Reproductive pathophysiology of lactating jersey Friesian vaccinated with prototype killed vaccine and challenged with virulent Staphylococcus aureus via intra mammary route

Reproductive efficiency is one of the most significant determinants of profitability in the dairy industry. Over decades, reproductive efficiency in dairy cattle has declined across the world. Mastitis is one of the most prevalent diseases of dairy cattle, causing economic losses due to reduced productivity. Staphylococcus aureus a major pathogen causing subclinical or clinical mastitis, is a significant contagious cause of the disease in dairy farms in Malaysia. Despite the repetitive use of antibiotics in dairy cows treatment, so far, antibiotic-resistant cases of mastitis persist in Malaysia, necessitating alternative control strategies. Vaccines are convenient way to control or eradicate the disease. Therefore, the present study opined to develop an alum adjuvanted prototype killed mastitis vaccine using a local S. aureus isolate to confine the mastitis reproductive and economic losses. It was presumed that the prepared prototype vaccine would provide satisfactory protection against the reproductive consequences. Hence, the effectiveness of the vaccine was assessed by evaluating reproductive hormone levels and histopathological changes in vaccinated cows experimentally challenged with S. aureus. The current study was conducted on nine (9) healthy lactating Friesian cows, grouped in A (Vaccinated group), B (Positive control group), and C (Negative control group), consisting of three cows in each group. The vaccinated group received the prototype mastitis vaccine, while the positive and negative control groups were inoculated with PBS. A booster dose with the same inoculations after 21 days, and cows in groups A and B were subsequently challenged with virulent S. aureus. The experimental animals were observed for clinical manifestations, and cytokines and reproductive hormone levels were evaluated throughout the study. After 14 days post-challenged, tissue samples were collected for Polymerase Chain Reaction (PCR) and histopathological analyses. Results showed significantly (p ≤ 0.05) higher concentrations of IL-2 and IL-8 in the vaccinated group compared to the controls post-booster vaccination and post-challenge periods. No significant (p ≥ 0.05) differences in serum concentrations of estrogen, progesterone, FSH, and LH were observed among the groups after vaccination. However, significantly (P ≤ 0.05) declined concentrations of these hormones were measured in positive control group post-challenged period compared to vaccinated & negative control groups. Significant histopathological changes were observed in the positive control group, including inflammatory cell infiltration, congestion of blood vessels, degeneration, necrosis, and traces of edema in mammary glands, supra- mammary lymph nodes, and reproductive organs. Organisms harvested from the affected tissues were confirmed and matched with the challenged strain of S. aureus through conventional PCR protocol. Overall, the positive control group showed significant alterations in reproductive histology and hormonal patterns compared to the vaccinated and negative control groups. These findings suggest that the prototype vaccine used in this study protected the animals from mastitis and provided effective efficacy in mitigating the mastitis-related reproductive consequences in dairy cows.

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