Fixed-time artificial insemination (FTAI) programs call for A.I. to be performed at a specific time following prostaglandin (PG) administration. For instance, research has shown that following the 14-day CIDR-PG protocol for heifers, the pregnancy rate is highest when A.I. is performed 66 hours after PG administration. However, I also know that not all heifers express estrus prior to FTAI. For that reason, all heifers enrolled in the 14-day CIDR-PG protocol are given gonadotropin releasing hormone (GnRH) at the time of A.I. Still, research has shown that pregnancy rates are 27 percent lower among females that do not express estrus prior to FTAI.1 That's a significant number.
This all makes me wonder, is that so-called "fixed-time" right for all females? Could timed A.I. pregnancy rates be improved for females not expressing estrus prior to the appointed time for FTAI? These were questions University of Missouri researchers aimed to answer.
University of Missouri researchers have developed an alternative approach to manage timed insemination of cows and heifers that have not expressed estrus prior to FTAI. This approach, known as split-time A.I., delays insemination of non-estrous females until 20 to 24 hours after the scheduled time. Split-time A.I. improved timed A.I. pregnancy rates among beef replacement heifers following the 14-day CIDR-PG protocol2 and among mature beef cows following the 7-day CO-Synch + CIDR protocol.3,4 Use of split-time A.I. following these protocols is diagrammed in Figures 1 and 2.
Estrus Detection Aids
To identify animals that have not expressed estrus, ESTROTECT™ estrus detection aids can be applied at the time of the final PG administration. ESTROTECT patches are designed with a scratch-off coating that is removed progressively as an animal in heat stands to be mounted. Because of this design, producers can have a high degree of confidence about the estrous status of females. In split-time A.I., an animal is considered as having expressed estrus when more than 50 percent of the scratch-off coating has been removed from the ESTROTECT patch (Figure 3).
Split-time A.I. and GnRH
In addition to offering improved pregnancy rates compared to FTAI, split-time A.I. allows for a reduction in GnRH use. Administration of GnRH was not found to be required for cows or heifers with activated ESTROTECT patches at A.I.5 Therefore, insemination can be performed without GnRH administration for cows and heifers that have expressed estrus prior to the standard breeding time, as well as for cows and heifers that expressed estrus prior to the delayed time point.
Questions still remain as to the effectiveness of GnRH administration in non-estrous heifers6; however, it is currently recommended that GnRH be administered to both cows and heifers that have not expressed estrus by the delayed time point.
The 14-day CIDR-PG and 7-day CO-Synch + CIDR protocols have been extensively evaluated in heifers and cows, respectively, and timing of estrus expression following these protocols is very consistent. however, the proportion of heifers and cows expressing estrus prior to the standard breeding time is somewhat variable, as estrus expression is influenced by the cyclicity rate of the herd and other factors, such as weather.
The extent to which pregnancy rates are improved using split-time A.I. compared to FTAI likely varies based on the proportion of cows and heifers expressing estrus prior to 66 hours. Typically, 30-50 percent of mature cows and 20-40 percent of heifers fail to express estrus prior to 66 hours after PG following the 7-day CO-Synch + CIDR and 14-day CIDR-PG protocols, respectively.
In field trials conducted by the University of Missouri, pregnancy rates of non-estrous females were improved 16 percent by delaying insemination 20 to 24 hours. Tables 1 and 2 compare data from field trials using split-time A.I. and FTAI in heifers and cows.2,4
Potential improvements in pregnancy rates appear to be dependent on estrus expression occurring during the 20- to 24-hour delay period. Large data sets for timing of estrus expression in heifers following the 14-day CIDR-PG protocol suggest a sizable proportion of the synchronized group of heifers express estrus during this delay period (Figure 4). Interestingly, further consideration of these results suggested that pregnancy rates achieved using split-time A.I. were similar to those achieved when A.I. was performed based on detected estrus over a six-day period.
In results from the University of Missouri, 55 percent of both heifers and cows that had failed to express estrus by 66 hours after PG went on to express estrus by the time delayed A.I. was performed.
Split-time A.I. has not been evaluated extensively with protocols other than those described here. Because the timing of estrus expression varies from protocol to protocol, it is unknown whether pregnancy rates to split-time A.I. are improved over FTAI following the administration of other protocols.
When using split-time A.I. rather than FTAI, two additional costs are incurred: the cost of the ESTROTECT estrus detection aids and the cost of the additional labor for animal handling at the delayed time. However, cost savings are realized for the GnRH product because animals with activated estrus detection aids do not require GnRH administration. Total estrous response when using split-time A.I. is frequently 85 percent or higher (see cumulative response by 90 hours after PG in Figure 4). Therefore, the cost associated with GnRH administration is likewise reduced by 85 percent or more. This GnRH cost savings alone typically offsets the ESTROTECT and additional labor costs.
Most importantly, the increase in pregnancy rates (generally an increase of 5 percent or more for the synchronized group overall) using split-time A.I. offers additional value to producers, as markets have shown heifers carrying an A.I. pregnancy command higher prices than those carrying a natural service pregnancy.
Table 3 presents a cost scenario in which split-time A.I. rather than FTAI is used for 100 heifers. For the additional animal handling, labor costs are estimated based on four people working two hours at $10 per hour, for a total of eight man-hours. Estrus detection aids can range in price based on the quantity purchased but are estimated at $1.30 per patch in this analysis. Cost of GnRH product likewise varies based on manufacturer and quantity purchased but is estimated at $3 per dose in this analysis. Conservatively, use of split-time A.I. can be expected to achieve five or more additional A.I. pregnancies per 100 head. In this analysis, the value of an A.I. pregnancy is assumed to be $211, based on the average premium associated with heifers carrying an A.I. versus natural service pregnancy among heifers selling in the Missouri Show-Me-Select Replacement Heifer Program from 2010 to 2015.
Timed A.I. pregnancy rates can be optimized through use of a split-time A.I. approach following administration of the 14-day CIDR-PG protocol for heifers and the 7-day CO-Synch + CIDR protocol for mature cows. ESTROTECT estrus detection aids applied at the time PG is administered allow producers to determine the estrous status of females and inseminate at an optimal time. Moreover, split-time A.I. facilitates a reduction in GnRH use, as producers can limit GnRH administration to only those females that have not expressed estrus by the time of delayed insemination.
References available upon request.