Effects of Vacuum Level and Milking Duration on Guernseys and Holsteins Differing with Respect to Lactation Number and Status of Udder Health. I. Udder Health

The effects of vacuum level and machine milking duration on udder health are controversial Although observations from field studies suggest that both of these factors might be detrimental to udder health, data from controlled experimentation have failed to relate vacuum level and udder health With regard to machine milking duration, Dodd et al. (4) reported a greater incidence of clinical and subclinical mastitis in first-calf heifers subjected for their entire lactation to an 8-minute duration than in heifers subjected to a 4-minute 'duration. In possible contrast, half-udders of first-calf mastitis-free heifers subjected for a 40-week experimental period to either a "normal" or "twice normal" milking duration did not have significantly different inci(tellces of clinical mastitis, occurrences of mastitis organisms, or histological changes Similar findings were reported (10) for cows more advanced in the number of lactations and whose whole udders were milked for "normal," "twice normal," or "four normal" durations for 6 weeks. Log of leucocyte count and chloride content, however, were affected by milking duration in the latter two studies (9, 10). In the first-calf mastitis-free heifers, normal duration halves of udders had a greater log leucocyte number and chloride concentration than twice normal halves, whereas in the second study a direct relationship of log leucocyte count and chloride content with the log of milking duration was observed. The results from halves of udders were unexpected and difficult to evaluate ; however, those from whole udders were interpreted as irritation directly attributable to increased milking duration.