Bacterial subclinical mastitis and its effect on milk quality traits in low-input dairy goat herds

The objective of the study was to investigate and quantify the effects of subclinical mastitis (SCM) on the gross chemical composition of milk in low-input dairy goat herds. Dairy goats (n=590) of two native Greek breeds from four representative low-input farms were randomly selected and used in the study. Α prospective study was conducted, including monthly monitoring and milk sampling of the same individual goats during the course of two consecutive milking periods. Mixed linear regression models were built to assess how the chemical composition of milk was affected by (1) SCM and (2) the different pathogens isolated from SCM cases. Goats with SCM had lower milk-fat content (MFC), daily milk-fat yield (DMFY), milk-lactose content (MLC) and daily milk-lactose yield (DMLY), and slightly higher milk-protein content (MPC) and daily milk-protein yield (DMPY), compared with goats without SCM. Milk produced by goats with SCM due to coagulase-positive staphylococci and Mycoplasma agalactiae had significantly lower MFC, DMFY, MLC and DMLY, and higher MPC and DMPY, compared with the milk produced by healthy goats. Finally, goats with SCM due to coagulase-negative staphylococci had lower DMFY, MLC and DMLY and higher DMPY compared with the healthy ones.