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Abstract
Six hundred and ninety five lactating cows (2780 quarters) from a total 2300 Holstein Friesian dairy cows at Fayoum district, Egypt were examined for the prevalence of subclinical mastitis and its associated risk factors during the period of December 2016 to November 2017. Four hundred forty four lactating cows with 1145 quarters were positively for SCM with prevalence of 63.88 and 41.18% at cow and quarter level respectively based on California Mastitis Test, Electrical Conductivity with a mean value (6.27 ± 0.066 mS/cm) and Somatic Cell Count with mean value 8.8{u00D7}105 ± 9.2{u00D7}103 cells/ml.The risk factors investigated in this study revealed that the highest percentage of SCM was observed in the winter; late stage of lactation and in cows of 4-5 years old. Also the occurrence of SCM was higher in cows with 2nd, 3rd and 1st parity number than those with 4, 5, 6th parity number respectively.The statistical analytical results also revealed that there is highly significance (p = 0.028) between parity and other studied risk factors. The results of chemical analysis of the milk samples along the four seasons of the year which done by the Lactoscan milk analyzer revealed that; the statistical analysis results indicated that there is a significant difference (P < 0.05) in fat % and SCC between winter and autumn, moreover, there is a significant difference (P < 0.05) between (winter and autumn) and (winter and spring) in the parameters of protein, SNF and lactose content. So, milk composition especially contents of fat, protein and lactose were found to be lower with a significant increase in Salt % and SCC of SCM milk samples