Interrelationships between production and reproductive diseases in holstein cows. Path analysis.

Path models were constructed to investigate causes and effects of dystocia, retained placenta, metritis, cystic follicle, and luteal cyst. The general model included 12 variables: five diseases, age, previous and current breed class average for milk, previous and current days in milk, days dry, and calving interval. The general model indicated 40 bivariate relationships (34 allegedly causal). Restricted models were derived. These included all variables except dystocia (possibly because the set of 810 lactation records excluded data on primiparous cows) and 26 bivariate associations (20 causal). In these models, breed class average, days in milk, and dry period in the previous lactation had little effect on disease. The most important cause and effect relationship among the diseases was retained placenta causing metritis. Excluding dystocia, all of the diseases caused increases in calving interval (16.79 to 35.82 days), in the breed class average for milk (.50 to 6.51 points), and in days in milk (8.72 to 19.73 days). Most increases in the breed class average were of less than 2 points and were mediated by the increase in calving interval (days open); however, there was a direct effect of cystic follicle on the breed class average for mild of +5.58 points (+297 kg).