RENNETING PROPERTIES OF MILK FROM INDIVIDUAL EWES - INFLUENCE OF GENETIC AND NONGENETIC VARIABLES, AND RELATIONSHIP WITH PHYSICOCHEMICAL CHARACTERISTICS

The physicochemical characteristics and the renneting properties of mi lks from Lacaune ewes are reported. The ewes belonged to divergent gen etic lines termed 'low' or 'high' and were selected on a combination o f fat and protein yield. The 179 second to fifth parity ewes were samp led three times during lactation at about 50, 135 and 175 d in milk. P hysicochemical and renneting variables were principally influenced by days in milli and somatic cell count, whereas beta-lactoglobulin genot ype, parity and divergent lines had relatively few effects. Fat and pr otein content increased throughout lactation, whereas rennet gel firmi ng rate decreased. Salt distribution and micellar characteristics were also significantly affected by days in milli. Milks with high somatic cell count mere characterized by high values of pH and soluble nitrog en content and rennet coagulation properties were significantly affect ed at > 3 x 10(5)-5 x 10(5) cells/ml milk. Divergent lines had a stron g effect on milk yield, but no effect on milk composition consistent w ith the selection criteria. Gel firming rate was slightly higher in mi lks from high;yield ewes. Protein content, Ca concentration, pH and mi celle characteristics were the main factors related to variations in t he renneting properties of the milks.