Artificial insemination (AI) of dairy heifers provides numerous advantages to the dairy producer. Foremost is the opportunity to improve the entire herd’s genetic merit. USDA Holstein Sire Summaries document that an average first-evaluation AI sire has a Net Merit Dollars advantage of $72 per lactation over an average natural service bull. Related to the genetic merit from the sire component is the fact that heifers born of AI matings are genetically the best animals in the herd. These AI-sired heifers provide more quality replacements and a greater opportunity to cull animals of lower genetic merit. Approximately 30 percent of calves born each year are progeny of first-calve heifers. Heifer AI has a major impact on genetic improvement of the entire herd.
Merchandising is another advantage for AI-sired heifers. If quality AI-sired replacements are available, then dairy producers can sell heifers based on genetic criteria. In addition, heifers tend to be the most fertile females in the herd, thus they are more likely to conceive to AI. These advantages document the tremendous opportunity that exists with use of AI for heifers.
The fact that the AI sires are examined and tested for reproductive soundness and disease, and that semen quality and fertility are routinely monitored are additional benefits. Based on the results of breeding soundness examinations performed on sixty-six on-farm dairy bulls by one veterinary clinic in California, 26 percent of the bulls were considered unsatisfactory. Breeding to a subfertile or infected natural service sire will cause a significant delay in the interval to conception. In addition, it has been estimated that the cost per pregnancy of using a natural service bull is between $18 and $30 in feed cost alone.
Sire summaries, which provide accurate production, type, and calving ease information, are available. By using AI sires, dairy producers can use semen from several sires to minimize the risk of obtaining progeny from one low genetic merit sire (whether from a natural service sire or an AI sire whose genetic evaluation declined as more information became available). Also, breeding dates are more likely to be recorded, and calving dates more accurately predicted. In a pasture-breeding situation, heifers with reproductive problems are not identified until considerable time is lost. These heifers would probably not calve at the optimum age of 24 months, resulting in lost profits. Finally, the danger associated with maintaining a bull on the farm should not be ignored.
The major reasons dairy producers do not use AI for their heifers are the perception of lowered conception rates with AI, difficulty or time involved with estrous detection, location of heifers was inconvenient, and lack of restraint facilities. (Table 1.)
Estrous synchronization programs have been used and are being refined to minimize time spent for estrous detection and to manage an AI program for heifers that are located some distance from the main dairy facility. Acceptable conception rates can be achieved with properly designed and implemented programs. For a relatively small investment in time and money, most heifer facilities can be upgraded and equipped to provide restraint and handling facilities for heifers. In addition to administering treatments for estrous synchronization and insemination, such facilities can also be used for vaccination, deworming, pregnancy examinations, and perhaps embryo transfer.
The take home message is that there are solutions to the major reasons dairy producers do not use AI for their heifers.
| Statement | % Agree |
| AI for heifers is not profitable. | 10 |
| Conception rates are lower with AI. | 45 |
| There are more calving problems with AI. | 20 |
| Heat detection takes too much time. | 57 |
| Estrus is difficult to detect. | 33 |
| Synchronization is not profitable. | 20 |
| Synchronization requires too much labor. | 27 |
| The location of the heifers is inconvenient. | 79 |
| Lack restraint facilities | 80 |
| (Sulaiman, F., 1992, Penn State) | |
Research during the last decade has provided new information about changes in growth and degeneration of ovarian follicles during the estrous cycle. Using real-time ultrasound technology to monitor ovarian structures on a daily basis, several independent research groups recently showed that cattle might develop two, three, or four groups of follicles during each estrous cycle. Usually, one follicle in each group becomes dominant, suppressing the growth of the other follicles within the group. Such groups of developing follicles are called waves of follicular growth. Thus various populations of small, medium, and large follicles are present on the ovary each day of the cycle.
This concept of follicular development might explain the variation seen in intervals from prostaglandin (PG) injection until the onset of heat. Several studies have shown that—even though cattle have a corpus luteum (CL) and are likely to respond to PG—there is considerable variation among cows and heifers in the interval to onset of heat and degree of synchrony of heat when PG is administered. Since there are several waves of growth and degeneration of follicles during the cycle, the response rate and time to onset of estrus following a single PG injection may well depend on the degree of synchrony of follicular development and CL regression. In addition, a single injection of PG is only effective when administered to heifers that are beyond day 5 of the cycle when the CL is responsive to PG. The two-injection PG program with a 14-day interval between injections was developed so that all cycling heifers will be within the stage of the cycle when they will be responsive to PG on day 14 after the initial PG injection. The percentage of heifers responding will be significantly increased.
Secondly, since the target tissue for PG is the corpus luteum, PG will not be effective when used on peripubertal heifers. These heifers have not initiated estrous cycles and do not possess a CL. This is another major limitation of PG synchronization programs.
Various progesterone products used in conjunction with PG have been effective in synchronizing ovulation and estrus. Progesterone treatment before PG ensures CL regression in response to PG because all cycling heifers should have a CL that developed during treatment.
Progesterone will also delay estrus in heifers that undergo natural CL regression during the progesterone treatment period before the injection of PG.
Melengestrol acetate (MGA), a synthetic progestogen, which is administered in the feed, and the controlled internal drugreleasing device (CIDR) which releases progesterone have been thoroughly researched and approved for use in dairy heifers and beef cattle. When used with PG, these progesterone systems induce better synchrony of estrus among heifers compared to PG programs. Secondly either of these methods has the advantage of inducing estrus in some peripubertal heifers.
The combination of visual observation and insemination based on standing to be mounted can be an effective method of breeding heifers. However, the efficiency and accuracy of estrous detection varies greatly among farms. In some situations, this becomes a labor intensive activity, and occasionally first services do not occur in a timely fashion, delaying the age at first calving.
Several systems using prostaglandin have been developed, and researchers, veterinarians, and producers have adapted programs to suit specific herd situations. In selecting a system, consideration should be given to the following factors:
Results of synchronization can be expressed several ways, including the number of animals induced into heat during a specified period of time (synchrony), conception, and pregnancy rate. Conception rate is the number of animals that conceived, divided by the number that were inseminated. Pregnancy rate refers to the number that conceived, divided by the number that were assigned to the synchronization program.
System 1. All eligible heifers are injected twice with PG, 14 days apart, and those heifers that express estrus after the second injection are inseminated. Although many of them will come into heat between 48 and 72 hours after the second injection, five to six days of careful observation may be required to observe all the heifers that responded to PG. This system requires frequent and conscientious heat detection.
System 2. Cattle are inseminated by appointment at a specified time after the second PG injection. The time will vary—it may be 72 or 80 hours post-injection—depending on the PG product used. Research has consistently shown that conception and pregnancy rates are higher when cattle are inseminated based upon standing heat versus appointment breeding. Heifers that are in heat as early as 24 to 54 hours after the second injection would not conceive with appointment insemination, but would likely conceive if inseminated twelve hours after the onset of estrus.
System 3. This program is a variation of System 1, in which all heifers detected in heat after the first PGF injection are inseminated, and only those animals not observed in heat are reinjected 14 days later and inseminated based on observed heat. The advantages are timely insemination and less PG compared to System 1. However, there are two three-day periods of heat detection.
A comparison of systems 1, 2, and 3 is presented in Table 2.
| Program | No. Heifers | % Pregnant |
| AI at estrus after 1st PGF | 766 | 65 |
| AI at estrus after 2nd PGF | 1025 | 61 |
| AI at 80 hrs after 2nd PGF | 945 | 39 |
| Fogwell et al., J. Dairy Science 69:1665. | ||
System 4. Another plan consists of inseminating at the time of detected heat and by appointment. Animals not inseminated following detected heat by 72 hours are inseminated by appointment. This approach combines the advantages of the systems already discussed. Cattle are inseminated at the optimum time when inseminated at heat, and they achieve high conception rates. Breeding the remaining animals at a fixed time (72 or 80 hours) ensures that those animals which will ovulate but not detected in heat still have a chance to conceive. Good pregnancy rates can be achieved.
However, if the percentage of cattle detected in heat during the first 72 hours is low, then it is advisable to continue to inseminate based on detected heat and not to inseminate by appointment. This avoids wasting semen on hiefers not cycling.
System 5. This system is designed for synchronization of large groups of heifers when heat detection is not practical, but where self-locking head gates or stanchions are available. All heifers eligible to be bred are injected with PG, and two days later the tailheads are marked with paint or chalk. On the morning of the third day, heifers with the markings rubbed-off are inseminated. Any heifer that was observed in standing heat that morning, but has markings that were not completely rubbed-off, was also inseminated. Proper heifer identification and diligent record keeping are essential with this method. Injections are administered in the neck region so that identification can be confirmed. Figure 1 describes the program and results of a field trial conducted in a large herd in the state of Washington (Van de Graff et al., 1993 JDS Suppl. 1).
Approximately 2,000 heifers were processed through the system, and 74 percent were inseminated artificially, of which 62 percent conceived. Thus, the overall pregnancy rate was 46 percent. The entire process can be repeated as new heifers become eligible for breeding and for heifers that were not inseminated during the first cycle through the system.
Between 100 and 200 heifers were processed through this program per week. Based on progesterone analysis of several hundred heifers on the day of insemination, there was only a 2.5 percent error rate in the heifers inseminated when progesterone levels were elevated. Furthermore, it should be noted that 16 percent of those heifers that were not inseminated had high estrogen and low blood progesterone levels on the morning of the third day and, and thus would likely be in estrus that evening or the morning of the following day. Restraining the heifers and examining tailheads again that evening may have resulted in more heifers being inseminated. The data confirmed the low error rate associated with this PG-heat detection aid, programmed breeding system. It can reduce the time spent for reproductive management to only a few days each month and can be used at a remote location where heifers cannot be watched intensely for estrous behavior.
Labor efficient restraint facilities such as selflocking head gates are essential to the success of such a program.
1. Progesterone-releasing intravaginal device + prostaglandin (PG)
One method of administering progesterone is the controlled internal drug-releasing device (CIDR). This device is inserted into the vagina for seven days and gradually releases progesterone, which is absorbed by the vaginal tissue. Prostaglandin is injected on day 6, the day before the insert is removed. Studies have shown that if heifers are watched closely for estrous behavior, 80-95% will be synchronized to exhibit heat within five days of insert removal. Most heats occur on days 2 and 3. For convenience, the injection of PG can be given on day 7 when the insert is removed. The degree of synchrony of heats among heifers will be less when PG is given on day 7 but generally conception rate for the heifers detected in heat and inseminated will be similar. Heat detection aids should be used to ensure a high percentage of heats is detected. Data in Table 3 summarizes studies that involved 260 dairy heifers from four sites across the U.S. comparing PG system to CIDR + PG system. There is better synchrony of estrus and overall pregnancy rate with the CIDR + PG system.
2. Melengestrol acetate (MGA) + prostaglandin (PG)
Melengestrol acetate is an orally active progestogen that was developed in 1962. Early studies feeding MGA for short- or long-term duration resulted either in poor synchrony of estrus or good estrous synchronization, but poor fertility. More recently, an MGA + PG system was developed. Melengestrol acetate is fed at a rate of 0.5 mg/hd/day for a 14-day period. The MGA is fed in a grain carrier and either topdressed or blended-in with larger quantities of feed. Consistent intake of MGA is critical. Heifers will exhibit heat beginning within 48 hours after withdrawal of MGA. However, since fertility is low, they should not be inseminated at this time. Heifers are injected with PG on either day 17 or 19 MGA withdrawal and then inseminated based on observed estrus which usually occurs between 2 and 5 days after PG. Although a small improvement in pregnancy rate has been reported with the 19 day interval, more heifers were in heat within 72 hours of PG injection.
| Item | PG | CIDR + PG |
| Synchronization Rate | 57% | 84% |
| Conception Rate | 65% | 54% |
| Pregnancy Rate | 37% | 45% |
| a Modified from Lucy et al. 2001 | ||
Although this is either a 31or 33-day program, the advantages of the MGA + PG system are the good estrous response, good fertility, ease of administration of hormones, and reasonable cost.
Considerations when using MGA (D.J.Kesler, 2003. Professional Animal Scientist 19:96):
The advantages of programs that utilize progesterone either CIDR or MGA are better synchrony of estrus among a group of heifers and induction of cycling in some prepuberal heifers. Heifers that fail to exhibit heat or conceive following the initial synchronization will likely return to heat in a synchronized manner 18 to 24 days later. Time should be devoted to observing for heats during this period of time.
There are several modifications of these standard programs. For more information regarding details of various synchronization programs refer to the Iowa State Beef Center.
It describes synchronization programs, provides a calendar for most programs and calculates costs based upon herd specific expenses.
Although artificial insemination of synchronized cows in the final step in a synchronization breeding program, it is critical to the success of the entire program. Breeding a group of cattle during the short period of time following estrous synchronization may present problems for the herd manager and AI technician. It is important that special consideration be given to proper semen handling and insemination techniques to ensure optimum conception rate.
To move the breeding phase of this program along efficiently, each person should be assigned a specific job and thoroughly instructed prior to the breeding. One individual should be responsible for thawing semen and preparing the inseminating gun. This relieves the AI technician of additional tasks, allowing concentration on proper AI technique. Additional people could move cattle to and from the breeding chute.
Make sure an adequate holding area is available where heifers can be assembled for treatment, heat detection, and breeding. This area should have a breeding chute or similar arrangement where animals can be treated and artificially bred safely and efficiently. If possible, the synchronized animals should be observed for heat following hormone treatment. This would require that the holding area be equipped with sufficient feed and watering facilities for approximately five days until all synchronized cows are bred. The breeding chute area should be covered to protect semen, supplies, records, and personnel from adverse weather.
Since nearly 70% of Pennsylvania dairy producers use artificial insemination for heifers, this practice must be viewed as a profitable component of the dairy enterprise. AI provides genetic advancement within the herd (i.e., conformation and milk production), ensures monitoring of semen quality and fertility of AI bulls, eliminates the spread of veneral disease, provides farmers with information on calving ease to reduce problems with dystocia, provides a merchandising advantage for AI-sired heifers, and offers better control of the time when heifers calve. The major reasons for not using AI for heifers were the perception of lowered conception rate for AI, time commitment for heat detection, heifers kept at an inconvenient location, and lack of restraint facilities.
Acceptable conception rates approaching 50 to 75 percent for heifers are frequently obtained with and without the use of synchronization.
If problems associated with daily estrous detection limit the use of AI, then serious consideration should be given to using a synchronization program. A variety of systems are available, one of which should suit a specific herd situation. To achieve success with a synchronization and AI program, a producer must commit to follow the procedures carefully and pay attention to detail. It should be noted that those heifers, which fail to conceive after the initial insemination, will tend to return to estrus in a synchronized pattern. As more information becomes available about the mechanisms controlling follicular development, more precise synchronization programs will be developed, but good results are being obtained with currently available systems.
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Michael O’Connor
Pennsylvania State University
Department of Dairy and Animal Science
