A COMPARISON OF INDIRECT METHODS FOR DIAGNOSIS OF SUBCLINICAL INTRAMAMMARY INFECTION IN LACTATING DAIRY-COWS .1. THE EFFECTS OF BACTERIAL INFECTION, STAGE OF LACTATION AND AGE OF COW ON 8 PARAMETERS IN FOREMILK FROM INDIVIDUAL QUARTERS, WITH AN INITIAL STUDY OF DIFFERENCES BETWEEN MILK FRACTIONS

Eight parameters - somatic cell count, electrical conductivity, pH, N- acetyl-beta-D-glucosaminidase (NAGase) activity, and the concentration s of sodium, potassium, lactose and alpha T-antitrypsin - were measure d in milk samples from individual quarters, in two experiments. Experi ment 1: The eight parameters were measured in strict foremilk, foremil k, midmilk and strippings from 20 individual quarters, nine of which w ere free of bacterial infection. The somatic cell count, pH, NAGase ac tivity and sodium concentration increased during the milking process; the opposite was true of the concentrations of lactose and potassium, for both infected and uninfected quarters. The differences in the conc entrations of a given parameter between infected and uninfected udder quarters were generally greater in strippings than in foremilk fractio ns, although the interaction term was not significant for six of the p arameters. Experiment 2: The eight parameters were measured in quarter foremilk samples taken from 121 cows in three herds, at monthly inter vals. Between 10% and 19% of quarters showed growth by a pathogen duri ng the period. Bacterial infection of the udder caused statistically s ignificant increases in the somatic cell count, NAGase activity, elect rical conductivity and the concentrations of sodium and alpha 1-antitr ypsin, and a statistically significant decrease in the concentration o f lactose; effects on the potassium concentration and on the pH of the milk were quantitatively smaller and differed between herds. The stag e of lactation exerted significant effects on all of the parameters; s omatic cell count, sodium concentration, electrical conductivity, pH, NAGase activity and ctl-antitrypsin concentration, increased during mi d to late lactation, while the concentrations of potassium and lactose tended to decrease, Milk from older cows exhibited increased levels o f NAGase activity, electrical conductivity and sodium ions, while the concentrations of lactose and of potassium were lower for older animal s. The effects of the age of the cow on the somatic cell count and on the alpha 1-antitrypsin concentration varied between herds.