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

Summary Twelve mastitis-free first calf heifers, nine Holsteins and three Jerseys, after a 4-week standardizing period, were randomly assigned to be milked for 40 weeks at a vacuum level of 10, 13, or 17 in. of mercury. Halves of udders were assigned to a milking duration of either normal or twice normal. Yields of total pounds of milk, PCM, and fat, and per cent 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 amount of strippings expressed as percentage of total yield tended to be less for the 13 in. 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 amounts of milk and significantly more PCM, whereas pounds of fat and per cent of fat were unaffected. The halves milked for the longer duration had significantly slower rates of decrease for total milk yield, pounds of fat, and FCM. Although no differences in the milking time, time to reach peak flow, and amount of strippings were observed, significantly less time was spent stripping, and faster average rates of flow were noted, for the halves milked for twice the normal time.