Using records from the Milk Registration Organization for 254 dairy-goat farms located in western France, the economical impact of mammary gland inflammation on milk yield and composition was measured after 200 days of lactation. This assessment was performed in groups of goats belonging to the same farm and the same breed and having the same parity. Three levels of somatic cell count (SCC) were defined in order to discriminate goats on the basis of the intensity of inflammatory reaction of their udder: < 750,000 cells/mL (CCI1), between 750,000 and 1,750,000 cells/mL (CCI2), > 1,750,000 cells/mL (CCI3). From 404 groups characterized by an average number of 12,4 CCI1 goats and 14,2 (CCI2 + CCI3) goats, the average milk yield of the goats whose SCC was superior to 750,000 cells/mL was inferior to that of the CCI1 goats in 79.2% of the groups. In a sub-sample of 366 groups, the average loss of milk production for the CCI2 goats compared to the CCI1 ones was 55 kg. In an other sub-sample of 41 groups, the milk production average loss of the CCI3 goats reached 132 kg. For all of the 404 groups, (CCI2 + CCI3) goats had a lower fat content of 0.3 g/kg and in contrast a higher protein content of 0.6 g/kg. A second evaluation using a multidimensional variance analysis model in a population of 20796 goats showed the same results.