Virginia Cooperative Extension - Knowledge for the CommonWealth

When is the best time to breed cows AI for optimal pregnancy rates?

by Ray L. Nebel
Extension Dairy Scientist, Reproduction

Dairy Pipeline: March 1997

We have just concluded a study using 17 herds which utilized the electronic estrus detection system, HeatWatch®, to determine the optimal time to inseminate. To make a long story short, the highest pregnancy rates were obtained for breedings that were 4 to 16 hours after the onset of heat or first standing event. The problem for most dairy producers is determining when the beginning of standing heat occurs. Approximately half of all heat periods are missed on the average dairy farm. Occurrence of the first stand is almost impossible to know without the use of a system that provides 24-hour surveillance. For the herd without a 24-hour surveillance system when is the best time to breed? Timing of AI should be based on the frequency of observations for standing heat. In herds where observations occur less than four times daily, AI should be performed within 4 to 6 hours after first observation. In herds where observations for heat are more frequent (more than three times per day) breeding should occur approximately 6 to 12 hours after first observing standing heat. Therefore, the frequency of visual observation for signs of heat should determine when cows will be bred after detection. This also explains why once-a-day AI and inseminations following the a.m.-p.m. guideline are usually not different. On most farms the frequency of visual observation periods are not sufficient to obtain optimal pregnancy percentages because timing of AI is not accurate. Without accurate knowledge of the onset of mounting activity, timing of AI is at best a good guess.

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