tool in the control of mastitis and must be only a part of the total management scheme.

Nutrition
The increased interest and research effort in the area of nutritional relationships to host defense has encouraged new and potentially beneficial approaches for enhancing resistance of the dairy cow to intramammary infection by major mastitis pathogens or limiting the severity of response to invasion of the mammary gland when it does occur. Particular emphasis has been made on proper micronutrient nutrition in the dry period, because the time of drying off and the periparturient period are the times when the mammary gland is most susceptible to new infections by the environmental pathogens.
Deficiencies in dietary selenium and vitamin E have been shown to result in increased incidence of mastitis. Supplemental dietary Se and vitamin E were shown to lower the frequency and shorten the duration of clinical mastitis (Smith et al., 1984). A later Ohio study (Smith et al., 1985b) evaluated mastitis incidence in heifers either supplemented with vitamin E and Se or those receiving no supplemental vitamin E and Se from 60 days prepartum and throughout lactation. Prepartum dietary supplementation was with approximately 1000 IU vitamin E per head per day and 2 mg Se per head per day. In addition, supplemented heifers received a subcutaneous injection of Se (sodium selenite) at 21 days prepartum. Lactation supplementation was 600 to 800 IU vitamin E and 2 mg Se per head per day. Vitamin E and Se supplementation resulted in:

1. 42% reduction in prevalence of infection at calving.
2. 57% reduction in clinical mastitis in early lactation and 32% reduction throughout lactation.
3. 40 to 50% reduction in duration of infections.
4. Significantly lower somatic cell counts for the lactation.

Overall, vitamin E and Se improved udder health, and the effect was most evident at calving and early lactation.Another area of micronutrient nutrition that shows potential in this regard is the influence of copper and zinc status on host defense and mastitis. Further, supplementation with copper and zinc proteinates shows promise in improving udder health and somatic cell counts. The reduction in mastitis and lowering somatic cell counts in a dairy herd will result in significant economic benefits as well as improved welfare of the cattle.