FACTORS INFLUENCING VARIATION OF TEST DAY MILK-YIELD, SOMATIC-CELL COUNT, FAT, AND PROTEIN IN DAIRY SHEEP

Between January and July 1992, 8403 monthly test day records were obta ined from 3202 ewes from 22 Churra dairy flocks in the Castilla-Leon r egion of Spain. Variables measured were milk yield, SCC, and fat and p rotein percentages; means were 912 ml, 1501 x 10(3) cells/ml, 6.76%, a nd 6.28%. Analysis of variance showed significant effects of flock, st age of lactation, parity, and type of birth on milk yield, SCC, and co mposition. Variability in SCC among flocks was high and ranged from 42 0 to 2719 x 103 Cells/ml. During lactation, SCC and fat and protein pe rcentages showed increases of 31.2, 37.6, and 20.3%. Twin birth ewes h ad higher SCC (8.6%) and yield (4.4%) than single birth ewes. However, fat and protein fell 1.7 and .8% in twin birth ewes. The parity effec t was highly significant for yield, SCC, and fat; first lactation was always lower. A statistical model similar to that for dairy cattle was used to predict milk yield on the basis of flock, ewes within the flo ck, lactation stage, parity number, type of birth, and SCC. The model predicted 73% of the variation in milk yield.