Mare colostrum quality and relationship with foal serum immunoglobulin G concentrations and average daily weight gains.
Authors: Gallacher Kirsty, Champion Katherine, Denholm Katharine S
Journal: Equine veterinary journal
Summary
# Editorial Summary Passive immunity transfer failure remains a significant clinical concern in foal medicine, with roughly one in five foals in this cohort of 535 Thoroughbreds presenting with partial or total failure of immunoglobulin transfer (serum IgG ≤8 g/L). Gallacher and colleagues conducted a retrospective analysis examining the relationship between mare colostrum quality (measured by Brix refractometry), foal serum IgG concentrations, and subsequent growth, finding that colostrum Brix percentage emerged as a strong predictor of foal immune status—each 1% increase in Brix correlated with a 0.25 g/L rise in foal serum IgG (p<0.001), alongside smaller but significant contributions from birthweight and foaling year. The analysis also revealed important temporal patterns: foals born later in the season demonstrated both lower colostrum quality and reduced growth rates, whilst older mares produced colostrum with significantly lower Brix values, suggesting age-related changes in immunological output warrant closer monitoring at breeding. These findings support routine pre-suckle colostrum assessment in at-risk populations and highlight the need for targeted intervention strategies when Brix levels fall below the 20% threshold (observed in 21% of samples), whilst also pointing practitioners towards seasonal and mare-age factors that should inform periparturient management and foal IgG screening protocols.
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Practical Takeaways
- •Monitor colostrum quality using Brix refractometry at foaling—aim for ≥20% Brix; approximately 1 in 5 mares produce substandard colostrum
- •Older mares are at higher risk of producing lower-quality colostrum, so prioritize passive transfer assessment in foals from aged dams
- •Foals born later in the season (increasing calendar month) show reduced growth rates and lower colostrum IgG transfer, requiring closer monitoring during summer/autumn foalings
Key Findings
- •20.9% of colostrum samples measured <20% Brix, indicating poor quality colostrum in approximately 1 in 5 mares
- •20.4% of foals had serum IgG ≤8 g/L (PFTPI or TFTPI), with 2.2% having TFTPI (<4 g/L)
- •Each 1% increase in mare colostrum Brix was associated with a 0.25 g/L increase in foal serum IgG (p<0.001)
- •Increasing dam age at foaling was significantly associated with lower colostrum Brix percentages
- •Month of birth significantly affected both colostrum quality and foal average daily gains, with declining values in later calendar months