Evaluation of milk haptoglobin and amyloid A in high producing dairy cattle with clinical and subclinical mastitis in Shiraz

Mastitis is one of the most common diseases in dairy cattle and results in considerable loss of animals. This study was designed to evaluate milk haptoglobin (Hp) and milk amyloid A (MAA) as an inflammatory indicator for clinical and subclinical mastitis of cattle in dairy farms in Shiraz, Iran. Forty-three subclinical mastitic cows with a positive California Mastitis Test (CMT) and no clinical signs of mastitis, 28 clinical mastitic cows, and 10 healthy cows with negative CMT were selected. After confirmation of clinical and subclinical mastitis by bacterial identification, milk samples were taken from four quarters of each cow and mixed, and one sample was taken from the pooled milk. The most dominant isolated bacterium from clinical and subclinical samples was Staphylococcus aureus (n = 25; 35.2%). The most dominant isolated bacterium from clinical (19/28) and subclinical (11/43) samples was Staphylococcus spp. Of isolated bacteria of milk in cattle with clinical mastitis, 67.8% (n = 19) was S. aureus. There was no bacterial growth in 37.1% (n = 16) of cattle with subclinical mastitis. Of isolated bacteria of milk in cattle with subclinical mastitis, 13.9% (n = 6) and 11.6% (n = 5) was S. aureus and Staphylococcus epidermidis, respectively. There were significant differences (P < 0.05) in concentrations of milk Hp, MAA, and somatic cell count between clinically healthy cattle and cows with clinical and subclinical mastitis. The concentrations of milk Hp, MAA, and somatic cell count in clinical mastitic cows were significantly higher than those in subclinical mastitic cows and control group. The optimal cutoff point was set, using the receiver operating characteristic curve analysis method, to >13.43 μg/ml for MAA, >9.71 ng/ml for milk Hp, and >14 × 10⁴ cell per millilitre for somatic cell count with corresponding 100% sensitivity and 100% specificity for MAA, 83.72% sensitivity and 100% specificity for milk Hp, and 88.37% sensitivity and 100% specificity for somatic cell count. The results of this study reveal that MAA is a sensitive factor for diagnosis of subclinical mastitis in cattle.