Desenvolvimento, padronização e comparação de técnicas diagnósticas para avaliação da transferência de imunidade passiva em bezerros | Development, standardization and comparison of diagnostic techniques for assessing transfer of passive immunity in calves

Monitoring Transfer of Passive Immunity (TPI) should be performed on farms because calves are born hypogammaglobulinemic and are dependent on colostrum ingestion to acquire maternal immunoglobulins (Ig). Failure of Transfer of Passive Immunity (FTPI) is related to increased risk of morbidity, mortality, lower calf growth rates, and other impairments. There are several techniques available to evaluate TPI and, in this sense, the objective of the present study was (1) to present a literature review on these techniques; (2) standardize the technique considered the gold standard (reference test), Radial Immunodiffusion (RID), in order to use it in the comparison of TPI evaluation techniques; (3) determine the cutoff points for evaluation of TPI in calves under tropical rearing conditions for total protein on optical refractometry, total protein and Brix on digital refractometry, biochemical analysis for total protein and fractions in automated biochemical analyzer, and the developed technique of sodium sulfite turbidity test using the standardized RID technique and (4) to develop a rapid test based on the modification of the previously described technique of sodium sulfite turbidity test, which allows a dichotomous determination of whether the calf has acquired passive immunity and compare it to other techniques for assessing TPI. For this study, 418 samples of 24 to 48 hour-old calves were evaluated using standardized RID technique, total protein on optical refractometry, total protein and Brix on digital refractometry, biochemical analysis of total protein and fractions on automatic biochemical analyzer for all samples. In addition, to testing 17 concentrations of sodium sulfite solutions. All analyzes were performed in triplicate. Calf mortality and number of treatments were analyzed to determine the cutoff points for the techniques evaluated under calf rearing conditions in tropical climate. The in-house standardized RID technique estimated immunoglobulin concentration, but was not efficient in determining the immunoglobulin G concentration of calf serum samples for the evaluation of TPI. The dosage of globulins was more representative of TPI and should be used as the gold standard technique. Under tropical calf rearing conditions, the cutoff points for Good and Excellent TPI were, respectively, 7.0 g/dL and 9.0 g/dL for Total Protein, 4.8 g/dL and 7.4 g/dL for Globulins and 2.0 g/dL and 3.5 g/dL for IgG. Refractometers overestimated total protein concentrations, requiring an increase in their cutoff or a correction factor for their use. It has been determined that the 13% sodium sulfite concentration should be used in the rapid test for TPI assessment, as it is closest to the cutoff points for Good TPI under tropical calf rearing conditions.

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