The teat canal is important in the defense against invading pathogens, but its functional features can be impeded by the milking process. The objective of our study was to compare teat morphology before and after a standard milking procedure using high-resolution ultrasonography. Tissue changes were determined by measuring inner traits of teat morphology: teat width, teat end width, teat cistern width, diameter of the lower and upper teat wall, teat canal length, and teat canal diameter. Additionally, 3 traits describing the distal teat canal and its external orifice were established: diameter of the distal teat canal orifice, distal teat canal perimeter, and distal teat canal surface. In the first trial, we verified the repeatability of scanning over time with a mixed model. During the second trial, significant changes after milking were observed for all measured traits of teat morphology except teat end width. The traits from the distal teat canal and its orifice were remarkably changed by milking: distal teat canal orifice, +28.9%; distal teat canal perimeter, +25.0%; and distal teat canal surface, +41.5%. Comparing multiparous versus primiparous cows, higher values of teat width, teat end width, and teat canal length were observed in the older animals. Testing the effect of milk yield on teat dimensions, cows with milk yields >11.0 kg/afternoon milking were found to have larger teat widths, teat end widths, and cistern widths before attachment of the cluster. Furthermore, we observed associations of inner teat morphology toward bacterial counts in the appropriate milk. Regarding this udder health-related parameter especially, the newly established traits showed a connection. Teats in which milk showed bacterial growth had larger distal teat canal perimeters and distal teat canal surfaces. High-resolution ultrasonographic scanning of dairy teats allowed a detailed visualization of the inner morphology. The applied procedure can therefore serve as a useful tool for comparison and evaluation of different milking techniques by analyzing the resulting changes of the morphological traits. The thorough description of teat tissue can also be applied for drawing conclusions on the status of the teat canal's physical and mechanical defense function.
