When is the Best Time to Inseminate Cows and Heifers?

For those of us who have been involved in breeding our cattle through A.I. for a while, the advantages are clear.  Of course, the challenges to building a successful A.I. program are also clear.  While there are a number of issues that need to be addressed, in general there are four main components to a successful A.I. program:

  • Healthy and nutritionally sound cattle
  • Quality semen; stored and handled properly
  • Experienced A.I. technician
  • Accurate heat detection followed by timely breeding (the most difficult aspect)

Obviously, it is critical to know when cows are in heat.  There are many heat detection aids on the market that will help to identify those cows in heat.  However, just knowing that a cow is in heat is not enough.  It is equally as important to know precisely when a cow comes into heat to determine the ideal time for the A.I. service.

Several years ago, I conducted a field study modeled after a dairy cow project performed by Dr. Ray Nebel at Virginia PolyTechnic.  The goal was to evaluate time-to-insemination in over 2,500 bos taurus females.  We utilized a first generation electronic mount detection system.  We also used a software algorithm developed by Dr. Nebel in his previous study.  The algorithm looked for mounting patterns indicative of true estrus as opposed to false positives.  It is the same algorithm we currently use with the AccuBreed™ wireless heat detection system.  The criteria for a cow to be declared in heat is 3 mounts in 4 hours with each mount being two seconds or greater.  When the criteria are fulfilled, we refer to the first mount in the three mount sequence to define the onset of heat.

If a cow is mounted at 8am and then at 3pm, 3:15pm and 3:45pm, the 8am mount will be disregarded as part of the criteria and AccuBreed will declare the 3pm mount as the onset (the 8am mount did not fall into the 3 mounts in 4 hours criteria).

(Click on image to expand.)

Now let’s take a look at the best time to breed according to the chart below.  We tracked how many hours had lapsed from the declared onset of heats to the actual A.I. service.  One of the interesting things we learned had to do with the old “12 hour rule”.  Many of us had grown up with that rule that states the best time to breed your cattle is 12 hours after onset (of course, that assumes you know when each cow actually came into heat).  So while the 12 hour rule is still valid, we now know there is a range of optimum times to breed.  If you breed your cows 10-16 hours after the onset of heat, you will see very little difference, if any, from breeding them at 12 hours post onset.

The other interesting fact is that this study was performed on bos taurus cows only.  Are we going to see time-to-inseminate differences with heifers?  What about dairy cows and heifers?  What about bos indicus cattle?  And then there’s the issue of time-to-insemination when using sexed semen.

In the next AccuBreed™ blog, we will discuss these questions as well as examine the particular elements that make breeding at the right time so important.

Happy heat detecting!

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