Subclinical mastitis is a very important health problem affecting dairy cattle. It is associated with reduced milk quality and quantity and if not recognized and controlled in time it increases the risk of transferring of the infection to the healthy cows. Currently, somatic cell count (SCC), California mastitis test (CMT) and bacterial culture still are the standard gold tests used for detection of subclinical mastitis.The drawbacks of these conventional techniques necessitate the search of more sensitive biomarkers with high clinical accuracy and sensitivity. The activities of leukocyte enzymes including lactate dehydrogenase (LDH) and alkaline phosphatase (ALP), which increase during mastitis, are potential biomarkers for
detection of subclinical forms of mastitis. The objective of this study was to evaluate the diagnostic potential of milk LDH and ALP for diagnosis of subclinical mastitis in dairy cows as compared to SCC, CMT and bacterial culture. A total of 108 clinically apparently healthy cows were randomly selected in this work. Using SCC, CMT and bacteriological isolation, 50
cows (47%) were considered to be affected by subclinical mastitis. The following bacterial species were recovered from thesemilk sample; Staphylococcus aureus(18%), Staphylococcus epidermidis (14%), E. coli (14%), Klebsiella spp (36%), proteus spp (18%). The collected milk samples were examined for the LDH and ALP Enzymes activities. The mean and
median activities of LDH and ALP were higher in the milk samples collected from cows with subclinical mastitis and reached to 818 B*± 38.2 and 123.4 B* ± 3.2 µ/L, respectively, as compared to 103 ± 2.5 and 30.3 A ± 1.3, respectively, in milk samples from normal cattle     
proved free from subclinical mastitis. The obtained results revealed that the LDH and ALP
activities in milk samples are reliable sensitive biomarkers for detection of bovine subclinical
mastitis