Interrelationships between production and reproductive diseases in Holstein cows. Age and seasonal patterns.

Influences of age and season on occurrence of dystocia, retained placenta, metritis, cystic follicle, and luteal cyst were studied retrospectively. The 6 yr of data were from 2960 lactation records of 1401 registered Holstein cows from 20 commercial herds that participated in the dairy herd health program of the Ontario Veterinary College. For each disease, odds ratio analyses compared the risk of disease in each age group to the risk in all other age groups pooled. The following age groups were at increased risks of diseases: dystocia, 2 to less than 4 yr; retained placenta and metritis, 7 to less than 10 yr and 10 or more yr; cystic follicle and luteal cyst, 10 yr or more. For all diseases except dystocia, age 2 to less than 4 yr was at decreased risk. Formal statistical methods were used to test for unimodal seasonal patterns in monthly calvings, in monthly disease incidence (number of diagnoses), and in risk (lactational incidence rate) of disease according to month of calving. There were the following significant peaks: fall calvings in the age group 2 to less than 4 yr, summer-fall risk of metritis, fall-winter incidence of dystocia and metritis, and fall-winter risk of dystocia.