Estrus synchronization in beef cow herds offers numerous advantages, including shorter calving seasons, more uniform calf weights, and enhanced genetic selection through artificial insemination (AI). With rising bull costs and efforts to improve herd genetics, many producers are turning to estrus synchronization. This guide outlines key considerations for successfully implementing synchronization systems.
Key Actions for Implementing Estrus Synchronization
- Select an Appropriate Synchronization Protocol:
- Review various estrus synchronization programs available through the Beef Reproduction Task Force website. Use tools like the AI Cowculator app to evaluate the economic viability of different protocols based on your operational constraints, including manpower, facilities, and budget.
- Plan for Timely Treatment:
- If opting for protocols that require advance preparation (e.g., MGA for heifers), start treatment about 40 days prior to the breeding date. Ensure that all necessary supplies are ordered and delivered on time to avoid delays in the synchronization process.
- Determine Breeding Method:
- Decide whether to conduct AI or utilize natural service for breeding. If lacking AI skills, consider hiring a professional technician who can manage the AI process effectively. Following synchronization protocols precisely is crucial to achieve optimal pregnancy rates.
- Calculate Bull-to-Cow Ratios:
- If using natural service after AI, maintain a bull-to-cow ratio similar to non-synchronized breeding (approximately 1 bull for every 20 cows). If AI is successful, estimate needing about half the normal bull count for clean-up breeding, as non-pregnant cows will return to heat over several days.
- Conduct Pre-Breeding Evaluations:
- Schedule bull breeding soundness exams 1-2 months before the breeding season to assess the health and fertility of bulls. This exam should evaluate not just semen quality but also physical soundness, including feet, legs, and reproductive anatomy.
Effective estrus synchronization can significantly enhance the productivity and profitability of beef operations. By carefully selecting protocols, planning treatments, determining appropriate breeding methods, calculating bull ratios, and ensuring bull soundness, producers can optimize their breeding programs for better outcomes. As breeding season approaches, it's essential for producers to assess the potential benefits of synchronization for their herds.
FAQ: Artificial insemination (AI) & Estrus synchronization for cattle
What would be a good bull to heifer ratio and how much is bull overload possible, or is natural service not even recommended when using the MGA/prostaglandin synchronization method on my heifers?
You can use natural mating with estrous synchronization with the MGA/prostaglandin (PG). Bulls need to go through a breeding soundness evaluation. I would suggest a minimum scrotal circumference 34 cm for yearling bulls. In the experiment that we conducted, we had 40 synchronized heifer using MGA/PG and 4 yearling bulls. We put two bulls in with the heifers at one time. For the first 4 days post PG injection, bulls were rotated every 12 hours and days 5?7 post PG injection, bulls were rotated every 24 hours.
The injection of PG tightens the synchrony and you might expect the majority of the females that respond to exhibit heat 40 to 72 hours post PG. If you do not give the injection of PG the degree of synchrony will be less and cows will come into heat over a longer period of time.
Remember, the first heat post MGA feeding is not fertile.
-Dr. Rick Rasby, Professor of Animal Science
What are some benefits of artificial insemination in beef cows?
Artificial insemination of beef cows or heifers allows you access to genetics that you may not have the opportunity to purchase and use via natural service. You would have access to genetics of a number of different breeds that may compliment the breed make-up of your herd. Many times estrous synchronization and artificial are used together and this can be used to reduce the length of the calving season and calves have the potential to be more uniform at weaning. When using artificial insemination, you will need to have the facilities and labor to accomplish this management practice.
How do semen and embryos stay alive while frozen and then come back still alive after thawing?
The ability to cryopreserve germplasm banks of frozen embryos indefinitely allows genetic diversity to be preserved. This process allows freezing and thawing without death. Cattle embryos can be successfully frozen and stored indefinitely at -196°C in liquid nitrogen. Cryopreservation is a multistage process incorporating a cryoprotectant or antifreeze and the thawing and transfer of embryos is carried out in a manner similar to frozen-thawed semen. Following freezing and thawing pregnancy rates of up to 45% to 50% are currently achievable.
In contrast to embryos, oocytes (eggs) are extremely sensitive to chilling and are difficult to cryopreserve. The development of new cooling technologies using liquid nitrogen (LN2) cooled below -196°C (LN2 slush), however, have enabled the efficient cryopreservation of oocytes. There is research in cryopreservation of ovarian tissue that researchers say will become a reality enabling the preservation of pure genetic stocks of female as well as male gametes.
How long or how many years will semen last in a semen tank if conditions are perfect?
I'm not sure I know the answer, but if the tank is monitored closely and is kept charged with nitrogen, the semen can be stored for long periods of time. I know the Meat Animal Research Center in Clay Center, NE has germ plasma evaluation experiments and they have semen from bulls as far back as the 1970s.
Is there any reason that heifers cannot be fed MGA for 14 days then take them off, let them cycle once, then breed them on the next cycle? My thinking is that they will be grouped within 3 to 4 days, which I could live with.
MGA is approved to inhibit estrous cycles in beef cattle and is the reason why it is used in estrous synchronization protocols. You can feed it for 14 days and not use the prostaglandin injection that is usually given 17 to 19 days after feeding the MGA. DO NOT breed the heifers that come into estrus right after feeding MGA. This estrus is not very fertile. I don't think the protocol without the injection of prostaglandin will make the synchrony of estrus as tight as what you indicated, 3 to 4 days. I think those that respond, the synchrony of estrus will be more like 7 to 9 days during the second heat period after MGA.
Where is the best site for IM injections for estrous synchronization while in a BQA program?
Follow BQA guidelines and label direction on the product being used. Because the product is an intramuscular injection, inject into a muscle in front of the shoulder (neck) using a 1.5 inch 18 gauge needle. I would suggest a 1.5 inch needle compared to a 1 inch needle, especially for cows to make sure the product is delivered into the muscle.
Can annual synchronization of females cause fertility problems in beef cows?
Synchronizing estrus in cows and heifers is an effective way to maximize the use of time and labor required to detect standing estrus in cattle. In addition, by using estrous synchronization more cows can potentially conceive and become pregnant early in the breeding season with no decrease in fertility.
Some estrous synchronization protocols can even induce estrous cycles and shorten the anestrous postpartum period allowing cows to conceive earlier in the breeding season. Because some estrous synchronization protocols can induce estrus in non-cycling beef females, this is not a replacement for good nutritional management practices. The females that are most likely to be induced to come into estrus are those that are already close to cycling.
However, when estrous synchronization is used together with artificial insemination, one of the largest factors that influence fertility is efficiency and accuracy of estrous detection.
When fertility is defined as the percentage of cows that conceive in the first few days of the breeding season, synchronized cows will have increased fertility compared to non-synchronized cows.
When fertility is defined as the percentage of cows that conceive during the first cycle (first 21 to 25 days) of the breeding season, estrous synchronized females will have similar or better fertility than non-synchronized females depending on the percent of animals that are anestrous or prepubertal and the synchronization protocol used.
Therefore, estrous synchronization can be a tremendous management tool to get more cows pregnant early in the breeding season.
Drugs used in these programs are naturally occurring in the animal.
How many clean-up bulls are needed after estrus synchronization and artificial insemination (AI)?
The following article is a summary of the article reviewing scientific literature evaluating bull:female ratios following estrus synchronization and artificial insemination (AI) found in the 2016 Nebraska Beef Cattle Report.
One of the benefits of estrus synchronization and AI is purchasing and maintaining fewer bulls. However, an idea has been circulating that synchronized females not becoming pregnant to AI will return to estrus at the same time and require the same number of bulls as natural service without AI.
Research has indicated cows not conceiving to AI will return to estrus over a 12d period following a single timed AI. The most active day had 18 percent of the herd in estrus, with the remainder of the distribution a bell curve (Figure 1 below). Each cow’s estrous cycle is slightly different. Some cows have 2 follicular waves during the estrous cycle, while others have 3. This results in a natural variation in cycle length, causing the non-pregnant cows’ return to estrus to vary.
There will be three or four days when many of the non-pregnant females will be in estrus. On those days it is important to increase observation of bulls, especially in large or multi-windmill pastures, to ensure they are all sound and working.
No effect of bull to female ratio or number of females expressing estrus per bull on pregnancy rate was found when comparing bull to heifer ratios ranging from 1:7 to 1:51 in heifers synchronized with Synchro-Mate B. In a comparison of bull to heifer ratios ranging from 1:16 to 1:50 in herds of 100 heifers synchronized with melengestrol acetate (MGA)-PG and immediately exposed to bulls, the optimal bull to heifer ratio for synchronized heifers was 1:25 based on both biological and economic criteria. If the optimal bull to heifer ratio in a synchronized natural service setting is 1:25, it can be extrapolated with a hypothetical AI pregnancy rate of 50 percent, the number of clean- up bulls needed is decreased by 50 percent.
Data was summarized from published studies reporting AI and final pregnancy rates, and bull to female ratio. Of the data collected, studies were divided into bull to female ratio groups including Normal-Natural Service (NS, 1:20 to 30 bull to female ratio), and 3 groups following estrus synchronization and AI:
- normal (NORM, 1:20 to 30),
- intermediate (INT, 1:31 to 49), and
- half (HALF, 1:50 to 60).
The final pregnancy rate of a normal bull to heifer ratio in a natural service setting was 87.8 percent. Final pregnancy rate in the NORM was 87.7 percent. The final pregnancy rate in the INT group was 82.6 percent and the final pregnancy rate of the HALF was 89.2 percent. Bulls turned in at half the normal bull to female ratio following estrus synchronization and AI resulted in final pregnancy rates similar to normal bull to female ratio both in a natural service situation and following estrus synchronization and AI.
A consideration to make prior to choosing a bull to female ratio is bull age. Experienced bulls are more efficient breeders, while yearling bulls are less experienced.
Another consideration is pasture size and terrain; a rugged, multi-windmill pasture may demand more from a bull than a flat single-windmill pasture.
Conclusion
In conclusion, producers utilizing estrus synchronization and AI should keep in mind the similarity between final pregnancy rates when using a 1:25 bull to female ratio and 1:50 bull to female ratio. Producers need to evaluate the cost difference of purchasing and maintaining twice as many bulls to maintain a 1:25 bull to female ratio following estrus synchronization and AI.
Rick Funston, reproductive physiologist, purchases 100 heifer calves every fall for the West Central Research and Extension Center and AI in the spring. He has never used more than half the normal number of bulls that is recommended without AI and has consistently reported over 90 percent final pregnancy rates in a 60d clean-up breeding season. This includes more than 1,200 heifers to date.
Full report: How Many Clean-up Bulls Are Needed After Estrus Synchronization and AI?
-Rick Funston, Ph.D., University of Nebraska — Lincoln, Professor, Beef Cattle Reproduction Physiologist
-Hazy Nielson, Nielson Reproductive Service, Ellsworth, NE
