Effect of Length of Calving Intervals on Income Over Feed and Variable Costs

A budgeting procedure using a microcomputer spreadsheet program was used to determine the effect of calving intervals on income over feed and variable costs using various milk yields of cows, milk and feed prices, and culling strategies based on either age of cow or lactation number. When the culling strategy was based on age of cow with a $12 milk price and low feed prices, income over feed and variable costs of cows during a 13-mo calving interval was slightly lower than those during a 12-mo calving interval. Losses for each additional day of calving interval from 12 to 13 mo, and thus day open, ranged from 0 to $.13. Increasing the calving interval to 14 mo increased the losses per day open with a range of $.10 to $.71 in comparison with a 12-mo interval. Losses per day open for a 15-mo calving interval ranged from $.18 to $.60 in comparison with a 12-mo interval. Factors that reduce income over feed costs, such as lower production, lower milk prices, higher feed prices, and culling at an earlier age decrease the loss in income over feed and variable costs for 14- and 15-mo calving intervals in comparison with a 12-mo interval. When the culling strategy was based on lactation number, extending the calving interval increased the income over feed and variable costs with the greater effect occurring between 12 and 13 mo. From these results, recommendations for a 12- to 13-mo calving interval appear justified.