Cumulative Effect of Subclinical Mastitis on Immunological and Biochemical Parameters in Cow Milk

Mastitis is a complex and multifactorial disease that leads to chemical, physical, and bacteriological changes in milk, which is associated with great economic losses. This study was carried out on lactating cows to investigate the effect of subclinical mastitis (SCM) on milk production through the estimation of immunological and biochemical characteristics of milk. Therefore, a total of 200 apparently-healthy lactating cows were randomly selected from different areas in Baghdad and Maysan provinces in Iraq from April to July 2021, and 100 ml of fresh milk was directly collected from each cow. Milk samples were examined by the California mastitis test (CMT), and IgG concentration in milk was estimated by the ELISA method. Moreover, the changes in biochemical parameters and enzymatic parameters were analyzed to determine the prevalence of SCM. Based on the results of the CMT test, the prevalence of SCM was 41.5% with a significant increase in a mild degree of severity (61.45%). IgG antibodies increased significantly in positive cows (4.92± 0.21 µg/ml). Significant prevalence of infection was observed among cows ≥5 years old compared to those <5 years, crossbred ones compared to natives, and those with lower milk production without udder/milk abnormalities, compared to cows with normal milk production. However, a significant difference was observed between the two regions under investigation (i.e., Baghdad and Maysan provinces of Iraq). Results of biochemical and enzymatic parameters showed significant increases in the concentration of Cl, FFA, and Na, and a reduction in LAC and TP, though not in Ca and K. The pH of mastitis milk was significantly higher. Although no significant difference was observed in the values of ALT and LDH, AST was increased in mastitis milk. In conclusion, this study is one of the first reports on the estimated concentration of IgG in mastitis milk samples in Iraq. Increases in the concentration of SSCs and IgG in milk can apply to the detection of intra-mammary infections.