Influence of somatic cell count on ewe's milk composition with particular reference to casein fraction

Ovine milk samples, from 240 half udders, with low (<500 x 103/ml), and high SCC (>1000-2000 x 103/ml) were obtained from a flock of 120 primiparous Sarda ewes. Chemical analysis, immuno-electrophoretic and HPLC-ESI/MS techniques were carried out in order to evaluate the influence of SCC on ewe’s milk composition. Dry matter, fat, true protein, casein (CN), non protein nitrogen and urea contents were not affected by SCC level up to 2000 x 103/ml. The pH value of the milk and the whey protein content significantly increased together with the SCC while lactose content resulted lower in milk with high SCC. By electrophoresis at alkaline pH and immunoblotting with polyclonal antibodies against s1, s2, and -CN, the electrophoretic patterns of milk samples with high SCC showed a different heterogeneity at level of each casein fraction respect to ones with low SCC. In the former case, the casein heterogeneity was due to a synergic action of two phenomena: proteolysis by plasmin action on s2 and -casein, mainly, as well as alterations of phosphorylation degree, close related to an increased alkaline phosphatase activity, with a concomitant loss of phosphate groups.