A cross-sectional survey of risk factors for the presence of Coxiella burnetii in Australian commercial dairy goat farms.

The largest Australian farm-based outbreak of Q fever originated from a dairy goat herd. We surveyed commercial dairy goat farms across Australia by testing bulk tank milk (BTM) samples using a commercial indirect enzyme-linked immunosorbent assay and two quantitative polymerase chain reactions (PCRs). Of the 66 commercial dairy goat herds on record, managers from 61 herds were contacted and 49 provided BTM samples. Five of the surveyed herds were positive on at least one of the diagnostic tests, thus herd-level apparent prevalence was 10% (95% confidence interval [CI] 4 to 22). True prevalence was estimated to be 3% (95% credible interval: 0 to 18). Herd managers completed a questionnaire on herd management, biosecurity and hygiene practices and risk factors were investigated using multivariable logistic regression. Herds with >900 milking does (the upper quartile) were more likely to be Coxiella burnetii positive (odds ratio = 6.75; 95% CI 1.65 to 27.7) compared with farms with ≤900 milking does. The odds of BTM positivity increased by a factor of 2.53 (95% CI 1.51 to 4.22) for each order of magnitude increase in the number of goats per acre. C. burnetii was not detected in samples from the majority of the Australian dairy goat herds suggesting there is an opportunity to protect the industry and contain this disease with strengthened biosecurity practices. Intensification appeared associated with an increased risk of positivity. Further investigation is required to discriminate the practices associated with an increased risk of introduction to disease-free herds, from practices associated with maintenance of C. burnetii infection in infected dairy goat herds.

Anthelmintic resistance of gastrointestinal nematodes in dairy calves within a pasture-based production system of south West Western Australia.

The objective of this study was to determine the prevalence of gastrointestinal nematodes among post-weaned calves aged between 4 and 12 months old within a pasture-based system of south west Australia and quantify the level of anthelmintic resistance. Pre-treatment FECs were monitored on 14 dairy farms. Anthelmintic resistance was assessed on 11 of the farms. Control FECs were compared with anthelmintic FECs at 14 days post-treatment with doramectin (injectable), levamisole (oral), fenbendazole (oral) and a levamisole/abamectin combination (pour-on). Results demonstrate a strong level of anthelmintic resistance, with at least one class of anthelmintic failing to achieve a 95% reduction in FEC in one or more gastrointestinal nematode species. Doramectin was fully effective against Ostertagia, but C. oncophora displayed resistance in 91% of the farms. Conversely, levamisole was fully effective against C. oncophora, but Ostertagia displayed resistance in 80% of the farms. Fenbendazole resistance was present in both C. onocphora and Ostertagia in 64% and 70% of the farms, respectively. Trichostrongylus showed low resistance, occurring in doramectin (14%) and levamisole/abamectin combination (14%). This study confirms that anthelmintic resistance is common. Regular FEC reduction testing is recommended to monitor and guide decision-making for appropriate anthelmintic usage.

A pilot study on bacterial isolates associated with purulent vaginal discharge in dairy cows in the south-west region of Western Australia.

This study aimed to determine the bacterial isolates associated with postpartum endometritis among dairy cows in Western Australia and their antimicrobial susceptibility profiles. A cross-sectional study was conducted between June-October 2020. Endometritis was defined as evidence of mucopurulent to purulent vaginal discharge 60-100 days postpartum. Vaginal discharge samples were obtained, cultured, identified and tested for antimicrobial susceptibility. A total of 118 bacterial isolates were grown from 46 animals, representing 36 species. The bacteria isolated from both aerobic and anaerobic cultures included Bacillus (60.2%), Streptococcus (12.7%), Trueperella (10.1%), Escherichia (6.7%) and Staphylococcus (5.9%). The remaining genera <5% were Histophilus, Aeroccocus, Enterococcus and Moraxella. Resistance was variable between isolates, but the highest resistance levels were observed in Streptococcal and Bacillus isolates to enrofloxacin, clindamycin and erythromycin, respectively. All Streptococcal isolates exhibited 100% resistance to enrofloxacin, and the greatest resistance levels were found in Streptococcus luteinises to trimethoprim-sulfamethoxazole 83%, clindamycin 66% and 33% quinupristin-dalfopristin. There was 84.5% resistance to clindamycin and 35.2% to erythromycin in the Bacillus isolates, with the highest resistance found in Bacillus licheniformis and Bacillus subtilis. Escherichia coli exhibited 12.5% resistance to gentamycin, ceftiofur, whereas amoxicillin-clavulanic acid exhibited 37.5%. Within the Staphylococcal isolates, 28.5%, 28.5%, 42.8% and 14.2% resistance to ceftiofur, erythromycin, cefoxitin, penicillin and tetracycline were observed, respectively. The presence of resistance to important antimicrobials for human use, such as cephalosporins, macrolides and fluoroquinolones, highlights the need for judicious use of antimicrobials in dairy cattle.

A survey of calf rearing practices in the south-west region of Western Australia.

AIMS: To gather data on the calf management and rearing practices of a subset of dairy farmers in the south-west region of Western Australia. METHODS: A 30-minute face-to-face survey was conducted with dairy cattle producers in the south-west region of Western Australia from April-June 2019 to determine pre-weaning calf rearing practices. Participation was voluntary, using a self-selected subset of dairy farmers registered with a regional extension group. The questionnaire assessed three broad categories: farm demographics, colostrum harvesting and management and calf rearing practices. RESULTS: The study response rate was 34/140 (24%). The following key areas were identified where there were deviations from recognised best practice: Precalving: no transition diet was fed pre-calving on 4/34 (12%) of farms, and on a further 5/34 (15%) it was fed for less than 3 weeks; mixing of heifers and adult cows in the calving paddocks occurred in 24/34 (70%) of the farms, with 15% (5/34) of the farms using calving induction. During calving 14/34 (41%) of the farms did not disinfect navels of new-born calves; although 23/34 farmers stated that they collected calves within 6 hours of birth, data on frequency of calf pick-up (2/34 did not separate calves and dams and 19/34 picked up only once per day) indicated that on 21/34 farms (62%) the reality was that calves were picked up >12 hours after birth. Colostrum quality was not assessed appropriately on 18/34 (53%) farms and farmers overestimated how soon after birth it was administered: 23/34 (68%) reported feeding it within 6 hours of calving, despite 62% picking up calves >12 hours after calving. Regarding calf rearing practices, no pain relief before or after dehorning was used on 20/34 (59%) farms, calf bedding was removed infrequently (

Molecular epidemiology and antimicrobial resistance profiles of Salmonella isolates from dairy heifer calves and adult lactating cows in a Mediterranean pasture-based system of Australia.

Dairy cows can be reservoirs of foodborne pathogens such as Salmonella that pose serious public health risks to humans. The study was designed to examine the molecular epidemiology and antimicrobial resistance profiles of Salmonella isolates from dairy heifer calves and adult lactating cows in the pasture-based system of Australia. A total of 838 animals (328 heifer calves and 510 lactating cows) from 22 farms were sampled. Overall, 54 Salmonella isolates were recovered (calves 28/328 and cows 26/510). A herd-level Salmonella prevalence of 50% (95% confidence interval: 31%-69%) was recorded. Within-herd prevalence for Salmonella ranged between 4%-29% and 4%-45% among the heifer calves and adult lactating cows, respectively. Three different serovars were identified with Salmonella Infantis being the most common serovar (n = 33, 61%) followed by Salmonella Kiambu (n = 20, 37.0%) and one isolate of Salmonella Cerro (2%). The highest antimicrobial resistance prevalence of Salmonella isolates was found against streptomycin (n = 31, 57%), followed by cefoxitin (n = 12, 22%), ceftriaxone (n = 2, 4%), and chloramphenicol (n = 1, 2%). Multiple class resistance was observed on 4 isolates against cefoxitin, chloramphenicol, and streptomycin. Multilocus sequence types ST32 (61%), ST309 (37%), and ST367 (2%) were strongly linked to the serovars Salmonella Infantis, Salmonella Kiambu, and Salmonella Cerro, respectively. Whole genome sequencing of Salmonella isolates detected only 2 resistance genes: aac(6') gene that confers resistance against aminoglycosides among 40.7% of the isolates, and a single isolate positive for the blaDHA-16 gene. Two distinct clusters among the serovars were observed suggesting 2 independent sources of spread. Despite the low prevalence of antimicrobial resistance among Salmonella from the dairy farms, our findings contribute to the regional and national understanding of antimicrobial resistance in dairy herds in Australia. There is need for continued antimicrobial resistance stewardship and surveillance programs to ensure the production of high-quality food products and the long-term protection of both animal and human health.

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.

A descriptive retrospective study on mortality and involuntary culling in beef and dairy cattle production systems of Western Australia (1981-2018).

Identifying and quantifying the relative frequency of involuntary losses is an essential first step in developing fit-for-purpose herd health programmes. The objective of this study was to provide an estimate of the relative frequency of reasons for mortality among south-west Western Australian beef and dairy cattle, based on necropsy findings from a university-based veterinary pathology referral centre over 38 years. A total of 904 cattle were submitted for postmortem examination throughout the study period. Gastrointestinal, cardiopulmonary and reproductive conditions were the most common causes of mortality in cattle submitted for necropsy at Murdoch University for the period 1981-2018. In dairy cattle, the common problems were gastrointestinal (bloat, abomasal displacements) 18% (59/320), cardiovascular (traumatic reticulo-pericarditis) 9% (30/320) and respiratory conditions (pneumonia) 8% (27/320). In beef cattle, the most common conditions were gastrointestinal (bloat, rumen acidosis) 11% (39/358), reproductive (metritis) 11% (38/358), cardiovascular (traumatic reticulo-pericarditis) 7% (25/358), respiratory (pneumonia) 7% (24/358), lameness (fractures) 6%, (21/358) and hepatobiliary conditions (blue-green algae poisoning, hepatotoxicity) 6% (21/358). Selection bias and missing data were potential confounders in this study. Although necropsy investigations provide useful information on animal mortalities and avenues for future herd health programmes, there is a need to standardise data capture methods and disease definition criteria, and conduct more detailed recording of data both at the farm level and at necropsy diagnostic centres.

Cervico-thoracic vertebral subluxation in sheep: Awareness among veterinarians of a rare syndrome.

Cervico-thoracic vertebral subluxation (CTVS) in sheep is a collective term that is used to describe various conditions that concomitantly affect the cervical and thoracic vertebrae, leading to their collapse. The aetiology and pathophysiology of CTVS remain unknown. The objective of this study was to conduct an epidemiological farm investigation and describe the clinicopathological findings of CTVS cases occurring in a flock of sheep; as well as to determine awareness of CTVS among sheep producers and ruminant veterinarians in Australia. Diagnostic imaging revealed severe deformities in the vertebrae between C6-C7 and T1-T3. Sheep affected with CTVS were at a four times higher risk of having low body condition scores (< 2 based on a 5-point scale) compared with non-affected sheep, OR = 3.98, 95% CI (1.20-12.65), p = .02. Survey results revealed that only 34% (15/44) of respondents were aware of CTVS. There is a need to further explore the aetiology and pathophysiology of CTVS, and the impact it has on sheep breeding and production.

Associations between immune competence, stress responsiveness, and production in Holstein-Friesian and Holstein-Friesian × Jersey heifers reared in a pasture-based production system in Australia.

The objectives of this study were to assess antibody and cellular immune responses in first-lactation dairy heifers reared under a pasture-based production system and to investigate associations between immune competence and stress responsiveness, health, and productivity. A commercial vaccine was used to induce antibody and cellular immune responses and, based on measured responses, animals were classified as above average, average, and below average for each trait independently and in combination (overall immune competence). Overall immune competence phenotypic rankings were generated by combining standardized residual values for antibody and cellular responses measured in individual heifers. Cortisol responses to handling and yarding were used to assess stress responsiveness, worm egg counts were used to assess internal parasite burden, somatic cell counts to assess udder health and estimates of total daily milk volume, and milk fat and milk protein contents to assess productivity. A total of 393 Holstein-Friesian and Holstein-Friesian × Jersey crossbred heifers from 2 herds practicing seasonal calving in a pasture-fed production system were enrolled in the study. The immune competence phenotypes of individual heifers were assessed before their first mating and their subsequent performance during their first lactation was monitored. Animals with below-average antibody and cellular immune competence had higher serum cortisol concentrations compared with their counterparts following handling, suggesting they had a reduced ability to cope with management-induced stress. Furthermore, a significant negative (favorable) correlation was observed between antibody responses and stress responsiveness. Similarly, correlations between antibody responses and internal parasite burden were significant and negative (favorable). No correlations were observed between overall immune competence and milk yield, milk fat, and milk protein content.

Periparturient immunosuppression and strategies to improve dairy cow health during the periparturient period.

Common health problems observed during peripartum include milk fever, mastitis, fatty liver disease, ketosis, dystocia, retained placenta, metritis, hypomagnesaemia and abomasal displacements. The increased incidence of health problems observed during the periparturient period can be partly attributed to suboptimal immune responses. Factors contributing to decreased periparturient immunity include the act of parturition itself, impaired leukocytic activity, effects of colostrogenesis and lactogenesis, and associated hypocalcemia and negative energy balance. Nutritional and other management strategies represent a relevant short-term strategy aimed at improving the health and welfare of the transitioning cow. Additionally, it is important to consider improving the health of dairy herds through the genetic selection of animals with enhanced robustness by identifying those with superior disease resistance or resilience in the face of infection. As a consequence these animals are better able to cope with the production and environmental stresses. These may provide long-term selection strategies for improving the health and welfare of the transitioning cow particularly when combined with sound management practices, allowing dairy cattle to reach their full genetic potential.

Assessing adaptive immune response phenotypes in Australian Holstein-Friesian heifers in a pasture-based production system.

The objective of this study was to determine the repeatability of ranking Holstein-Friesian heifers reared in an Australian pasture-based production system for immune responses (IR) when ranking was based on secondary versus tertiary IR. Further objectives were to investigate associations between IR and stress responsiveness, ADG and resistance to internal parasites. A total of 100 heifers were IR phenotyped at 5 to 6 mo of age and again at 12 to 13 mo of age using commercial vaccine antigens to induce measurable IR. Antibody production to tetanus toxoid (TT) was used to assess antibody-mediated IR (AMIR), and delayed-type hypersensitivity reactions to vaccine antigens were used to assess cell-mediated IR (CMIR). Changes in serum cortisol and haptoglobin were used to assess stress responsiveness and fecal egg counts used as a measure of resistance to internal parasites. Based on testing, animals were categorized as either average to above-average (High) or low responders for IR. Secondary and tertiary AMIR were well correlated (r = 0.651, adjusted R(2) = 0.418, P < 0.0001), whereas correlations between secondary and tertiary CMIR were poor (r = 0.078, R(2) = ­0.004, P = 0.450). A Cohen kappa (κ) test of agreement was used to test the consistency of ranking of individual animal for IR and, therefore, the ability to consistently identify low immune responder animals within the herd across test periods. The consistency of ranking (High versus low) was moderately high for AMIR (κ = 0.445), poor for CMIR (κ = ­0.055), and fair to moderate for combined IR (κ = 0.395). High AMIR phenotype animals had significantly higher serum cortisol concentrations than their low immune responder counterparts (P = 0.045). A similar relationship was observed in heifers categorized for CMIR, with High CMIR responders having higher serum cortisol concentrations than their low responder counterparts (P = 0.008). High AMIR calves had a higher ADG compared with low AMIR calves (0.72 ± 0.02 versus 0.66 ± 0.06 kg/d; P = 0.009). Serum haptoglobin concentrations and worm egg counts were very low and could not be used to investigate associations with immune responsiveness. It is concluded that secondary and tertiary antibody responses to TT were well correlated in the Holstein-Friesian heifers in this study and that by using the testing procedure described here, low antibody responders were able to be consistently identified in the herd.