Relationship of Age at First Calving, Days Open, Days Dry, and Herdlife to a Profit function for Dairy Cattle

Abstract

Relationships of breeding and management factors to economic return for dairy cows were studied in lifetime records from 933 Holstein cows. A profit function was defined from milk production, body weight, reproductive performance, herdlife, and prices for feed energy, milk, calves, salvage value, and fixed costs. Statistics on individual cows were milk yield, days in milk for each lactation, fat percent, weight at first calving and maturity, number artificial inseminations, and age at each calving and at disposal. Values of each trait maximizing a second trait are defined as optimal. Optimum percent days open and days dry were 31.0 and 10.5 for profit per day-herdlife. Slightly larger percentages were optimal for total performance traits, profit-life, milk-life, and herdlife. Optimum age at first calving for total lifetime performance was 22.5 to 23.5 mo. Profit per day of herdlife was $.05 larger for cows calving during the 25th mo of age than those calving earlier. Days open, days dry, and age at first calving accounted for 10.0, 4.5, and .9% of variation in herdlife; for 4.3, 18.8, and .6% in milk per day-life; and 8.1, 8.3, and 5.2% of variation in profit per day-herdlife. Correlations between age at first calving with percent days open and herdlife were .05 and −.10. Maximum profit per day-herdlife was expected for cows with 25 mo of age at first calving, 124 days open, and 42 days dry while maximizing milk per day-life and herdlife. © 1976, American Dairy Science Association. All rights reserved.