SOMATIC-CELL COUNT IN BELGIAN FRISIAN CATTLE

Somatic cell count (S.C.C.) distribution is not normal, several transf ormations of S.C.C. data are studied. Naturel logarithm of the geometr ic mean for the 1 0 first monthly control has been choosen as estimato r of lactation S.C.C. (305 d.). Evolution of S.C.C. related to stage o f lactation follows an inverted lactation curve (Kg milk). A linear mo del has been fitted to the S.C.C. for lactation 1, 2, 3, 4 and more. F ixed effects included in the model are: herd production level, herd S. C.C. level, year and month of calving and class of production of the a nimal. Most important effects are herd S.C.C. level (R2 = 1 0, 82 to 1 3,98 % for lactation 1 to 4+), year of calving (R2 = 9,39 to 1,39 % f or.lactation 1 to 4+), and class of production of the animal (R2 = 0,3 8 to 2,41 % for lactation 1 to 4+). S.C.C. increase with lactation num ber. Only the intertaction between year and month of calving has a R2 greater than 1 %.