Effects of milking interval on selected milk constituents from normal and infected quarters

Effects of milking interval on electrical conductivity, chloride, sodium, potassium, lactose, and somatic cell counts of milk were determined. Quarter samples of foremilk, primary milk, and strippings were obtained from 12 cows after 3, 6, 9, 12, and 15-h milking intervals. The preceding interval to all experimental intervals was standardized at 12 h. Infection status of quarters was ascertained by bacteriological analysis. Effect of milking interval was significant on all variables measured. Highest conductivity, chloride, sodium, and cell counts were at the 3-h interval but declined to their lowest at the 9-h interval. Conductivity, chloride, and sodium then steadily increased from 9 to 15 h. Lactose followed the opposite trend and was highest at the 9-h interval. Trend was similar in samples from both uninfected and infected quarters; however, changes were more pronounced in the latter. Change of conductivity from infection varied with type of sample and milking interval with strippings being the most sensitive. All samples were least sensitive to these changes at the 9-h interval. Conductivity measurements on strippings will be more sensitive for detecting mastitis than measurements from foremilk or primary milk, especially measured following short milking intervals.