Veterinarian View | April 2025

Increasing Pregnancy Rates with Fixed Time Artificial Insemination

contributed article by Dr. Vince Collison, Collison Embryo and Veterinary Services,

Rockwell City, Iowa

As we go into the spring, it is time to focus on our AI and ET programs now that calving is almost over. Fixed timed artificial insemination (FTAI) is a method where all cows or heifers are bred at the same time after being synchronized. This is usually 60 to 66 hours after pulling a CIDR for cows and 54 to 60 hours for heifers.

This works fairly well, and I tell producers that they should expect about a 50 to 60 percent pregnancy rate with this strategy. For owners who want to utilize a timed AI program but would like to increase their percentages of pregnant females, there are a couple of variations.

Early Heat Detection

Do some heat detection early. If a cow is showing signs of estrus in the range of 24 to 48 hours after pulling a CIDR, it would probably increase their chances of becoming pregnant by performing AI earlier. Especially for a cow which won’t be bred via AI until 60 to 66 hours. For cows, shoot to AI in a range 8 to 13 hours from the start of standing heat. If that falls before the appointed time to AI, I would get her AIed early to increase her chances. For heifers, we usually perform FTAI earlier, so there probably won’t be as many that this applies to.

Hybrid FTAI

Use a hybrid FTAI where you will heat detect out to 72 to 84 hours and then time breed any cows or heifers that have not shown heat yet. This gives every female a chance to show heat and time the AI around the start of standing estrus. So, if we were to heat detect out to 84 hours, any female that is found standing at this time will wait to be AIed 12 hours later and all females that are not in standing heat will be AIed at 84 hours. In some cases, I will even extend this time out to 96 hours, especially with heifers.

Split Time AI

One strategy that has worked very well for us is split time AI. With this method we will AI all females that are in standing heat at 60 to 66 hours. We will apply an estrus detection aid at the time we pull CIDRS to make this easier to determine on the first day of AI. We then will come back 24 hours later, and time breed all the other females that were not in heat on day one. Usually many of these cows and heifers will be in heat by the second day.

This program has usually resulted in a higher percentage of females pregnant than a FTAI done all in one day. We usually give all females that are synchronized a GNRH injection on the first day of AI, but for the cows or heifers that don’t show heat on the first day, you can wait to give them their GNRH injection on day two when they are AIed.

If you want to use sexed semen to optimize pregnancy success, it is recommended to use sexed semen only on females that have exhibited estrus by the first or second AI and only conventional semen on females that have not exhibited estrus.

Also, when using any timed breeding program, the sire can make a lot of difference on pregnancy rates. Many AI companies will have data on the bulls they offer, showing which ones may work better in a FTAI program.

Additional Recommendations

For all programs, for best results when performing AI off of heat detection we recommend:

• With conventional semen, AI cows 8 to 13 hours after the start of standing heat.

• With conventional semen, AI heifers 12 to 16 hours after the start of standing heat.

• With sexed semen, AI 16 to 22 hours after the start of standing heat for cows and 20 to 24 hours for heifers.

• Perform vaccinations with any modified live pre-breeding vaccines at least 30 days prior to starting a synchronization program.

Many details go into a successful AI program. Often many decisions on how soon to AI a cow or heifer are very subjective. If someone is trying to decide whether to AI a cow or heifer that night or wait until the next morning, I will usually AI a cow that night and wait to AI a heifer the next morning. This is based on ovulation patterns of cows and heifers.

Cows will ovulate sooner and are usually fertile in the second half of their standing heat. Whereas heifers ovulate later and are still fertile even after they have come out of heat. For many producers with these variations of FTAI programs, pregnancy rates can rival those of a program that is 100 percent based off of heat detection.

learn more www.collisonembryoservices.com

Dr. Vince Collison is co-owner of Collison Embryo and Veterinary Services PAC

in Rockwell City, Iowa.