Page 66 - Revista Anual - Nº19

industry is faced with the double constraint of limiting Furthermore, the circulating antibody titer at which each
its use of natural resources and antimicrobials whi- virus needed to be below for an individual calf to positi-
le ensuring its economic sustainability. In this context, vely respond to vaccination was determined (log titer of
reliable methods are needed to evaluate the effect of 0.38 for BVDV1, 1.5 for BVDV2, 3.88 for BRSV, and 1.5
the prevention of endemic animal diseases on the pro- for BHV1). This information can be used to improve vac-
ductivity of livestock production systems. In this study,
an epidemiological and productivity model was used to cination protocols to allow for a greater response rate
link changes in Bovine Respiratory Disease (BRD) inci- of individuals to vaccination and, hopefully, improved
dence with the productivity of the beef and dairy cattle protection.
sectors in France. Cattle production parameters signifi- Kramer, LM. et al; J Anim Sci. 2017 Nov;95(11):4820-
cantly affected by BRD were selected through literature 4834.
review. Previous field study results and national cattle
performance estimates were used to infer growth per-
formances, mortality rates and carcass quality in the
cattle affected and not affected by BRD. A steady-state ANTIMICROBIANOS
deterministic herd production model was used to predict
the productivity of the dairy and beef sector and their de-
fined compartments (breeding-fattening, feedlot young
bulls, and feedlot veal) in case of BRD incidence reduc- En Route towards European Clinical Breakpoints
tion by 20%, 50% or 100%. Results suggested that BRD for Veterinary Antimicrobial Susceptibility Testing:
should be controlled at a priority in beef breeding farms A Position Paper Explaining the VetCAST Approach.
as eradication of BRD in beef calves would increase the VetCAST is the EUCAST sub-committee for Veterinary
whole beef sector’s productivity by 4.7-5.5% while era- Antimicrobial Susceptibility Testing. Its remit is to defi-
dication in other production stages would result in lower ne clinical breakpoints (CBPs) for antimicrobial drugs
productivity gain in their respective sectors. However,
the analysis performed at compartment level showed (AMDs) used in veterinary medicine in Europe. This po-
that, in both the beef and dairy sector, young bull and sition paper outlines the procedures and reviews scien-
veal feedlot enterprises derive more economic benefits tific options to solve challenges for the determination
from BRD eradication for their own compartment (in- of specific CBPs for animal species, drug substances
crease in productivity of 8.7-12.8% for beef young bulls) and disease conditions. VetCAST will adopt EUCAST
than the breeding farms (increase in productivity of 5.1- approaches: the initial step will be data assessment;
6% for beef calves), which may limit the investments in then procedures for decisions on the CBP; and finally
BRD control. the release of recommendations for CBP implementa-
Delabouglise, A. et al; PLoS One. 2017 Dec 5;12(12)
tion. The principal challenges anticipated by VetCAST
Evaluation of responses to vaccination of Angus are those associated with the differing modalities of
cattle for four viruses that contribute to bovine res- AMD administration, including mass medication, spe-
piratory disease complex. cific long-acting product formulations or local adminis-
Although vaccination is an effective measure in reducing tration. Specific challenges comprise mastitis treatment
the risk of bovine respiratory disease complex (BRDC) in dairy cattle, the range of species and within species
in cattle, BRDC losses remain significant. Increasing the breed considerations and several other variable factors
efficacy of vaccination depends on elucidating the pro- not relevant to human medicine. Each CBP will be ba-
tective immune response to different antigens included sed on consideration of: (i) an epidemiological cut-off
in vaccines, determining the best timing for vaccination, value (ECOFF) - the highest MIC that defines the upper
and understanding the impact of the age of the calf on
vaccination. This study measured the serum antibodies end of the wild-type MIC distribution; (ii) a PK/PD brea-
present in calves following vaccination against 4 viruses kpoint obtained from pre-clinical pharmacokinetic data
commonly associated with BRDC: bovine viral diarrhea [this PK/PD break-point is the highest possible MIC for
virus type 1 and 2 (BVDV1 and BVDV2), bovine respi- which a given percentage of animals in the target popu-
ratory syncytial virus (BRSV), and bovine herpesvirus 1 lation achieves a critical value for the selected PK/PD
(BHV1). Serum antibody titers were measured in more index (fAUC/MIC or fT > MIC)] and (iii) when possible,
than 1,600 calves at 3-wk intervals starting at the time a clinical cut-off, that is the relationship between MIC
of the first vaccination. This first vaccination occurred at and clinical cure. For the latter, VetCAST acknowledges
weaning for approximately half of the individuals and 3
wk before weaning for the other half. Dam age (years), the paucity of such data in veterinary medicine. When a
time of weaning (initial vaccination or booster vaccina- CBP cannot be established, VetCAST will recommend
tion), and age of calf within year-season (days within use of ECOFF as surrogate. For decision steps, Vet-
year-season) classification all were found to have a sig- CAST will follow EUCAST procedures involving trans-
nificant effect on measured traits such as the initial titer parency, consensus and independence. VetCAST will
and overall response. An increased initial titer was ne- ensure freely available dissemination of information,
gatively correlated with each response trait (initial, boos- concerning standards, guidelines, ECOFF, PK/PD brea-
ter, and overall response). Calves that were weaned at kpoints, CBPs and other relevant information for AST
initial vaccination had greater overall antibody respon- implementation. Finally, after establishing a CBP, Vet-
se to BVDV1 and BVDV2 compared with calves wea-
ned 3 wk before initial vaccination. In contrast, calves CAST will promulgate expert comments and/or recom-
given their initial vaccination 3 wk before weaning had mendations associated with CBPs to facilitate their sou-
greater overall antibody response to BRSV and BHV1 nd implementation in a clinical setting.
compared with calves that were vaccinated at weaning. Toutain, P.L. et al; Front Microbiol. 2017 Dec 15;8:2344.
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