Effects of Days Open Days Dry, and Season of Freshening on Income over Feed Cost and 305-Day Mature Equivalent Milk Yield, for Three Different Production Levels

Abstract

ABSTRACT Days open, days dry, and season of calving were examined to maximize Income Over Feed Cost (IOFC) and 305-d mature equivalent milk production for three different production levels. Models with all fixed effects were analyzed using SAS® PROC GLM for 50,743 Holstein cows from 4687 herds calving in yr 1990 and 1991. Production level of cow was not important to determine optimum days open to maximize 305-d milk yield, but was important for days open to maximize IOFC. For 305-d milk yield, days open of 91 to 105 d, 76 to 90 d, and 61 to 75 d were optimum for cows calving in season 2 (February through April), season 3 (May through July), and season 4 (August through October) respectively. For IOFC, optimum days open was 15 d higher for average and above average production levels for seasons 2 and 3 than for below average production level. Optimum days open to maximize IOFC for calving season 4 was 15 d higher for above average production level than for below average and average levels. Cows calving in season 2 had highest optimum days open. Conclusive results could not be obtained for season 1 as less than 10% of records in the data set belonged to that season and of those only 10% had an open period shorter than 150 d. On average, cows calving in season 3 yielded highest IOFC, which was $667, $482, and $276 more than cows calving in season 1 (November to January), season 2, and season 4 respectively. The 305-d milk yield was not different for the four seasons of calving.