According to the Dairy Cattle Reproduction Council, a focused effort on reproductive management can increase pregnancy rates. There are several reproductive programs available, so keep your dairy’s individual management style in mind when evaluating the options.
The following questions (and answers) can help ensure your dairy’s reproductive program is complete.
Are pre-synchronization programs before Ovsynch important?
Absolutely! The timing of ovulation synchronization, or Ovsynch, is fundamental because it will determine the likelihood of ovulation to the first GnRH injection and ultimately the synchronization of the estrous cycle.
Studies have shown that when beginning the Ovsynch protocol between day five and nine of the estrous cycle, there was significant improvement in the percentage of cows that ovulated.
Is pre-synchronization important for both first timed A.I. and resynchronization?
Yes. Several studies have shown that using a pre-synchronization program before resynchronization can increase pregnancy per insemination by approximately 5% to 10%. Using GnRH seven days before Ovsynch or using prostaglandin (PG) seven to 11 days before Ovsynch can improve fertility compared to no pre-synchronization method.
Studies have shown when heat detection is utilized the interval between inseminations is reduced for PG-based pre-synchronization programs. This is due to a large number of cows getting removed from a synchronization program because they were detected in heat and bred instead of going all the way through the synchronization schedule.
Is a GnRH- or PG-based pre-synchronization program best for my dairy?
The option you choose depends on the goal of your dairy. If you can accurately and efficiently detect when a cow is in heat and you can achieve similar or higher fertility than a full timed-A.I. program with no heat detection, then take advantage of this cost-effective opportunity. If this method works for your dairy, avoid synchronization programs that reduce the ability to detect when cows are in heat. These protocols use multiple GnRH injections, which suppress heat detection.
However, using protocols such as Presynch (two shots of PG 14 days apart, 10 to 14 days prior to Ovsynch for first timed A.I.) or a modified Presynch (one shot of PG seven to 14 days prior to Ovsynch for a resynchronization program) can promote heat detection due to using PG. Therefore, if heat detection is one of your goals, a PG-based protocol should be the preferred synchronization program.
Another option to consider when deciding between GnRH- or PG-based resynchronization programs is whether or not your team members can accurately identify non-pregnant animals and determine if ovarian structures are present. Farms using ultrasound to diagnose non-pregnant cows and determine if there is a corpus luteum (CL) present should use a PG-based program.
The CL is a mass of cells in the ovary that is present when ovulation occurs. GnRH helps induce ovulation in cows without a CL, while PG is only effective in cows with a CL present.
Should cows be heat checked during a synchronization program?
If you can achieve similar or better pregnancy per insemination using heat detection with a timed-A.I. program, this is the most cost-effective way to get a cow pregnant. However, recent studies would suggest that very high fertility can be achieved by using a Double Ovsynch with two PG and timed A.I., so make sure you properly evaluate potential fertility to either heat detection or using a full timed A.I. with a robust synchronization program.
In some situations, however, facilities, management or staffing may not allow for heat detection. If that’s the case, then a full timed-A.I. program is the preferred method.
For example, footing on a farm can also be a factor. In facilities where cows are on concrete (i.e., freestalls), the number of cows detected in heat can be reduced, and fertility to those heats can be similar or lower than using a full timed-A.I. program. The opposite seems to be true when cows are on dirt, although a variety of factors such as milk production level can also play a factor.
Does the timing of a pregnancy diagnosis and starting resynchronization affect fertility?
Yes. The timing of when pregnancy is confirmed should be a consideration in what synchronization program is utilized. Researchers continue to explore ways to reduce the interval between inseminations to increase pregnancy rate and reduce open days.
Most dairies initiate their resynchronization program either prior to or at non-pregnancy diagnosis. The timing of pregnancy diagnosis and initiation of the synchronization program may reduce estrus expression depending on the timing and type of hormonal injection used. A recent study revealed if GnRH began 17 days after timed A.I. versus waiting until 24 days, heat detection was reduced by 25%. Also, as mentioned earlier, if GnRH is given at non-pregnancy diagnosis versus PG one week prior to beginning Ovsynch, heat detection is reduced by 50%.
When fine-tuning your reproductive protocol, always work with your veterinarian to evaluate and establish clear goals. 
PHOTO: Photo by Jenna Hurty.
-
Todd Bilby
- Associate Director
- Ruminant Technical Services
- Merck Animal Health
References omitted but are available upon request. Click here to email an editor.
Reproduction program considerations
- When implementing Ovsynch protocols, the estrous cycle should be pre-synchronized to assure a large percentage of cows are synchronized between day five and nine of the cycle.
- Pre-synchronization for timed A.I. and resynchronization programs will increase fertility and pregnancy rates. While pre-synchronization seems to increase the intervals between inseminations, the interval is actually reduced (in PG-based programs) because of more cows coming in heat and getting bred.
- GnRH-based protocols suppress heat detection, so PG-based protocols should be the preferred synchronization protocol if heat detection is a goal and if fertility is good for the cows detected in heat.
- Heat detection is the least expensive way to get a cow pregnant, so even if timed A.I. programs are in place, selecting cows that are seen in heat is recommended if you have good fertility to the heats.
- Complete timed A.I. programs (no heat detection) could be the preferred reproductive program in many circumstances as well as the goals of your farm. Remember that compliance plays a crucial role when no heat detection is used.
