Investigations on teat canal length in teats with milk flow disturbances

The objective of this study was to evaluate teat canal length as a test for tissue ruptures in the area of the teat canal in teats with milk flow disturbances (Medl's test). A total of 133 dairy cows affected with milk flow disturbances in one teat were used for this study. The teat canal length of the affected teat was compared with the teat canal length of the contralateral teat of the same cow. Milk flow disturbances were diagnosed by endoscopy. Diagnoses were categorized as tissue ruptures in the area of the teat canal or other causes such as narrowing of the teat canal, or free foreign bodies in the teat cistern. The median teat canal length was 11 mm in teats with milk flow disturbances, and 8 mm in contralateral control teats. When the test criterion was lengthening of the teat canal by > or =2 mm, 79% of the teat canals with tissue ruptures tested positive (true positive), but 47% of teat canals without tissue ruptures also tested positive (false positive). When the test criterion was unchanged teat canal length, 47% of teat canals with tissue ruptures tested positive, and only 7% of teat canals without tissue ruptures tested positive. Thus, it is concluded that Medl's test may be useful in differentiating causes of milk flow disturbances. However, a more accurate diagnosis may be made by teat endoscopy.