Abstract
Disease occurrences and risk factors for the most common diseases among 39,727 Finnish Ayrshire dairy cows belonging to 2338 herds were studied. All the cows calved during 1993 and were followed until the next calving or culling. Lactational incidence risks, recurrence of, and number of treatments required for one episode of a disease are described for 17 different veterinary diagnoses. The 5 most common diseases and their lactational incidence risks were: acute mastitis (17.0%), anestrus (8.1%), ovarian cysts (7.3%), milk fever (5.4%), and ketosis (4.9%). The highest recurrence probability (14.2%) was observed for acute mastitis, followed by fertility disorders. Milk fever was the one disease that required the most repeated treatments, i.e., almost 30% of the cows were treated at least twice, whereas for most of the other diseases about 10% of the cows required more than one treatment per first episode of the disease. Logistic regression models were fitted to study the effect of milk yield and other risk factors on the occurrence of the 5 most common diseases. Increasing milk yield was found to be a risk factor for acute mastitis, ovarian cysts, and for anestrus among older cows (parity > 2), and for milk fever among younger cows (parity = 2). Several diseases were found to be risk factors for other diseases.