|dc.description.abstract||Exposure to obligate intracellular Chlamydia abortus and C. pecorum bacteria is ubiquitous in ruminants worldwide, with high seroprevalence rates approaching 100% in some investigations. This study aimed to analyze the effect of these largely asymptomatic infections on the lactating mammary gland of ewes and dairy cows.
C. abortus is the most common abortion agent in sheep. After chlamydial abortion was identified in a flock of milk sheep early in the lambing season, a prospective observational study investigated the progression of the subsequent C. abortus abortion storm in flock. Abortion was associated highly significantly with the gestation phase at high-level exposure to C. abortus during the first abortion in the herd. Abortion sheep showed significantly increased complement-binding antibodies against Chlamydia spp. followed by a highly significant reduction in CFT titers. During the initial seven weeks of lactation, overall milk somatic cell counts in abortion sheep were lower than in live lambing sheep. C. abortus infection of the mammary gland moderately increased milk SCC, but abortion or the anti-chlamydial immune response associated with abortion reduced milk SCC and protected against streptococcal and staphylococcal mastitis.
In dairy cows, mastitis, the inflammation of the mammary gland, is the most prevalent and economically important production disease. To characterize mastitis, caused by natural Chlamydia spp. infection of dairy cows, 17 dairy cows in the second or
higher parity were sampled for 20 weeks after parturition. All cows (100%) were positive for anti-Chlamydia spp.IgM serum antibodies, indicating endemic infection. Twelve (70%) of the cows were PCR-positive for Chlamydia spp. in any of the samples, with 11 cows positive only in vaginal cytobrush specimens, 1 positive only in milk samples, and 2 cows in both types of specimens. Data analysis using principal components resulted in indices “Production loss index”, “Anti-Chlamydia immune index”, and “Inflammatory Index” which delineated the complete dataset in well defined, biologically significant natural clusters. In a multivariate logistic stepwise regression model, cows with chlamydial colonization of the mammary gland had significantly higher milk SCC and lower milk protein. Systemic chlamydial infection highly significantly associated with increased milk yield and milk fat, and decreased milk protein. These data confirm and characterize the influence of asymptomatic localized and systemic chlamydial infection on the health of the mammary gland of dairy cows and their milk production.||en