Cumulative Net Income Curve of the Dairy Cow

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Abstract
An updated version of a dynamic model of a dairy herd was described. Data from 3332 simulated calving intervals were utilized to estimate coefficients for a quadratic equation describing cow cumulative net income during the calving interval. A cumulative curve describing total net income to a specificed number of weeks after freshening was analyzed with its derivative describing income per week at a specified number of weeks after freshening. Young cows obtained peak income before mature cows with mature cows producing positive values for weekly income 3.7 wk longer than first lactation heifers. Health problems that occurred soon after freshening decreased the intercept of the quadratic equation with a persistent effect on cumulative income throughout lactation. Milk and feed prices, cow breeding value, and health disorders observed throughout the calving interval influenced primarily the linear coefficient, resulting in a cumulative effect, which increased through the lactation. Significant quadratic coefficients were observed when the effect on income varied early and late in the calving interval. Days open and infertility, which influence income in late lactation, also significantly affected the quadratic coefficiently. There is a need for complete data on cow income from commerical herds to study further the factors affecting the pattern of dairy cow cash flow.