It is still possible to maintain good reproductive performance in dairy herds without synchronization and timed A.I. (TAI), but it requires an effective systematic heat detection program that identifies approximately 70 percent of all possible heat periods.

Unfortunately, maintaining such a heat detection program and quality heat detection personnel can be a never-ending challenge in today’s expanding herds. As the accuracy and efficiency of heat detection declines in many herds, the value of incorporating synchronization and TAI into the management program increases proportionately.

Especially in large herds, it is almost impossible to visually examine every cow for estrus activity. Traditional methods of visual heat detection followed by A.I. do not work well when cows are managed in large groups. Large herds require more time for heat detection, identification, sorting, A.I. and record keeping – simply because there are more cows. The equal distribution of the onset of estrus during the day, combined with the average estrus period of seven mounts over a 7-hour duration, is a major reason why heat detection rates are usually less than 50 percent and also why TAI programs were developed – because visual heat detection was not getting the job done.

Today most large herds use tail-chalking as the primary method to determine who to A.I., with TAI employed as a safety net to inseminate cows not detected in estrus. Cows should be inseminated based on rubbed tail heads when the disappearance of chalk is validated with an additional secondary sign of estrus, such as vaginal mucous, ride marks, a red swollen vulva or a normal 18 to 24 estrous interval. Unfortunately, tail-chalking is part art and part science and may produce poor results if periodic evaluation and retraining are not conducted. The misidentification of estrus may be a problem if the breeder does not properly “read” the chalk, which may result in lower conception rates. Two important factors allow tail-chalking to work as a heat detection system: consistency in where cows are observed at the same time each day and that every cow is observed everyday. If expression of mounting activity is reduced, then chalking becomes less effective.

Almost 70 years elapsed between the first published recognition that female mammals display a predictable increase in physical activity when in estrus, and the first useful field application of pedometry. Cows in estrus were about four times as active as cows not in estrus when housed in a freestall barn. When cows were housed in bedded packs, cows in estrus were about 2.7 times more active than those not in estrus, indicating that type of housing influences the magnitude of physical activity change.


Milking equipment companies (AFI, BouMatic, DeLaval and WestfaliaSurge) have pedometer technology integrated with the milking system at various stages, either in the milking parlor with an alarm system or downloaded into a central computer for list report generation. Activity technology commercially available today has improved greatly since first being introduced 20-plus years ago. Activity systems compare each cow’s activity (steps when an ankle tag is employed and movement with a neck bracelet) since the last interrogation (usually the last milking) to a pre-set baseline time period (usually the previous 10 days). This allows for comparison of activity within an individual cow and thus increases the accuracy of the system.

Voluntary waiting period (VWP) and first service
Determining the best time to start breeding cows is a balancing act between attempting to achieve pregnancies efficiently and taking into consideration the other demands being placed on the cow. Traditionally, the VWP varies from 50 to 90 days in milk in most dairy herds. Duration of the VWP or start of the breeding period after calving is a management decision that should be set by the type of breeding program being used. When using visual signs, chalk rubs or pedometer activity as the method to determine which cow to A.I., the VWP should be between 50 and 70 days in milk. When using a TAI protocol such as either Ovsynch or Presynch + Ovsynch, the VWP should be at least 70 day in milk or longer, if the average body condition lost from calving to A.I. is greater than one body condition score. A rule of thumb when determining the VWP is: For every delay of an estrous cycle (21 days) in the VWP, the conception rate must increase 8 percent to obtain similar days open and proportion of cows pregnant at different intervals post-calving. For example, if the VWP for a dairy is 50 days, and the conception rate is 28 percent, delaying the VWP to 70 days in milk must result in an increased conception rate to 36 percent to maintain median days open.

Commonly used timed A.I. programs
The most accepted TAI protocols in dairy herds in the U.S. are the Ovsynch and Cosynch protocols, which consist of an injection of gonadotropin-releasing hormone (GnRH) given at random stages of the estrous cycle, followed seven days later by a prostaglandin (PGF). For Ovsynch, a second GnRH injection is given 48 hours after the PGF and TAI is performed 12 to 18 hours later. When Cosynch is utilized, cows receive TAI 48 or 72 hours after the PGF and GnRH is given concurrently. Approximately 10 to 15 percent of the cows display signs of estrus during the protocol, and they should be inseminated promptly.

Conception rates following the Ovsynch protocol are optimized when cows ovulate to the first GnRH injection of the protocol, and when a responsive corpus luteum is present at the moment of the PGF injection. Research at both the University of Florida and Kansas State University reported giving two injections of PGF 14 days apart; the second injection given 12 days prior to the first GnRH of the TAI protocol increased pregnancy rates because a higher percentage of cows were inseminated at an optimum stage of the estrous cycle. Because of the convenience of giving injections on the same day of the week, many producers have opted for the two injections of PGF 14 days apart and 14 days prior to initiation of the first GnRH of Ovsynch protocol.

Adjustments to protocols that should increase conception rates
Option I (see Figure 1*) is the first-service protocol most commonly used by producers today because of the convenience of giving the two Presynch PGF injections the same day of the week and the ease of having TAI and the second GnRH being at the same time, thus reducing one handling or locking-up of cows.

Option II (see Figure 2*) is a combination of both university studies and large field trials that have shown an increase in conception rates (approximately a six-unit increase) for pre-synchronizing using a 14-day interval between PGF injections and 12 days prior to Ovsynch to optimize stage of the estrous cycle prior to GnRH. Additionally, delaying the second GnRH injection of Ovsynch to 56 hours from 48 hours and TAI 16 hours later has shown an increase of approximately a seven-unit increase in first-service conception rates. The addition of these two adjustments may not be additive (you will probably not see a 13-unit increase in first-service conception rates), but they both optimize the biology of follicular development and ovulation of the ovum with the bonus of no extra costs, besides maybe labor expense to sort or lock-up cows differently.

Compliance as defined for a synchronization protocol is the administration of hormone injections to the correct cows at the correct time intervals. The more complicated a protocol, the greater the chances are for procedural failure. Protocol compliance is critical for success.

For example, the standard Presynch + Ovsynch protocol requires that each cow receive five hormone injections at appropriate days in milk and in the correct sequence. Failure to administer any one of these five hormones or administration in an incorrect sequence will result in a failure of the protocol to deliver an ovulated ova following insemination. If at each step a 95 percent compliance is achieved, the cumulative compliance becomes 77 percent, which should not be acceptable. When selecting a synchronization protocol, two factors determine the success of any program:

1. cycling cows in excellent body condition

2. compliance to the prescribed protocol.

Work with your veterinarian or reproduction consultant to design a tailor-made program for your dairy.

The value of a pregnancy
Economic value of a pregnancy is the difference in all expected future net returns from two identical cows, one pregnant and the other one open. A cow’s value changes over time and depends on her lactation number, level of milk production, days in milk and pregnancy status. To demonstrate the value of a pregnancy, Albert de Vries at the University of Florida compared two average second-lactation cows, assuming one cow is still open after 300 days in milk and the other cow becomes pregnant at 61 days in milk (one day after the VWP).

The value of the open cow decreases over time and at about 300 days in milk she gets near the point where replacing her becomes the more profitable decision. The economic value of the second cow who conceived at 61 days in milk actually decreases for awhile because she is still at risk for involuntary culling due to mastitis, death, lameness, etc. before the next calving. However, the value of the pregnancy increases with the length of the pregnancy because it becomes more likely that she will actually calve and have a third lactation. The value of the eight-month-old pregnancy at 300 days in milk compared to the open cow at 300 days in milk is $720.

Realistic economic benefits of improved reproductive performance are not simple to estimate. When reproductive performance improves, all changes in cash flows that result from the improvement must be accounted for. Cows that become pregnant faster (shorter calving intervals) will spend on average more time in early peak lactation and are at less risk to be culled for reproductive failure. But they will also have more days dry per year and are more often at risk for involuntary culling due to fresh cow problems, so it is somewhat of a balancing act.

You only get one chance for a first service. So based on your dairy’s programs, the transition program that will affect dry matter intake and subsequent body condition maintenance to heat detection programs using TAI, chalking of tail heads or an activity system, are you getting the most out of your first service program?

GnRH – Cystorelin®, Factrel®, Fertagyl®, and OvaCyst®

PGF – estroPLAN™, Estrumate®, In-Synch®, Lutalyse®, and ProstaMate®

Note: Times listed for TAI should be considered as the approximate average time of insemination. This should be based on the number of cows to inseminate, labor and facilities. PD

Dr. Ray Nebel
Senior Reproduction Specialist

*Figures omitted but are available upon request to