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Equine veterinary journal2024; 57(4); 898-903; doi: 10.1111/evj.14421

Colostrum conductivity, pH and Brix index as predictors of passive immunity transfer in foals.

Abstract: Foal immunity relies heavily on the absorption of colostrum immunoglobulins; thus, colostrum evaluation is used to predict the transfer of passive immunity (TPI), and its conductivity is associated with TPI in cattle. Leading up to and at parturition, a reduction in colostrum pH and conductivity is thought to be necessary for TPI; however, this remains to be determined. Objective: To assess conductivity, pH, and Brix refractometer index of colostrum to predict the TPI in foals. Methods: Field study. Methods: The colostrum of 241 mares was assessed for conductivity, pH, and Brix index using handheld devices immediately after parturition. Twenty-hour postpartum foals had complete blood cell count and plasma IgG concentrations assessed. Foals were split in complete versus incomplete TPI (i.e., IgG ≥8 g/L vs. <8 g/L). Mare (breed, duration of pregnancy, parity, and age), foal (sex), and colostrum (conductivity, pH, and Brix index) data were computed to assess factors affecting TPI. Multivariate regression and receiver operating characteristic (ROC) curves were employed for analysis. Results: Complete TPI was achieved in 89.4% of foals. The ROC TPI values were conductivity ≤5 mS/cm (AUC = 0.68), Brix ≥23.4% (AUC = 0.70), and pH ≤6.4 units (AUC = 0.73). The odds ratio for TPI in 24 h post-partum was 6.1 (2.1-17.1, 95% CI) for conductivity, 3.2 (1.2-9.3, 95% CI) for pH, and 4.5 (1.5-12.7, 95% CI) for Brix index. Sensitivity and specificity of 93% (88-96 95% CI), 56% (44-7, 95% CI), 92% (87-96, 95% CI), 28% (14-47, 95% CI), 94% (88-97, 95% CI) and 18% (14-47, 95% CI) for conductivity, Brix and pH, respectively. Conclusions: Low incidence of incomplete TPI. Conclusions: Conductivity, pH and Brix are strong predictors of foals that succeed in the transfer of passive immunity; however, all three presented low to moderate specificity. The established cutoff values obtained herein can be used on-field by other foaling programs. All three handheld devices used in the study are inexpensive and ready to use on-farm.
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Publication Date: 2024-10-16 PubMed ID: 39415473DOI: 10.1111/evj.14421Google Scholar: Lookup
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  • Journal Article

Summary

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Overview

  • This study evaluated whether colostrum measurements—conductivity, pH, and Brix index—can predict the successful transfer of passive immunity (TPI) in newborn foals.
  • The researchers measured these colostrum parameters immediately after birth and correlated them with foals’ immunoglobulin G (IgG) levels 20 hours postpartum, aiming to identify reliable, easy-to-use on-farm tools to assess foal immunity transfer.

Background and Importance

  • Newborn foals rely heavily on antibodies (immunoglobulins, especially IgG) absorbed from their mother’s colostrum to gain passive immunity against infections during early life.
  • Incomplete transfer of passive immunity (TPI) can lead to higher susceptibility to diseases.
  • Colostrum quality evaluation is therefore critical; direct IgG measurement is ideal but requires laboratory equipment, which is not always practical on farms.
  • Previous studies in cattle suggest colostrum conductivity correlates with TPI, but similar associations in horses had not been definitively established.
  • Colostrum’s pH and conductivity tend to decline near and during parturition, possibly facilitating antibody absorption, but their predictive values for TPI had not been fully validated in foals.

Objectives

  • To determine if measurements of colostrum conductivity, pH, and Brix refractometer index immediately after birth can predict successful passive immunity transfer in foals.
  • To establish cutoff values for each parameter to differentiate between complete and incomplete TPI.
  • To assess the sensitivity, specificity, and predictive power of these measures for practical farm use.

Methods

  • Study Design: Field study involving 241 mares and their foals.
  • Colostrum Assessments: Conductivity, pH, and Brix index were measured immediately postpartum using handheld devices suitable for on-farm use.
  • Foal Assessments: At 20 hours after birth, blood samples collected to assess plasma IgG concentration (the key indicator of passive immunity transfer) and complete blood cell count.
  • Grouping: Foals were classified based on IgG levels—complete TPI (≥8 g/L IgG) and incomplete TPI (<8 g/L IgG).
  • Statistical Analysis: Multivariate regression analysis to evaluate associations between mare, foal, and colostrum variables and TPI outcomes.
  • Receiver Operating Characteristic (ROC) curves used to determine cutoff values maximizing predictive accuracy for TPI for each colostrum measure.

Results

  • 89.4% of foals achieved complete transfer of passive immunity.
  • Cutoff values identified with their Area Under the Curve (AUC) for predicting TPI were:
    • Conductivity ≤5 mS/cm (AUC = 0.68)
    • Brix index ≥23.4% (AUC = 0.70)
    • pH ≤6.4 units (AUC = 0.73)
  • Odds Ratios (with 95% confidence intervals) indicating increased likelihood of complete TPI when colostrum parameters met cutoff values:
    • Conductivity: 6.1 (2.1-17.1)
    • pH: 3.2 (1.2-9.3)
    • Brix index: 4.5 (1.5-12.7)
  • Sensitivity and specificity values:
    • Conductivity: Sensitivity 93%, Specificity 56%
    • Brix index: Sensitivity 92%, Specificity 28%
    • pH: Sensitivity 94%, Specificity 18%

    (Values in parentheses represent 95% confidence intervals)

Conclusions and Implications

  • Colostrum conductivity, pH, and Brix index are strong predictors of which foals will successfully acquire passive immunity.
  • All three parameters showed high sensitivity but relatively low to moderate specificity; they are effective at identifying foals likely to have complete TPI but less effective at ruling out incomplete TPI.
  • The proposed cutoff values can be applied in practical farm settings using handheld, inexpensive devices, facilitating early identification of foals at risk and timely intervention.
  • These evaluation tools provide quick, on-field assessments that can aid foaling programs in managing neonatal foal health and reducing morbidity associated with inadequate passive immunity transfer.

Additional Considerations

  • The low incidence of incomplete TPI noted (about 10.6%) suggests generally good colostrum management or mare health in the studied population.
  • Further research may be needed to improve specificity or combine these tests with other markers to enhance diagnostic precision.
  • Handheld devices’ ease of use and affordability make them well suited for widespread on-farm adoption.

Cite This Article

APA
Magalhaes HB, Canisso IF. (2024). Colostrum conductivity, pH and Brix index as predictors of passive immunity transfer in foals. Equine Vet J, 57(4), 898-903. https://doi.org/10.1111/evj.14421

Publication

Equine veterinary journal
ISSN: 2042-3306
NlmUniqueID: 0173320
Country: United States
Language: English
Volume: 57
Issue: 4
Pages: 898-903

Researcher Affiliations

Magalhaes, Humberto Borges
  • Department of Veterinary Medicine, University of Illinois Urbana-Champaign, Urbana, Illinois, USA.
Canisso, Igor Frederico
  • Department of Veterinary Medicine, University of Illinois Urbana-Champaign, Urbana, Illinois, USA.

MeSH Terms

  • Animals
  • Colostrum / chemistry
  • Colostrum / immunology
  • Colostrum / physiology
  • Horses / immunology
  • Female
  • Hydrogen-Ion Concentration
  • Immunity, Maternally-Acquired
  • Animals, Newborn / immunology
  • Pregnancy
  • Electric Conductivity
  • Male

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Citations

This article has been cited 1 times.
  1. Capone A, Merlo B, Begni F, Iacono E. Equine Colostrum-Derived Mesenchymal Stromal Cells: A Potential Resource for Veterinary Regenerative Medicine. Vet Sci 2025 Jul 19;12(7).
    doi: 10.3390/vetsci12070681pubmed: 40711341google scholar: lookup
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