Factors affecting milk somatic cell count of cows with clinical mastitis

Mastitis is one of the most important diseases that results in devastating economic effect on dairy herds. Milk somatic cell count (SCC) is an udder health parameter. This study conducted to investigate the factor affecting milk somatic cell count of cows with and without clinical mastitis in previous lactations. Multiparous Holstein cows from a farm in Shiraz, southern Iran were used. The study was carried out in July and December 2010 and May 2011. Milk samples (n = 222; 20 mL) were taken from all quarters of lactating cows after the first three squirts of milk from each quarter were discarded. Milk SCC was measured using an electronic cell counting method (Fossomatic, Foss Electric, and Denmark). SPSS software (Mann-Whitney test; Spearman's rank correlation and Univariate of General Linear Model) was used for the analyses of factors affecting the milk SCC including lactation number, postpartum period or days in milk, month of sampling, milk yield, and clinical mastitis in previous lactation. Cows with mastitis in previous lactation had a greater mean milk yield and SCC compared to that of cow without mastitis. There was significant correlation between SCC and days in milk of cow without mastitis (r=0.4; p<0.05), and lactation number of cow with mastitis (r=0.2; p=0.05). Results of the present study showed that milk yield and days in milk were considerable factors for interpreting of SCC in cows without the historical information of clinical mastitis detection in previous lactation. While in cows with the clinical mastitis in previous lactation, in addition to milk yield, lactation number and month of sampling are more significant. It could be concluded that the history of clinical mastitis could be important for interpreting SCC, used as a tool to select mastitis resistance in dairy cow.