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Influence of vaccination on the seroconversion of 2 major respiratory pathogens in German beef rearing farms
Thesing, E.; Vertenten, G.
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Objectives: An important part of the German beef sector is the fattening of Simmental/crossbreed bulls. BRD (Bovine Respiratory Disease) is the main health problem on those farms. The causes are multifactorial, but the contribution of different pathogens is widely accepted. Bovine Respiratory Syncytial Virus (BRSV) and Mannheimia haemolytica (Mh) are 2 major pathogens playing a pivotal role in the BRD complex. Nowadays, the diagnostic of pathogens is mainly done by antigen detection on respiratory samples, rather than serological identification of antibodies. As serological studies during the rearing time in beef calves are not commonly available, a study was performed to obtain insights in the serodynamics of BRSV and Mh using paired blood samples including different BRD vaccination schemes.
Materials & Methods: The study was done on 2 beef rearing farms in different regions of Germany over 2 separate years (2017-2018) during the winter season. All calves were vaccinated with a live intranasal BRSV-Parainfluenza-3 vaccine (Rispoval® RS-Pi3, Zoetis) and received metaphylactic antimicrobial treatment at arrival on the rearing unit. The vaccination protocol was continued with either 2 administrations at 2 and 6 weeks after arrival with a monovalent attenuated vaccine (Rispoval® RS, Zoetis) (control group (cg)) or a multivalent, inactivated BRSV-Parainfluenza-3-Mh vaccine (Bovilis® Bovipast RSP (MSD Animal Health) trial group (tg)). Paired serum samples were taken from relevant subsets of animals in the cg and tg. The first sampling was performed just before the first vaccination and the second sampling 12 weeks later.
BRSV and Mh antibodies were measured in the Centre for Diagnostic Services (MSD Animal Health, Boxmeer, The Netherlands) by in house developed ELISAs and titers were expressed as log2.
Seroconversion for BRSV and Mh was defined as a titer change of 2 log2 steps or more.
A statistical evaluation was done for several parameters with significance level 0.05.
Results: In total 1.127 calves (farm A n=931, farm B n=196) were included in the study. Eventually, paired samples were taken from 196 calves corresponding to approx. 12 % (n=137) of the calves in cg and 5 % (n=59) of the calves in tg.
The baseline serum titers for BRSV and Mh ELISA at the time of the first sampling were not significantly different between groups (p=0.28) and there was no influence of age to the humoral response (p=0.44).
Most calves in the control group showed no humoral response in BRSV titer. Moreover, the titers dropped in a quarter of the calves. Only in 5 calves (4 %) the BRSV -titers increased 4 fold (>2 log2 steps) and consequently identified as a seroconversion. In contrast to this, 58 % of the animals in the trial group seroconverted. If one assumes that the infection pressure is equally high in both groups, one can establish a significant (p<0.0001) better induction of antibody formation after vaccination with the trivalent inactivated vaccine. Apart from the vaccination with the inactivated vaccine, additional field infections might play a role in this seroconversion. A good BRSV response to vaccination with the multivalent inactivated vaccine (Bovilis® Bovipast RSP) has already been described by Berge et al. (2021).
Concerning the Mh antibody induction, 42% of the cg calves had a seroconversion despite the absence of a Mh strain in the administered vaccine. This is indicative for a field infection in those animals. A clear humoral response for Mh under field conditions in young dairy calves is reported also by Jozan (2021). Almost twice the rate (81%) of animals showed serum conversion in the tg (17% > 2 log2 steps; 64% > 4 log2 steps) which is due to the combination of the vaccine effect and the field infection as demonstrated in the cg.
Conclusion: Serological screening of antibodies in beef calf rearing farms provides useful and practical insights into the occurrence of infections and the impact of vaccinations. Interpretation of this data supports the establishment of targeted prophylactic measures. Mannheimia haemolytica is a frequently circulating pathogen in beef calf rearing farms in which the use of a trivalent inactivated BRSV-Parainfluenza-3-Mannheimia haemolytica vaccine (Bovilis® Bovipast RSP) leads to a clear humoral response.
Keywords: Seroconversion, BRSV, Mannheimia haemolytica, vaccination, German beef farms.
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Affiliation of the authors at the time of publication
Intervet Deutschland GmbH, MSD Tiergesundheit, Unterschleißheim, Germany;
MSD Animal Health, Boxmeer, Netherlands.
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