Economic Value of Days Open for Holstein Cows of Alternative Milk Yields with Varying Calving Intervals

Abstract

The value of days open was estimated by budgeting simulation of a commercial herd situation for Holstein cows of alternative milk yields with varying calving intervals. Values for days open were differences of income over feed cost per cow per day among alternative calving intervals of 12, 13 and 15 mo. Producing abilities for milk of cows corresponding to a 13-mo. calving interval were 5900, 6800, 7700 and 8600 kg 3.5% milk per 300-day lactation. Conditions of herd management were a fixed policy of 65 days dry, herd size of 120 cows, group feeding with income-maximizing rations solved by linear programming, and a herd age structure of 30% of cows < 36 mo. and 70% of cows .gtoreq. 36 mo. The effect was little on annual income over feed cost in the short run for modest increases or decreases of calving interval. Depending on milk producing ability, minor positive or negative differences occurred by increasing calving interval from 12 to 15 mo. There was a positive value per day open for all milk producing abilities when calving interval was increased from 12-13 mo. and a consistently negative value per day open when it was increased from 13-15 mo. Thus, the 13-mo. calving interval appears to be close to optimal. Cost associated with changes in either direction from 13 mo. were small enough not to be a major management issue when cows were grouped and fed according to milk yield and when dry period was 65 days.