Effects of Vacuum Level and Milking Duration on Milk Production, Milking Time and Rate of Milk Flow in Mastitis-Free First Calf Heifers

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Abstract
After a 4-wk. standardizing period, 12 mastitis-free 1st calf heifers (9 Holsteins and 3 Jerseys) were assigned to be milked for 40 wks. at a vacuum level of 10, 13, or 17 in. Hg. Halves of udders were assigned to a milking duration of either normal or twice normal. Yields of total lbs. of milk fat corrected milk (FCM), and fat, and percentage of fat were unaffected by milking at different vacuum levels. Cows milked at higher vacuums tended to be more persistent. Milking time decreased significantly with increasing vacuum and rate of flow increased, but the amt. of strippings expressed as percentage of total yield tended to be less for the 13-in. Hg group. Stripping time and time to reach peak flow did not seem to be directly related to vacuum levels. Halves milked for the twice normal time gave slightly greater amts. of milk and significantly more FCM, whereas lbs. of fat and percentage of fat were unaffected. Halves milked for longer durations had significantly slower rates of decrease for total milk yield, lbs. of fat, and FCM. Although no differences in the milking time, time to reach peakflow, and amt. of strippings were observed, less time was spent stripping, and faster avg. rates of flow were noted, for halves milked twice the normal time.