How to Age a Calf Fetus

An estimation of fetal age can help you better manage your calving season. Knowing the age of the fetus enables you to determine the stage of gestation.

 This in turn allows you to:

  • Observe cows around their projected due dates so that intervention can be provided when required; for example, a Caesarean can be performed on a cow with twins if necessary to improve the possibility of delivering two live calves
  • Sort cows into different feeding groups to optimize the nutrition they receive at each gestational stage
  • Optimize the dry period in dairy cattle to minimize the impact of negative energy balance in the immediate post-partum period which can impact milk yield

Fetal age is determined by measurements taken on an ultrasound image referencing an aging chart. There are four different measurements that you can use based on the view you see of the fetus. They are: trunk diameter, head diameter, crown rump length and head length.

In this video we will age the fetus using the crown to rump measurement.



Often, people believe that there is an equation with the number of squares to the age of the fetus. However, that is not an accurate way of calculating fetal age. Fetal aging takes practice, repetition, and reference to an aging chart. You can find the aging chart here, or you can download are aging app here. Or, with our new wireless Easi-Scan:Go you can automatically calculate fetal age using the calipers. 

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2019 American Association of Equine Practitioners Mummified Bovine Fetus

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