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Synchronization of Estrus with Heatsync
by Darrel J. Kesler and Teresa L. Steckler


  • HeatSync will synchronize ovulation in dairy cows with greater expression of estrus than OvSync; however, it has not been demonstrated to be more effective than OvSync.


During the past several years, several producers have used OvSync to synchronize ovulation and facilitate timed AI. More recently newer procedures have been introduced and discussed. One of the newer procedures receiving considerable attention is HeatSync. The purpose of this article is to describe how HeatSync is carried out, provide the available data on the procedure particularly as it compares to OvSync, and to give the advantages and disadvantages of this procedure.


HeatSync is a slight modification of OvSync. The OvSync procedure involves the administration of GnRH seven days before an injection of PGF2". The injection of GnRH provokes either atresia or ovulation of antral follicles. PGF2" then induces luteolysis of any luteal tissue, whether they be from a spontaneous ovulation or the GnRH-induced ovulation seven days earlier. OvSync then utilizes a second injection of GnRH 48 hours later to provoke a timed ovulation. HeatSync employs an injection of ECP 24 hours after the injection of PGF2" rather than the second injection of GnRH. HeatSync then requires timed AI 48 hours later—72 hours after the injection of PGF2".


HeatSync studies have only been conducted in Florida and Texas. There were 371 cows included in the study conducted in Florida and 321 cows included in the study conducted in Texas. Both studies included a positive control group which consisted of OvSync. Pregnancy results at the two location are summarized in the following table (Table 1).

Table 1. Pregnancy rates of cows administered OvSync or HeatSync for the synchronization of estrus.

Item OvSync HeatSync
Pregnancy Rate:    
Florida 37% 35%
Texas 28% 29%
Estrus Rate:    
Texas 18% 65%

Although there has been considerable discussion on this new procedure, these results do not suggest that HeatSync results in higher pregnancy rates. In fact, the pregnancy rates were nearly identical. The difference between the two procedures is that there is a higher estrus response in cows synchronized with HeatSync vs. OvSync. Several have expressed concern that cows administered OvSync do not express estrus. This is because the second injection of GnRH is administered, in most cases, before the expression of estrus and once administered provokes an preovulatory LH surge. Once the LH surge occurs, estrus will be inhibited because the follicular cells are luteinized to become progesterone synthesizing cells rather than estradiol synthesizing cells. Ovulation is provoked in the absence of ovulation without any adverse effects on fertility.

As HeatSync is a new procedure, limited data are available. OvSync, on the other hand has considerable data available. The following table (Table 2) is a summary of 17 studies summarizing pregnancy rates of OvSync treated cows. The submission rate, based on the protocol, is 100%—all cows are inseminated. The comparison to HeatSync is biased because there is simple far more data available for OvSync. However, the important point here is that OvSync works nearly every time. An estrus/ovulation control procedure must not only have a good average pregnancy rate, but there must be minimal variability associated with the procedure. OvSync is effective on both counts.

If estrus is what you want, you may want to use HeatSync. Furthermore, HeatSync cows will have greater uterine tone that will facilitate insemination. However, if you don’t have facilities with good footing capacity, you may not want to use HeatSync or you may have cows with injuries associated with the expression of estrus. Also, it has been recommended that cows that express estrus 24 hours after the injection of ECP be bred by the AM/PM rule rather than waiting for the timed AI requiring estrus detection—not required for the OvSync procedure.

Table 2. Pregnancy rates of cows administered OvSync from 17 published studies.

Item OvSync HeatSync
Pregnancy Rates 37% 32%
Number of herds 17 2
SE (variation) 2.0 3.0
Range (Mean +/- 1 SD; 67% herds) 29-45% 28-36%

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