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
Rj. Holdaway et al., 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, Australian Journal of Dairy Technology, 51(2), 1996, pp. 64-71
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.