Is it really worthwhile to improve? In November 2010, the calving interval at Drahoka Farm was 444 days. Each open day subtracted from the calving interval generates a gain of $3 to $6 per cow. A target of a calving interval of 400 days offers a potential gain of $16,230 per year for the herd. Learn more about the process that enabled Ferme Drahoka to improve reproduction management in the herd and increase profitability.