A Further Study of Effects of Vacuum Level and Milking Duration on Udder Health and Milk Production

Poor machine milking practices, especially high vacuum and excessive milking duration, have long been associated with an increased incidence of mastitis (1,6).Dodd et al. (3) found a higher incidence of clinical mastitis in first-calf heifers milked for an 8-minute duration than in those milked for 4 minutes.Previous work from this station (7) reported no significant differences in leucocyte, chloride, and pH values of milk from mastitis-free first-calf heifers milked at vacuum levels of 10, 13, or 17 in. of mercury.The secretion from udder halves milked for a normal duration had significantly greater leucocyte and chloride values and a greater linear rate of increase during the lactation period for leucocyte, chloride, and pH values than did halves milked for a twice normal duration.No significant differences in freedom from mastitis organisms, teat erosions, or udder fibrosis were observed among the vacuum levels or between the milking durations.This study was undertaken to further evaluate effects of vacuum level and prolonged milking on udder health and milk production.A longer milking period than those used previously was included, and the entire udder was used for each treatment in an attempt to clarify the effects of milking duration.EXPERIMEN TAL Animals and treatments.In September 1952 six Holstein and six Guernsey cows were selected from 18 animals for having leucocyte counts equal to or less than one million per milliliter in three of four pooled milk samples taken in a 2-week standardizing period, and for being free from mastitis organism in three of these four samples.None of the 12 cows used in the comparison shed mastitic organisms in any of these samples, and the (geometric) mean leucocyte count for all cows was 446,000 per milliliter during this 2-week period.These 12 cows averaged 2.4 ___ 1.4 lactations and had been in milk 175 ± 63 days at the beginning of the standardizing period.In the standardizing period all cows were milked at 13.5 in.vacuum, and the machines were removed at the operators discretion.Immediately after the standardizing period, the six cows within each breed