CHANGES IN ELECTRICAL-CONDUCTIVITY AND SOMATIC-CELL COUNT BETWEEN MILK FRACTIONS FROM QUARTERS SUBCLINICALLY INFECTED WITH PARTICULAR MASTITIS PATHOGENS
Mw. Woolford et al., CHANGES IN ELECTRICAL-CONDUCTIVITY AND SOMATIC-CELL COUNT BETWEEN MILK FRACTIONS FROM QUARTERS SUBCLINICALLY INFECTED WITH PARTICULAR MASTITIS PATHOGENS, Journal of Dairy Research, 65(2), 1998, pp. 187-198
Cows with subclinical intramammary infections were identified by milk
bacteriology. The mastitis pathogens included Staphylococcus aureus (n
= 9), Streptococcus uberis (n = 10) and coagulase-negative staphyloco
cci (n =: 10). Samples of first fore milk, main flow milk and strippin
gs milk fractions were collected from each quarter and laboratory meas
urements were made of electrical conductivity, milk fat concentration
and somatic cell count. Conductivity measurements were corrected for m
ilk fat concentration and within-cow inter-quarter conductivity ratios
calculated. Repeatability estimates of all measurements between days
were calculated. In the case of infected quarters, all conductivity va
lues decreased markedly (P < 0.05) from first fore milli to main flow
milk fractions. Conductivity differences between quarters of infected
cows were substantially lower during the main milk flow phase. For qua
rters infected with Staph. aureus an increase in conductivity was obse
rved (P < 0.05) from main flow to strippings fractions. For uninfected
quarters, conductivity declined as milk fat concentration increased w
ith successive milk fractions. Variation, both within and between milk
fractions, was greater for somatic cell count than for conductivity.
Differences in conductivity between milk fractions from individual inf
ected quarters were not accounted for by changes in fat concentration
and may result from the mixing of milk from infected and uninfected re
gions of the gland. Localized infection may produce a decrease in cond
uctivity between fore milk and mid-flow fractions while differential d
rainage from an infection site in the secretory tissue may additionall
y produce an increase in conductivity from mid-flow to strippings frac
tions. Such changes may thus provide information on the location and m
agnitude of an infection. The results clearly demonstrate the importan
ce of the milk fraction when using conductivity as a diagnostic of int
ramammary infection, the highest diagnostic sensitivity being achieved
by using first fore milk samples.