Bacterial pathogens associated with clinical and subclinical mastitis in a Mediterranean pasture-based dairy production system of Australia.

Mastitis is an economically important production disease in the dairy industry worldwide. There is limited information on the aetiology of clinical mastitis (CM) and subclinical mastitis (SCM) in Australia's Mediterranean pasture-based production system. A prospective study was conducted in the south-west region of Western Australia to characterise the bacterial pathogens associated with CM and SCM cases and their associated antimicrobial susceptibility profiles. A total of 102 CM and 132 SCM milk samples were collected in twelve dairy farms between April 2020 and September 2020 recovering a total of 310 bacterial isolates. The isolates were evaluated for their antimicrobial susceptibility to twelve antibiotics using the agar disk diffusion (ADD) method. The most common pathogens associated with CM was Bacillus spp. (35.29%), followed by coagulase-negative staphylococci (CNS) (22.55%), Pseudomonas spp. (19.61%), Staphylococcus aureus (10.78%), Escherichia coli (5.88%) and Streptococcus uberis (2.94%). The most common pathogens associated with SCM was CNS (44.70%), followed by Bacillus spp. (30.30%), S. aureus (20.45%), Strep. uberis (15.91%), coliforms (Citrobacter spp., Cronobacter spp., Enterobacter spp., Klebsiella spp., Kosakonia spp., Morganella spp., Serratia spp.) (9.86%), environmental Streptococci (6.06%) and E. coli (6.06%). Beta-lactams resistance was the most common resistance observed in the Staphylococcal isolates and a high proportion of Streptococcal isolates exhibited resistance to enrofloxacin. Overall, the proportion of bacterial pathogens isolated in this study was comparable to the figures reported in other studies in Australia. Future research should focus on risk factors and the determination of resistant genetic components among the common isolates.

Prevalence of failure of passive transfer of immunity in dairy calves in a Mediterranean pasture-based production system of the south-west region of Western Australia.

The objective of this study was to estimate the prevalence of failure of passive transfer of immunity (FPTI) in dairy calves in the south-west region of Western Australia herds. A cross-sectional study was conducted in 26/140 dairy farms and serum samples were collected from 495 healthy 2-7 day-old calves. A radial immunodiffusion (RID) test was used to determine the concentration of serum IgG and calves were classified as having FPTI if the IgG concentration was less than 10 mg/mL. Estimation of FPTI was also assessed using two indirect methods using serum total protein (STP) and a brix refractometer. The estimated prevalence of FPTI was found to be 8.7% (43 calves out of 495) by RID with the concentration of IgG ranging between 0 and 6.2 mg/ml. The STP was found to vary from 46 to 96 mg/mL and using a cut-off point of 55 mg/mL the calf level prevalence was estimated as 7.1% (33 calves). Using the brix refractometer, the prevalence was found to be 13.1% (65 calves) with the refractometer reading ranging 6-14% of IgG. In the present study there was no association between calf-level factors (age, sex and breed) and FPTI. There was a higher correlation of the RID test results and the STP results compared to the RID and brix refractometer results. It is concluded that the prevalence of FPTI in dairy calves in the south-west region of Western Australia is low (8.7%) and the brix refractometer is not a reliable indirect method for determining passive transfer of immunity to calves.