The major factor limiting optimum reproductive performance on many dairy farms is failure to detect cows in heat in a timely and accurate manner. Poor heat detection results in excessive number of days not pregnant (days open) which causes long calving intervals. This is economically important to the dairy business because for every day a cow is not pregnant beyond 120 days after calving it costs about $3.00 per cow per day. For a 250 cow herd with an average of 140 days open, the cost would be at least $60 per cow or $15,000 per year compared to 120 days open.
There are several systems available to dairy producers to help improve heat detection rate or the number of cows submitted for breeding at the proper number of days after calving. Some systems termed estrous synchronization programs are designed to cause cows to come into heat over a short period of time so they can be inseminated in a timely manner. Heat detection is required for these programs. The newer systems, termed timed breeding or appointment breeding, are designed so both the onset of heat (estrus) and ovulation are induced so cows can be inseminated at a specific time without heat detection. Depending upon the specific system, the potential benefits of such programs include the following.
Advantages of systematic breeding programs
- Improve the efficiency of heat detection
- Achieve more timely first service
- By improving the 21-day pregnancy rate there will be a reduction in the variation in calving intervals among cows
- Possibly reduce involuntary culling for reproductive reasons
- Concentrate labor for reproductive management to specific time periods
- Improve the overall reproductive performance of the herd
Hormones Used To Synchronize Heat And Induce Ovulation
Reproduction is naturally controlled by hormones. In order to synchronize a group of cows or heifers into heat and induce ovulation, hormones have to be administered at specific times following a standardized system. Failure to follow the details of these systems will cause poor results. The major hormones used in synchronization programs and the function of each are listed below.
- Prostaglandin - PG: most synchronization methods use one or more injections of prostaglandin. Toward the end of the estrous cycle the cow naturally produces PG to regress the corpus luteum (CL) which has been producing progesterone during the middle of the estrous cycle. When this occurs the dominant follicle is allowed to complete development, produce estrogen, cows come into heat and ovulate. If PG is injected at the correct stage of the cycle the same sequence of events will occur.
- Gonadotropin Releasing Hormone - GnRH: is produced naturally in the brain and causes release of other hormones which are important for follicular development and ovulation. When injected into cattle, GnRH causes either ovulation of the dominant follicle or formation of luteal tissue within the follicle which will regress when PG is injected later.
- Progesterone - P: is the hormone produced in high levels by the CL between day 5 and 16 of the estrous cycle. The hormone prevents heat and ovulation. If the cow is pregnant, progesterone maintains pregnancy. When used in heat synchronization programs, progesterone is released slowly from a device that was inserted into the vagina for five or seven days. This progesterone treatment before an injection of PG ensures regression of the CL in response to a PG injection because most cattle will have a CL that has developed over the seven day period. Progesterone will also delay heat in cattle that undergo natural regression of the CL during the five or seven day period before a PG injection.
Commercial Hormone Products
Here is the list of commercial products available for use in synchronization of cattle. Ask your veterinarian about additional products as they become available.
- CIDR insert device
- MGA - progestogen in feed
Estrous Synchronization Programs
There are several systems used for synchronizing estrus. These systems may require one or more of these hormones. Each system has a specific schedule of hormone treatment and dosage. The following is a list of general synchronization programs and the hormones used. Consult your veterinarian for specific protocols.
- Standard prostaglandin program - PG injections
- Ovsynch program - PG and GnRH
- Presynch program - PG prior to standard Ovsynch program
- G6G - GnRH injection 6 days prior to standard Ovsynch program
- Double Ovsynch - two rounds of GnRH and PG prior to timed insemination
- Controlled internal drug releasing device (CIDR) - vaginal insert of prosgesterone with a PG injection the day before or the day of insert removal.
- Melengesterol acetate (MGA) - progestogen product administered in feed followed by PG injection. This system is used primarily for beef cows and heifers. It is not appropriate for lactating dairy cows.
Example of an estrous synchronization program
This is the Presynch-Ovsynch program which is a typical program for dairy herds
Factors important to achieving success with synchronization programs:
- A high percentage of the cows must be cycling normally. Nutritional, environmental, or disease factors that prevent cows from cycling (anestrus) or cause low conception must be corrected before starting a synchronization program.
- Although the Presynch and Ovsynch programs will induce some anestrous cows to ovulate, pregnancy rates will significantly increase in relation to the percentage of cows that are cycling at the onset of the program.
- Pregnancy rates are significantly higher for cows with Body Condition Scores (BCS) > 2.5 compared to cows with BCS < 2.5
- Herd managers and employees must make a commitment to the synchronization program.
- Accurate records must be kept. A list of eligible cows must be updated regularly. A calendar or electronic record system should be used so injections, heat detection and inseminations are performed on the correct days specified for the system. Appropriate personnel should be available to perform these tasks correctly. Standard operating procedures (SOP) should be posted and understood by everyone.
- Efficient and accurate heat detection for the specified days is essential when using the synchronization programs that require heat detection. Heat detection must be intensified on the days when cows are likely to exhibit heat. Use of heat detection aids is recommended.
- To maximize the effectiveness of any system, post breeding heat detection (detection or return heats) must be high.
- Herd managers and employees must adhere to the time schedule for injections, heat detection, insemination and pregnancy examinations.
- The proper amount of hormone must be given in the correct location.
- Use the correct weapon on the correct target - when administering a hormone use he proper dose and syringe and needle size. GnRH and PG should be injected into the muscle, so use the appropriate size needle for the area where the muscle is located. Review these procedures with your veterinarian. Keep hormones refrigerated.
- Pregnancy examinations must be scheduled routinely so non pregnant cows are identified and scheduled back into the synchronization program.
- When the timed insemination occurs shortly after day 70 postpartum, pregnancy rates are higher compared to when the timed insemination occurs before day 70 postpartum.
Successful reproductive management depends upon team work. Herd managers should consult with the veterinarian, artificial insemination personnel and employees so everyone is working toward the same objective. It is critical the herd manager consult with the veterinarian in selecting the best systematic breeding program and protocols.
Prepared by Michael L. O'Connor, Professor of Dairy Science