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Untangling the pregnancy rate equation

Joel Pankowski Published on 10 October 2012

Over time the knowledge and ability necessary to get cows bred have taken tremendous strides forward, bringing with them greater on-farm success.

Reproductive success takes effort from every angle of the dairy and starts with an understanding of pregnancy rate and the factors which impact it most.



Untangling the equation

In the past, pregnancy rate has been evaluated by looking at the percentage of cows bred during a 21-day heat cycle and confirmed pregnant.

Rather than looking at the equation in three-week increments, dairy producers can learn more about herd pregnancy rate by further investigating what is included in the equation in Figure 1
Figure 1. Evaluating pregnancy rate by focusing on heat detection rate and conception rate separately can allow you to better evaluate where change can be implemented to see improvements.

Table 1
Table 1
outlines some of the influencers on heat detection rate and conception rate.

Reproductive technology advancements have helped dairies improve the precision and rate of heat detection significantly in the past few years and changes can be seen as quickly as two to three estrous cycles.

Conception rate is much more complex because it is impacted by many areas of the dairy operation and variables that are hard to control.


Improving conception rate requires a commitment and investment from the dairy producer.

Boosting conception rate with the ration

One area that can have a profound effect on the cow’s ability to conceive is nutrition. Many key parts of the ration – like energy levels – will directly impact the dairy cow’s ability to become pregnant.

After all, reproduction is a luxury that can only be achieved when the proper ration and environment fulfill maintenance and milk production requirements.

Within a properly balanced diet, specific supplements can help improve conception rates and reproductive success.

Table 2
One tool nutritionists have identified is Omega-3 and Omega-6 essential fatty acids (EFAs). EFAs aid in several significant biological functions. (See Table 2.)

On-farm research confirms the benefits of a ration supplemented with bypass Omega-3 and Omega-6 EFAs.


In the trial, cows fed bypass EFAs had higher pregnancy rates by five percentage points. Since heat detection was similar between the two groups, the improved pregnancy rate was achieved through an enhanced conception rate.

Adding EFAs to the dairy cow’s ration has additional benefits that can impact the reproductive success of your herd. Omega-3 and Omega-6 EFAs can optimize immune function, enhance visible signs of heat and reduce incidence of metabolic disorders postpartum.

The pregnancy rate in summary

An optimal pregnancy rate and reproductive success take efforts from all areas of the dairy.

Work with those involved on your operation and your herd nutritionist to identify opportunities for improvements, keeping in mind:

  • Pregnancy rate is the product of both heat detection rate and conception rate.

  • Reproductive advancements allow for heat detection rate to improve more simplistically, whereas conception rate is impacted by a variety of variables.

  • Conception rate is affected by multiple factors and is a long-term investment.

  • Dairies should isolate their conception rate and heat detection rate to fully understand where change can be most impactful.  

Examine conception rate independently

Each day dairy producers evaluate and analyze herd reproduction to see where gains can be made. Untangling the pregnancy rate equation can help you better understand where change is taking place.

To help explain this concept, look at this data from a 1,100-cow Midwest U.S. dairy that has increased herd pregnancy rates by feeding a ration supplemented with bypass Omega-3 and Omega-6 EFAs.

The dairy decided to investigate if the nutritional change was really the variable making the difference or if other factors – like heat detection – improved herd performance.

Midwest dairy conception rates September 2009 - June 2011
Figure 2
pulled from the dairy’s DairyComp 305 records compared conception rates from before and after the ration change.

Click here or on the image at right to view it at full size in a new window.

The horizontal line in the chart represents the average herd conception rate prior to the ration formulation and the vertical line represents the beginning of supplementation.

It was concluded the month-by-month comparison and overall conception rates increased when bypass Omega-3 and Omega-6 EFAs were fed.

References omitted due to space but are available upon request. Click here to email an editor.

Pankowski has more than two decades of technical on-farm support experience and currently consults with nutritionists and dairy producers in the Northeast and Midwest regions of the U.S.

Dr. Joel Pankowski