with neutrophils from selenium-deficient cows (Reddy et al. 1986; Hogan et al. 1990; Eicher-Pruiett et al. 1992).
As discussed in Chapter 2, dairy farmers and veterinarians use the presence of immune somatic cells in milk as an indication of the presence of udder infections and mastitis in lactating animals. In 32 Pennsylvania dairy herds, whole-blood concentrations of selenium and activity of the selenium-dependent enzyme glutathione peroxidase (GSH-Px) were higher in herds with low SCCs than in herds with high SCCs (Table 8–3) (Erskine et al. 1987). Herd prevalence of infection was negatively correlated with blood GSH-Px activity, that is, the higher the GSH-Px activity the lower the prevalence of infection. Weiss et al. (1990) also found that plasma selenium and GSH-Px were negatively correlated with bulk tank milk SCC, and the rate of clinical mastitis was negatively correlated with plasma selenium concentration and vitamin E concentration in the diet. These data suggest that general health of animals can be affected by deficiencies in some aspects of nutrition that compromise an animal’s natural ability to fight off invading microorganisms.
Smith et al. (1984) supplemented diets of pregnant heifers with vitamin E (50 to 100 ppm) and selenium (0.3 ppm) 60 days prepartum and throughout lactation. Dietary supplementation reduced staphylococcal and coliform infections at calving by 42.2 percent, and duration of infection by organisms other than Corynebacterium bovis was reduced 40 to 50 percent. Clinical mastitis was reduced in early lactation (57.2 percent) and throughout lactation (32.1 percent), and mean SCC was lower. In addition, injection of 50 mg of selenium 3 weeks prepartum decreased new infections at calving. Likewise, Hogan et al. (1993) observed that dietary selenium supplementation resulted in a more rapid influx of neutrophils into infected mammary glands and increased intracellular killing of ingested bacteria. Dietary supplementation with vitamin E resulted in an increased bactericidal activity of neutrophils.
Vitamin A and its precursor, ß-carotene, are necessary for the proper function of epithelial cell membranes, and they stimulate cellular and humoral immunity. Chew et al. (1982) showed that cows with lower concentrations of vitamin