Epidemiological and economic study of the repeat breeder syndrome in Michigan dairy cattle. I. Epidemiological modeling

Abstract

Two models of repeat breeder syndrome (RBS) were developed using data obtained from dairy herds participating in the National Animal Health Monitoring System (NAHMS) in Michigan. These models were designed to study the relationship between RBS and six common risk factors: (1) herd characteristics and environment; (2) nutrition during the dry period; (3) diseases which occurred within 72 h of calving; (4) diseases which occurred more than 72 h after calving; (5) reproductive management; (6) milk production. In Model 1, principal components analysis was used to examine the interrelationships among the risk factors. The variable-synthesis approach was used to combine related risk factors into one common risk factor. Herd characteristics and diseases which occurred within 72 h of calving were significant determinants of RBS ( P≤0.01).Milk fever, dystocia and retained placenta occurred as a complex and contributed the most to the cumulative incidence (CI) rate of RBS. In Model 2, a path model was developed to display and to quantify the associations among the significant risk factors that were obtained from Model 1. Dystocia was positively associated with the CI of RBS directly. Milk fever was associated with RBS indirectly through dystocia. Increasing the proportion of corn silage to alfalfa in rations fed to dry cows was associated positively with the CI rate of milk fever and was associated negatively with the CI rate of dystocia. Results of this study suggest that the ration of the dry cow should be balanced in order to prevent dystocia, milk fever and RBS.