Loss in milk yield and related composition changes resulting from clinicalmastitis in dairy cows

Relationships between clinical mastitis and milk yield and composition in d airy cows were reviewed. Requirements for inclusion were: data had to be co llected after 1975; dependent variables for milk yield and milk composition had to be defined at the cow level; mastitis cases had to be defined by cl inical signs, and at least 250 lactations had to be considered. Twenty stud ies dealing with milk-yield loss and, for four of them, also with related c omposition changes were selected. Study populations, design of data collect ion, and analysis methods differed widely between studies. As expected from these differences - but also due to structural-variation factors such as t ype of pathogen, animal and production level - estimates for milk-yield los ses differed in average magnitude and pattern. Literature data regarding ch anges in milk-fat 56 and total-protein % changes were contradictory. Critiq ues of materials and methods allowed us to propose some final recommendatio ns for values to be used as basic inputs in economic calculations of losses caused by mastitis. (C) 1998 Elsevier Science B.V. All rights reserved.