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

Meta-Analysis on the Prevalence of Failed Transfer of Passive Immunity in Calves from Pasture-Based Dairy Farms in Australasia

Monitoring and minimizing the prevalence of failed transfer of passive immunity (FTPI) in dairy replacement calves within the first week of life is crucial for calf health and farm profitability. In this study, a systematic literature search and meta-analysis were conducted on papers reporting the prevalence of FTPI in calves from pasture-based dairy farms in Australia and New Zealand. Two search methods, a "traditional method" and a "search engine method", were conducted to identify published studies on FTPI in Australia and New Zealand. Data from a total of 13,430 calves from eight studies in Australasia were included in the analysis for FTPI within 8 days of birth. The meta-analysis revealed that the average prevalence of FTPI was 33% across the two countries, with the lowest FTPI (9%) in Western Australia and the highest FTPI (59%) in New Zealand. Using farm data from three studies, the average prevalence of FTPI at the farm level in Australasia was 38%, with the lowest prevalence found in a farm in South Australia (6%). In conclusion, the meta-analysis confirmed the need for good management of cows and newborn calves after birth in pasture-based systems to reduce FTPI in calves. Collecting newborn calves from pasture at least twice per day after birth and providing colostrum of sufficient quantity and quality as soon as possible were the best practices for preventing FTPI in Australasian dairy systems.

Incidence of Inadequate Transfer of Passive Immunity in Dairy Heifer Calves in South Australia

The objective of this observational study was to estimate the incidence of inadequate transfer of passive immunity (ITPI) on five pasture-based dairy farms in South Australia. Heifer calf uptake of colostrum was evaluated within the first 1−7 days of age (n = 2638) using a digital refractometer to estimate each calf’s serum total protein concentration, as an indicator of colostrum uptake. Results of <51 g/L indicated inadequate transfer of passive immunity (ITPI). The data showed that the incidence of ITPI on the farms was 6.5%, 31.3%, 48.8%, 49.7% and 52.4%. The incidence of ITPI was calculated in relation to the age of the calf at testing and the breed of calf, and no significant differences were found. A significant difference was found in the incidence of ITPI when comparing the calf’s first feed after separation from the dam (colostrum versus a colostrum-transition milk mixture). The farm with the lowest incidence of ITPI collected calves twice a day, measured colostrum quality on farm with a Brix refractometer and ensured that each calf received an appropriate amount of high-quality colostrum soon after collection. Further studies are required to establish the risk factors of ITPI in South Australian dairy heifers.

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 in; 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%) of 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 by 20/34 (59%) of farms, calf bedding was removed infrequently (<weekly) on 26/35 (76%) of farms and appropriate isolation of sick calves was only reported by 14/34 (41%) of farmers.

CONCLUSION AND CLINICAL RELEVANCE

Although limited by the low response rate, this is the first survey of dairy calf rearing practices in the south-western region of Western Australia. We found evidence of at least one process inconsistent with industry best-practice on 34/140 (24%) of responding farms and all farms had more than one sub-optimal calf rearing practice. This highlights the need to improve calf rearing in this region and identifies key areas of deficiency for further study and extension to producers.

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.