CONTINUOUS VERSUS SINGLE DRAINAGE OF MILK FROM THE BOVINE MAMMARY-GLAND DURING A 24-HOUR PERIOD

Five primiparous and five multiparous cows were used to determine if m ammary cisternal storage of milk during a 24 h period of milk accumula tion limited milk secretion. In addition, we investigated if there is a parity effect for the capacity of the mammary cisternal compartment to hold a 24 h accumulation of milk secretion, and studied the movemen t of milk from the alveolar compartment into the cisternal compartment . All cows were fitted with catheters in all teats in order to collect cisternal and alveolar milk fractions separately. For a 24 h period o f milk accumulation, the milk was drained once (after 24 h) from one s ide of the udder (OD), and continuously from the other side of the udd er (CD). There was no significant parity effect for cisternal, alveola r and total milk volumes at 24 h. Therefore, data from primi- and mult iparous cows were pooled for subsequent analyses. Cisternal milk volum e from CD glands was higher than that from OD glands (P < 0.01), indic ating that cisternal storage of milk in the mammary gland may be limit ing to milk secretion during 24 h milking intervals. Alveolar volumes did not differ between OD and CD, but, as a result of the higher ciste rnal milk volume, total milk volume was highest in the CD glands (P = 0.05). Movement of milk from the alveolar into the cisternal compartme nt was intermittent. Moreover, analyses of the slopes of individual mi lk accumulation profiles of the first 6 h of accumulation revealed tha t the cisternal compartment starts filling immediately following milki ng, although the rate of filling is relatively low until 7-8 h postmil king.