Epidemiology of reproductive disorders in dairy cattle: associations among host characteristics, disease and production

Abstract

Logistic regression was used to investigate the effects of host characteristics, production and 23 veterinary diagnoses on the risks of 10 reproductive disorders. For each reproductive disease in each lactation record, all prior disease events in that lactation were examined as possible risk factors. To make an equal opportunity for risk-factor diseases to be counted as present in both cases and controls, a dummy days in milk (DIM) variable was assigned to control records. The assignment was random, but in proportion to the distribution of the DIM for the cases of that disease. The data set was based on 61 124 Finnish Ayrshire cows, from milk-recorded herds, who calved during 1983. Each cow was under observation for 2 days before calving to the following calving or to removal from the herd. Twenty percent of the cows were treated by a veterinarian for reproductive disorders. Lactational incidence rates (%) were: dystocia, 1.2; prolapsed uterus, 0.2; retained placenta, 4.4; early metritis, 2.3; silent heat, 4.9; cystic ovary, 6.8; prolapsed vagina, 0.1; late metritis, 1.1; other infertility, 2.1; abortion, 0.4. The risk of silent heat and other infertility decreased and the risk of dystocia (after the first calving), retained placenta and ovarian cyst increased with increased parity. Parity did not explain the incidences of the other reproductive disorders. The cows calving during September-February (the dark season) had higher risks of early metritis, silent heat, cyst and other infertility than those calving during the light season. Higher herd milk yield in the previous lactation increased the risks of retained placenta, early metritis and late metritis; higher herd yield in the current lactation increased risks of dystocia and of ovarian cyst. The risks of retained placenta, early metritis, silent heat, ovarian cyst, other fertility and abortion also increased with increased individual-cow's milk yield. Most reproductive disorders were interrelated. Six non-reproductive disorders (non-parturient paresis, udder edema, indoor and outdoor hypomagnesemia, rumen acidosis and chronic mastitis) were not risk factors for any of the reproductive disorders. Of the other non-reproductive disorders, clinical parturient paresis was a risk factor for dystocia, prolapsed uterus, retained placenta, and early metritis; clinical ketosis was associated with silent heat, cystic ovary and other infertility; disorder of the abomasum, traumatic recticuloperitonitis, acute mastitis and foot or leg injury also contribited to early metritis. No disorders were protective.