Interaction of Mastitis and Reproductive Function

Mastitis has been implicated in decreasing reproductive performance of dairy cows. Moore et al. (43) reported a negative correlation between clinical mastitis and reproduction due to altered interestrus intervals and decreased luteal phase length in cows with clinical mastitis caused by Gram-negative pathogens. Cullor (18) suggested that endotoxin might induce luteolysis and influence conception and early embryonic survival by release of inflammatory mediators. Moore and O'Connor (44) hypothesized that Gram-negative mastitis pathogens may stimulate production of prostaglandin F2a which subsequently would cause luteal regression. Barker (3) reported clinical mastitis in the first 150 days in milk has a highly negative effect on services per conception, days to conception, breeding period, and days to first service. University of Florida researchers reported a 2.7 time higher risk of abortion in cows with clinical mastitis in the first 45 days of lactation (54).

There are several plausible means by which increasing zinc status improves udder health. Zinc is important in maintenance of health and integrity of epithelial tissue, such as skin (teats) and mammary tissue, due to its role in cell division and protein synthesis (13). An additional mode of action for zinc reducing SCC is related to zinc's role in keratin formation. Zinc is required for the incorporation of cysteine into keratin (45). The keratin lining of the teat canal entraps bacteria and prevents their upward movement into the mammary gland (16, 47, 48). Approximately 40% of the keratin lining in teat canals of Holstein dairy cattle is removed during the milking process, thus requiring continuous regeneration. Capuco et al. (11) estimated that approximately 1.3 mg of keratin must be regenerated during the inter-milking period.

Zinc deficiencies have been shown to reduce cellular and humoral immune responses (13). Reduced immune function, resulting from a zinc deficiency, is attributed to decreased cell mediated immune response and natural killer cell activity, atrophy of the spleen and thymus, and decreased T-dependent and independent antibody-mediated responses (67).

Results from a study conducted at the University of Missouri lends credence to the theory that reduced SCC is due to increased keratin synthesis and improved immune function (31). The researchers (31) initially collected more keratin from teat canals of cows fed a combination of Zinpro complexed zinc and zinc oxide than cows fed an equivalent amount of zinc in the form of zinc oxide (Figure 10 and Table 4). However, due to the time required to regenerate keratin, there was no difference in amount of keratin collected from cows at subsequent collection time points (31). When cows in this same study were challenged with E. coli, cows fed complexed zinc recovered more quickly from the bout with E. coli mastitis than cows fed zinc oxide, as evidenced in numerically higher milk production and dry matter intake for cows fed complexed zinc (31; Table 4). Prior to the bacterial infection, cows fed complexed zinc produced a similar level of milk as cows fed zinc oxide, but tended to produce milk with a lower SCC (31; Table 4).

Figure 10.