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

Mastitis is an emerging health concern in lactating mares, particularly given the growing commercial interest in mare's milk. This study evaluated the diagnostic potential of acute phase proteins (APPs), specifically serum amyloid A (SAA), milk amyloid A (MAA), and haptoglobin (Hp), measured in blood and milk as indicators of clinical and subclinical mastitis. Twenty-four Thoroughbred mares were prospectively monitored during lactation and weaning. Plasma and milk samples were collected and analyzed using commercial ELISA kits. Plasma SAA concentrations were significantly higher in mares with clinical mastitis compared to healthy (p < 0.001) and subclinically affected mares (p < 0.01), particularly on day 1 postpartum. In contrast, plasma SAA concentrations remained low 181-183 days after foaling, even in mares with subclinical mastitis. Milk MAA and Hp concentrations were significantly elevated in mares with clinical (p < 0.001) and subclinical mastitis (p < 0.05) compared to healthy mares. MAA concentrations were higher in subclinical mastitis detected during weaning (SM II group) than postpartum (SM I group) (p < 0.05). A moderate positive correlation between MAA and plasma Hp concentrations was observed in clinical mastitis cases (r = 0.57, p < 0.01), suggesting concurrent systemic and local responses, while weak correlations were found in subclinical and healthy mares. These findings suggest that plasma SAA is a useful marker of systemic inflammation in clinical mastitis, whereas MAA and milk Hp are more sensitive markers of local mammary gland inflammation, particularly in subclinical cases. Further research with larger populations is warranted to define diagnostic thresholds and explore APP dynamics throughout lactation.