Effects of Milking Interval on Selected Milk Constituents from Normal and Infected Quarters

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Abstract
Effects of milking interval on electrical conductivity, Cl-, Na, K, 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. The effect of milking interval was significant on all variables measured. Conductivity, Cl-, Na and cell counts were highest at the 3 h interval, lowest at the 9 h interval and then steadily increased from 9 to 15 h. Lactose followed the opposite trend and was highest at the 9 h interval. Trends were similar in samples from uninfected and infected quarters; however, changes were more pronounced in the latter. Conductivity changes due to 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 would be more sensitive for detecting masitits than measurements on foremilk or primary milk, especially when measured after short milking intervals.