Machine milking–induced changes in teat canal dimensions as assessed by ultrasonography

摘要

Changes in teat canal diameter as induced by machinemilking are thought to be related to teat canal penetrabilityand susceptibility to new intramammary infections.The objective of this study was to describe theeffects of machine milking on teat canal dimensions asassessed by ultrasonography and to evaluate postmilkingchanges of teat canal dimensions throughout an 8-hmilking interval. Ultrasonographic images were takenof the left front and right hind teats of 80 Holstein cowsmilked 3 times per day. Imaging occurred before attachmentof the milking unit after completion of premilkingudder preparation (t−1), immediately after removal ofthe milking unit (t0), and then every hour after milkinguntil 8 h had elapsed (t1 to t8). Teat canal lengthand teat canal diameter (at the proximal, middle, anddistal regions) were measured. General linear mixedmodel analysis indicated differences in the relativechange of teat canal length (compared with t−1) withleast squares means (LSM) and 95% confidence interval(95% CI) of 11.1% (8.7–13.4%) after machine milking(t0). Teat canal length decreased throughout the 8-hmilking interval but remained elevated relative to t−1.Teat canal diameter at the proximal and middle regionsincreased near the end of the milking interval, whereasthat at the distal region did not change meaningfullyduring the 8 h of observation. Our findings suggest thatthe teat canal and its surrounding tissue is in a stateof near-constant remodeling in cows milked 3 timesdaily. Future work is warranted to study the associationbetween ultrasonographically assessed changes of teatcanal dimensions after machine milking and teat canalpenetrability to mastitis-causing pathogens.