The relationship between the occurrence of subclinical mastitis and milk quality in medium-sized Holstein cow farms in Albania.

Abstract

Subclinical mastitis (SCM) reduces both milk production and milk quality. In this study, the prevalence of SCM, as determined by the California Mastitis Test (CMT), was analyzed in relation to lactation year, milk density, lactose content, electrical conductivity, and fat content at both the individual cow level and the farm level. The focus was on the overall prevalence of CMT-positive cases within the farms and the mean values of physicochemical changes in milk for each farm. A total of 711 udder quarters from 178 Holstein cows across nine dairy farms were sampled at three intervals during lactation (i.e., in three lactation periods). The number of cows per farm ranged from 21 to 140, covering various lactation stages. A CMT score of 1+ in any quarter was considered SCM-positive. The significance and correlation of SCM's impact on changes in physicochemical milk parameters were analyzed using a robust compound regression. Prevalence of SCM was found to be between 0.14 and 0.63. High prevalence of SCM showed a significant increase in milk conductivity and a significant decrease in milk lactose, protein, solid non-fat (SNF) content, and density. The prevalence of mild and severe SCM varied across different seasons and lactation stages (p<0.05). Significant correlations (p<0.05) between lactation year, lactose content, electrical conductivity, SNF content, and protein were measured at the farm level using a milk analyzer and compared with SCM (R^2=0.28; R^2=0.41; R^2=0.26; R^2=0.36; R^2=0.39). These findings suggest that physicochemical milk parameters, which are routinely measured in Albanian dairies, can serve as an effective early-warning indicator for dairy farms to detect potential cases of SCM.