Epidemiology of reproductive performance in dairy cows

The objectives of this presentation are to review results of our previous a nd on-going research with respect to the risk factors and consequences of p oor reproductive performance in dairy cows, and to develop an economic fram ework to optimize decisions related to dairy cow reproductive performance. To make profitable breeding and replacement decisions, the farmer must acco unt for factors including age, production level, lactation stage, pregnancy status, and disease history of the cows in the herd. Establishing the inte rrelationships among disease, milk yield, reproduction, and herd management is necessary for developing a decision model for disease treatment, insemi nation, and replacement. The data for the studies reviewed in this presentation incorporate health, production, and management components from Holsteins in the Northeast USA a nd Ayrshires from Finland. Data were analyzed using the Cornell Theory Cent er Supercomputer. The effect of risk factors on reproductive disorders was modeled with logistic regression, and on conception, insemination, and cull ing with survival analysis. The effect of reproductive disorders on milk yi eld was analyzed with mixed models. Economic optimization of reproductive p erformance was done with dynamic programming (DP). High milk yield, high parity, and calving in winter were risk factors for s everal reproductive disorders. These disorders, in turn, delayed inseminati on and conception in dairy cows, and some of them increased the risk of cul ling. Dystocia, retained placenta, and early metritis led to a short-term d rop in milk production. High milk yield was not a major factor in delaying conception, except in first parity cows. However, higher yielders were more likely to be inseminated, and less likely to be culled. Non-pregnant cows had a higher risk of being culled. Reproductive performance of dairy cows influenced a herd's profitability, a nd good heat detection and conception rates provided opportunities for mana gement control. It was not always economically advantageous to get cows pre gnant as soon as possible, and there was no one optimal value for the calvi ng interval length for all cows in a herd. (C) 2000 Elsevier Science B.V. A ll rights reserved.