Ultrasonographic changes of dairy cow teat canals during the dry period

The aim of this study is to determine whether the formation of the teat canal keratin plug could be evaluated by ultrasonography in dairy cows. First, ultrasound examinations were conducted on the teats of 4 dry multiparous Holstein cows (20 teats). The hyperechoic lines observed on the ultrasound of the teat canals were assessed using a 4-point scale. The teat canal score (TCS) was defined as follows: one hyperechoic line in the teat canal as TCS1, the 2 lines as TCS2, the unclear lines as TCS3, and no lines as TCS4. On Day 0 and Day 1 of the dry period, 100 % and 87.5 % of the teats were TCS1, respectively. From Day 5 onwards, over 80 % of the teats were classified as TCS2, with no TCS1s. The proportion of teats classified as TCS3 or TCS4 ranged from 6.3 % to 18.8 % throughout the study period. Second, ultrasound examinations of teat canals from slaughtered dairy cows were conducted, and the wet weight of the keratin plugs were measured. The distribution of TCS was 37.5 % for TCS1, 62.5 % for TCS2, and 0 % for TCS3 and TCS4. The wet weight of keratin plugs in TCS2 (12.4 ± 6.5 mg) was significantly greater than in TCS1 (6.5 ± 3.0 mg). These findings indicate that keratin plug formation in the teat canal can effectively be evaluated using ultrasonography. Moreover, the teat canal scoring system introduced in this study offers a viable method for assessing keratin plug formation during the dry period and may be applicable in mastitis risk assessment.