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Monitor open dairy cows

Contributed by Donna M. Amaral-Phillips Published on 14 November 2019

Dairy cows that become pregnant within a reasonable time frame produce more milk over their lifetime and are less likely to be culled from the herd. Thus, the goal is to have as many cows pregnant as possible by the time they are less than 150 days in milk.

Various researchers have calculated the cost of additional days open. The actual cost varies depending on heifer replacement costs, value of cull cows, age of the cow being culled and the number of days cows are open. Although each researcher calculates a different cost, they all agree that there is a “cost” associated with extended days open. The more cows with extended days open, the greater the total cost. No great surprises here. But closing this gap in getting cows bred and pregnant is a controllable management component.



Various tools and practices can be used to detect cows in heat and those cows that should be bred. Heat detection can be accomplished through routine, planned visual observation (three, 30-minute observation periods daily), use of heat detection aids or through an activity monitoring system. Maintaining and using production and breeding records for individual cows is important to determine the best day in milk to start breeding a cow and whether they have been bred.

The most important controllable component in a breeding program is to identify open cows and to do something about getting them pregnant. Open cows include not only those not bred past the voluntary waiting period, but also those not currently pregnant, even if they have been bred. The earlier these cows are identified, the quicker they can be rebred (or bred) to decrease the total number of days open. Routinely having a veterinarian palpate or ultrasound bred cows or collecting milk or blood for testing for compounds associated with a pregnancy is the best way to determine cows that are open, not whether they have not come back in heat. (Pregnancy diagnosis does require that cows are at least 28 to 35 days pregnant, depending on the test or veterinarian.)

Generally, pregnancy diagnosis is recommended for herds every two to six weeks, not every two to six months. Your veterinarian can help select the best frequency needed. In herds using natural service (bull-bred herds), routine pregnancy diagnosis is as important, if not more important, as those herds using A.I. Pregnancy checks help determine not only those cows open or pregnant, but also an estimated breeding date to use when calculating a dry-off and expected calving date.  end mark

—Reprint from University of Kentucky Extensions

Donna Amaral-Phillips
  • Donna Amaral-Phillips

  • Extension Dairy Nutritionist
  • University of Kentucky
  • Email Donna Amaral-Phillips