Two strains of Mycoplasma synoviae from chicken flocks on the same layer farm differ in their ability to produce eggshell apex abnormality.

Mycoplasma synoviae (Ms) is considered to be an economically important poultry pathogen. Although the full economic costs of infection in layer chickens are still under debate, the prevalence of Ms is known to be high in some countries and earlier reports have shown a correlation between infection and Eggshell Apex Abnormality (EAA). This work is a continuation of an earlier study of a clinical case of EAA on a layer hen farm where the presence of two different strains of Ms, based on the sequence of the 5' end of the vlhA gene, was demonstrated. Both strains could be detected in the trachea but only one (designated strain PASC8) appeared able to colonize the oviduct, while the other (designated TRACH) was not found in the oviduct and has not been related to EAA. The PASC8 partial vlhA gene sequence differs from that of the TRACH in having a 39 nucleotide deletion in the proline rich region and three point mutations in the RIII region. Based on this information an experimental infection was performed in SPF chickens using groups infected with either the PASC8 or the TRACH strain and a non-infected control group. Both Ms strains were detected in the trachea of infected birds, but only the PASC8 strain was found in the oviduct. Furthermore, EAA developed only in the group infected with PASC8 strain. Compared to the control group, both strains produced an adverse impact on egg production: a decrease in the numbers laid and in their average weight (P<0.05) This work demonstrates a difference in oviduct tropism between two Ms strains and a possible relationship to the production of EAA in experimental conditions.

Disease risk assessment by clinical immunology analyses in periparturient dairy cows.

A disease prediction system was investigated in a case-control study in the dry period of high-yielding dairy cows. Blood samples of 75 cows from 26 herds were collected before calving between -23 and -33 days (T1) and also between -2 and -6 days (T2) to investigate a panel of clinical immunology and chemistry parameters. Cows with abnormal serum lysozyme and interleukin-6 concentrations showed a greater disease prevalence until the 60th day in milk compared with non-responder cows (P<0.05 and lower at T1). Differences in disease prevalence were observed on the basis of T1 data, and also by combining the results at T1 and T2. The other laboratory parameters under study were not predictive of a disease risk. Results indicate that environmental stressors in the dry period may cause a negative imprinting of the innate immune response, underlying predisposition to later disease occurrence.