Dairy Herd Improvement Test Research Articles

Effects of Days Dry and Days Open on Holstein Milk Production

Holstein lactation records from the Dairy Herd Improvement test day files of the New York Dairy Records Processing Laboratory of Cornell University were used to study genetic and environmental relationships of days dry and days open with milk production.Age and month of calving significantly influenced lenhth of dry period. Within herd heritability estimates of days dry were .15, .33, and .34 for second, third and later lactations.Within herd heritability estimates of days open were essentially zero. As the length of open period increased, cumulative milk production also increased at each successive stage of lactation. Differences of days open groups for 305-day milk yield were used to prepare adjustment factors for days open.