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 dist urbances (Medl's test). A total of 133 dairy cows affected. with milk flow disturbances in one teat were used for this study. The teal canal length of the affected teat was compared with the teat canal length of the contralat eral teat of the same cow. Milk flow disturbances were diagnosed by endosco py. Diagnoses were categorized as tissue ruptures in the area of the teat c anal or other causes such as narrowing of the teat canal, or free foreign b odies 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 greater than or equ al to 2 mm, 79% of the teat canals with tissue ruptures tested positive (tr ue positive), but 47% of teal canals without tissue ruptures also tested po sitive (false positive). When the test criterion was unchanged teat canal l ength, 47% of teat canals with tissue ruptures tested positive, and only 7% of teal canals without tissue ruptures tested positive. Thus, it is conclu ded that Medl's test may be useful in differentiating causes of milk flow d isturbances. However, a more accurate diagnosis may be made by teat endosco py.