Incidence of udder cleft dermatitis (UCD) in dairy cows and risk factors for transitions to UCD

Udder cleft dermatitis (UCD) is a common skin condition in Swedish dairy cows, affecting the anterior parts of the udder. The main objective of this study was to investigate incidence rate and duration of UCD in a 1-yr longitudinal study. Other objectives were to investigate risk factors for transitions from being healthy to having mild or severe UCD, and from having mild UCD to having severe UCD, and associations between UCD and clinical mastitis, somatic cell count (SCC) and hock lesions. Seven herds were included in the study and visited 9 times each at 6-wk intervals. At the visits, mild and severe UCD lesions, hock lesions, udder conformation traits, and hygiene scores were registered for each cow milked in the milking parlor. Information on breed, parity, days in milk (DIM), results from test milkings (milk production, SCC, and urea level), and veterinary treatments was also obtained. A UCD case was defined as one or several consecutive observations of UCD. The incidence and duration of UCD were described. Mixed-effect logistic regression models were used to analyze associations between potential risk factors and transitions to any type of UCD. Separate risk factor analyses were performed for transitions to mild and severe UCD. Associations with SCC, mastitis, and hock lesions were also analyzed with mixed-effect logistic regression models. The mean overall incidence of new UCD cases for all visits and herds was 0.5 cases per cow-year at risk. Risk factors associated with a higher risk of a transition to any type of UCD and mild UCD were breed (Swedish Red vs. Swedish Holstein), an indentation or fold at the fore udder attachment, and increasing DIM. In addition, a low milk urea level was associated with a lower risk of transition to any type of and mild UCD. Cows with previous mild UCD and high-yielding cows had increased risk for a transition to severe UCD. Cows that had an observed transition to severe UCD had an increased risk of veterinary-treated clinical mastitis within 6 wk after the UCD observation. No associations were found between UCD and SCC or hock lesions. The median observed duration of a UCD case was 12 wk, but most cases did not have an observed start or end during the study period. The observed duration of cases including severe UCD was longer than for cases involving only mild UCD. The high incidence and often long duration of UCD emphasize the need for preventive measures and treatment strategies.