Concentrations of serum amyloid A and haptoglobin in mare blood and milk as indicators of subclinical mastitis.

Overview

• This study investigates the use of specific proteins in blood and milk—serum amyloid A (SAA), milk amyloid A (MAA), and haptoglobin (Hp)—to diagnose clinical and subclinical mastitis in lactating Thoroughbred mares.
• It identifies the potential of these proteins as biomarkers to differentiate between healthy, clinically, and subclinically affected mares, aiming to improve detection and management of mastitis in mares used for milk production.

Background

• Mastitis: An inflammation of the mammary gland, mastitis can impact milk quality and animal health and is a developing concern in lactating mares, especially due to the increasing commercial use of mare’s milk.
• Subclinical Mastitis: A form of mastitis without obvious clinical symptoms, making it hard to detect but still affecting milk production and quality.
• Acute Phase Proteins (APPs): Proteins that increase in concentration during inflammation. In mares, key APPs include serum amyloid A and haptoglobin.

Objectives

• To evaluate the levels of serum amyloid A (SAA) in plasma and milk amyloid A (MAA) and haptoglobin (Hp) in milk as indicators of clinical and subclinical mastitis in mares.
• To assess the diagnostic utility of these proteins in differentiating healthy mares from those with clinical or subclinical mastitis.
• To explore correlations between systemic and local inflammatory responses.

Methodology

• Subjects: Twenty-four Thoroughbred mares were monitored prospectively through lactation and the weaning period.
• Sample Collection: Blood plasma and milk samples were collected at different time points—particularly day 1 postpartum and 181-183 days after foaling (weaning).
• Testing: Concentrations of SAA, MAA, and Hp were measured using commercial ELISA kits, a sensitive laboratory technique for detecting specific proteins.
• Grouping: Mares were categorized into healthy, clinically mastitic, and subclinical mastitic groups. Subclinical cases were further split based on timing—postpartum (SM I) and during weaning (SM II).

Findings

• Plasma SAA:
  • Significantly higher in mares with clinical mastitis compared to both healthy and subclinical mares, especially on day 1 postpartum.
  • Remained low in all mares at 181-183 days after foaling, even those with subclinical mastitis, suggesting plasma SAA is a marker of active systemic inflammation.
• Milk MAA and Hp:
  • Elevated in clinical mastitis cases (highly significant) and subclinical mastitis (moderately significant) compared to healthy mares.
  • MAA concentrations were higher in the SM II group (subclinical mastitis during weaning) than in the SM I group (postpartum), indicating that markers in milk are sensitive to local inflammation even when systemic markers are low.
• Correlation Analysis:
  • A moderate positive correlation was found between milk MAA and plasma Hp in clinical mastitis cases, suggesting simultaneous local and systemic inflammatory responses.
  • Correlations were weaker in subclinical and healthy mares, indicating less systemic inflammatory involvement.

Interpretation

• Plasma SAA: A reliable marker for detecting systemic inflammation largely seen in clinical mastitis cases, but less sensitive for subclinical conditions.
• Milk-based markers (MAA and Hp):
  • More sensitive indicators of local mammary gland inflammation, particularly useful for identifying subclinical mastitis.
  • Can detect inflammation during later lactation stages like weaning, when systemic markers are low.
• This pattern supports the use of combined testing of systemic and local markers to improve detection and management of mastitis in mares.

Conclusions and Recommendations

• Plasma SAA is effective for identifying clinical mastitis, indicating systemic inflammation.
• Milk MAA and Hp provide valuable diagnostic information for subclinical mastitis and local mammary inflammation.
• Further studies with larger mare populations are recommended to establish definitive diagnostic thresholds for these biomarkers.
• Research should also investigate the dynamic changes of these acute phase proteins throughout the entire lactation period to better understand their roles and improve mastitis monitoring.