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In 90 Sarda dairy ewes the effects of lactation stage, parity, &beta;-lactoglobulin genotypes, and somatic cell count (SCC) on<br />the milk content of total protein (TP), casein (CN), whey protein (WP) and its fractions &alpha;-lactalbumin (ALA), &beta;-lactoglobulin<br />(BLG), serum albumin (SA), immunoglobulin (IG) and lactoferrin (LF) were analysed using a linear mixed model.<br />Mean values of variables (g/l) were: TP (54.0), CN (43.0), WP (11.0), BLG (4.78), ALA (1.37), SA (0.61), IG (3.83) and<br />LF (0.28). The lactation stage significantly affected all the variables analysed. TP, CN and WP concentrations tended to<br />increase throughout lactation, with the increase of WP being more pronounced than the corresponding variation in CN.<br />There was no definite trend in BLG content, whereas ALA concentration decreased as lactation progressed. The parity<br />affected almost all variables studied. WP concentration differed significantly only between the second and fourth parity<br />(10.45 vs 11.44 g/l). BLG and SA concentrations were significantly lower in the youngest ewes. The BLG genotype affected<br />milk yield, but no effects were observed on the components of the milk. The SCC influenced almost all variables studied.<br />The TP concentration was significantly higher in milk with SCC >1,000,000 (55.0 g/l) than in milk with lower SCC<br />(53.4 g/l). This was mainly due to the increase of WP (12.52 and 10.24 g/l in milk with SCC above and below<br />1,000,000/ml respectively), especially in those WP fractions originating from blood.