Dairy Herd Improvement Association (DHIA) milk production records are estimates of total production based on the production recorded only once each month for each animal. The milk from each milking is weighed on a spring scale and the individual milk weights are summed to obtain a daily-total. The daily production is multiplied by the number of days in the month, and the pounds of milk credited for the individual months are then summed to obtain animal lactation totals. These practices have brought up the questions of whether (1) sampling a cow's production once monthly provides an accurate estimate of the total lactation and (2) if DHIA-accepted measuring devices contribute much error to these estimates. The relative impact of a random error on the precision of DHIA records is determined by the magnitude of the existing error variance due to day-to-day variation in yield. This study with Holstein cows was to determine the magnitude of daily variance in dry-lot milk production.

Reliance Milk Farms in Delano made their milking facilities available for 10 days during the collection of data utilized in this trial