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
Introduction
Calves are born hypogammaglobulinemic and acquire passive immunity through the ingestion of colostral IgG (Larson et al., 1980; Weaver et al., 2000). The lack of or insufficient consumption of IgG results in the failure of passive transfer of immunity (FPTI), defined as serum IgG < 10 mg/mL (Calloway et al., 2002). Important factors that contribute to the successful transfer of passive transfer of immunity (PTI) include ingestion of high quality colostrum with an immunoglobulin concentration > 50 mg/mL of IgG, ingesting an adequate volume of colostrum with at least 150 mg of IgG, prompt ingestion of colostrum within 4 h from birth, and minimising colostrum bacterial contamination (Godden et al., 2019; Weaver et al., 2000). FPTI in calves not only causes significant negative impacts on their early life for instance reduced growth-rate, morbidity and mortality but also has adverse long-term negative effects on reproductive performance and milk production in the first and second lactations (Chuck et al., 2018; Donovan et al., 1998).
Given the benefits of colostrum, investigating the status of PTI in calves ≤7 days old is an important herd health component in dairy production systems. In North America, the prevalence of FPTI in dairy calves ranged from 19% to 37% (Beam et al., 2009; Trotz-Williams et al., 2008). In Australia, a prevalence range of 8% to 42% has been reported but these studies have only included sampling from the intensive dairying regions of the eastern states (Chuck et al., 2017; Phipps, 2016; Vogels et al., 2013). There is a lack of information on this important aspect within the pasture-based dairying regions of Australia such as Western Australia. Dairying in Western Australia is unique with a Mediterranean climate and with larger dairies compared with other states in Australia (Aleri and Laurence, 2020). The objective of this study was to estimate the prevalence of FPTI in the Mediterranean pasture-based dairying region of Western Australian dairies, and to further assess the accuracy of two indirect methods (serum total protein [STP] and brix refractometer) for assessing PTI compared with a direct method of determining serum IgG concentration using the radial immunodiffusion (Vishnu et al., 2015) test.
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Ethics approval
The study was conducted in accordance with the Australian Code of Practice for the Care and Use of Animals for Scientific Purposes, with the approval of the Animal Ethics Committee of Murdoch University (Approval No. R3144/19). Data were collected from April 2019 – June 2019.
Study area
The study was conducted in the south-west region of Western Australia. The region has a temperate Mediterranean climate with an annual rainfall of approximately 730 mm. Dairy farms are predominantly located south-west of
General descriptions
A total of 495 samples from 26 herds were analysed using the three diagnostic tests. The median number of calves selected from each herd was 20 (range 5–25). The majority of the calves were sampled at the age of 7 days (86.1%).The descriptive statistics of the calves included in the study are presented in Table 1.
Overall prevalence of FTPI based on IgG concentration
The overall prevalence of FTPI was 8.7% (95%CI 6.4%–11.6%) by RID with the concentration of IgG detection ranging between 0 and 62.19 μg/ml, and the cut-off for FPTI fixed at
Discussion
As a initial step towards a risk assessment study on calf health and welfare, this study has provided valuable insight on the prevalence of FPTI in dairy herds located in the south-west of Western Australia and assessed the accuracy of two indirect methods for assessing PTI.
To the authors knowledge this is the first study that has provided the prevalence of FPTI in the south-west region of Western Australia. The calf-level prevalence in our study (8.7%) was much lower compared with the findings
Conclusions
From this study, it is concluded that FPTI among pre-weaned dairy calves in south-west Western Australian dairy herds was low with a prevalence of 8.7% and that the brix refractometer was not a reliable indirect method for estimating PTI in calf serum.
Acknowledgments
The study was supported by a grant from Dairy Australia (grant #16085) and partly by Murdoch University (grant #13363). We thank Dr.'s Kathryn Davis, Jo Coombe, John Penry and Stephanie Bullen (Dairy Australia) for their support for this study. We thank John Abbott and Aprille Jack for their technical assistance and the producers for their kind participation in this study.
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