Investigating the role of teat seal in mastitis control: In addition to its effectiveness in preventing mastitis, why is teat seal effective in curing existing cases of mastitis?

The presence of mastitis in bred dairy heifers can adversely affect the development of milkproducing tissues, leading to less than maximal milk production and increased somatic cell counts (SCC) during their first lactation. Use of nonlactating cow therapy has been beneficial in curing existing intramammary infections (IMI), and teat sealants have been beneficial in preventing new IMI from developing. When used together, the combination of the two products may be more effective than either alone in controlling mastitis in these young dairy animals. Recent studies to examine this demonstrated that cure rates after the infusion of nonlactating cow therapy + teat seal, although 96.1% effective, were similar to nonlactating cow therapy alone (100% cure) and teat seal alone (85.7% cure), all of which were significantly (P < 0.001) elevated over untreated controls (55.2% cure); prevention rates ranged between 92.2 and 97.9% for all 4 treatments. Thus, although all 3 infusion treatments were effective in curing existing IMI and preventing new ones, the combination of nonlactating cow therapy + teat seal was not more effective than either treatment alone in controlling mastitis as initially hypothesized. What was unexpected was the 85.7% cure rate (P < 0.001) in quarters infused with teat seal alone. The purpose of the proposed research was to determine why teat seal was effective in curing existing IMI, the results of which may be instrumental in supporting our claims that teat seal is a product that not only prevents new IMI as the product label states, but also cures existing IMI. To accomplish this, mammary secretions were collected at 24, 48, and 72 h after treatment from quarters of heifers randomly assigned to: 1) untreated control, 2) nonlactating cow therapy, 3) teat seal, or 4) the combination of the two products. The SCC, differential leukocyte count, and cytokine activity of secretions were compared among treatments to determine if quarters infused with a treatment that included teat seal, e.g., teat seal alone or teat seal plus antibiotic, elicited an SCC, differential leukocyte, or cytokine response that could be the basis for the elevated cure rate in teat seal-infused quarters that was previously observed. Results demonstrated that the SCC were not different among treatments; however significant changes in differential leukocyte counts and cytokine activity were observed. The percentage of neutrophils increased significantly after all 3 infused treatments and were elevated over controls. Concomitantly, percentages of lymphocytes and macrophages decreased after all 3 infused treatments and were lower than controls. Eosinophil counts were significantly elevated after infusion with the nonlactating cow therapy and the teat seal treatments. Concentrations of tumor necrosis factor alpha (TNF-α) and the ratio of TNF-α to interleukin (IL)-8 were elevated numerically in quarters treated with teat seal compared with other treatments. Results suggest that recruitment of neutrophils into quarters infused with teat seal, as well as the high level of TNF-α in mammary secretions may have provided the antibacterial activity that resulted in the high cure rate after treatment with this infusion product. As observed in previous trials, infusion with nonlactating cow therapy (100% cure), teat seal (87.5% cure), or the combination of the two products (100% cure) were effective in curing existing IMI, and prevention rates ranged between 95 and 100%.