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Estrous synchronization can add value

John Hall for Progressive Cattleman Published on 25 March 2019

Having a majority of cows in a cow-calf operation calve in the first 30 days of the calving season is critical to profitability for ranchers. A major opportunity for enhancing profitability is in moving late-calving cows forward to calve earlier in the calving season.

In an analysis of high-production/high-profitability herds, the researcher observed that in these herds, cows delivered over 60 percent of calves by day 21 of the calving season and 85 percent of calves by day 42. In addition, most of these herds maintained a 60- to 70-day breeding season.

Synchronization and calving distribution

Estrous synchronization can facilitate moving a higher percentage of cows to calving early in the calving season and maintaining a tight calving season. Studies from Missouri using commercial Angus cows (Figure 1) and Florida using tropically adapted crossbred cows (Figure 2) illustrate replacing natural service with combination of timed A.I. and estrous synchronization resulted in a greater percentage of cows calving in the first 21 to 30 days.

Effect of combination of estrus synchronization and A.I. calving distribution

Cumulative calving by year for two years

In both projects, cows bred by timed A.I. were exposed to clean-up bulls. In the commercial Angus herd, the percentage of cows calving in the first 21 days increased by 20 percent. For the tropically adapted crossbred cows, the percentage of cows calving in the first 60 days increased from approximately 20 to 80 percent.

Synchronization for A.I. or natural service

Synchronization technology has been available in various forms for over 40 years. However, systems that include controlled internal drug release devices (CIDRs) are advantageous since these systems induce cycles in non-cycling cows and heifers. There are several recommended estrous synchronization systems for cows and heifers. The seven-day Cosynch + CIDR and five-day Cosynch + CIDR protocols are recommended for fixed-time A.I. in cows. The 14-day CIDR-PG, MGA-PG and seven-day Cosynch + CIDR are the three most commonly used protocols for heifers.

It is extremely important for ranchers to fully understand estrous synchronization protocols and follow them exactly. For details on systems for use with A.I., ranchers are encouraged to consult the Applied Reproductive Strategies in Beef Cattle website or an A.I. company sire catalog.

A very good resource is the Estrus Synchronization Planner which allows ranchers to compare costs of protocols and generate calendars with specific directions on timing of synchronization drug injection, CIDR insertion and removal, and time of A.I.

Estrous synchronization can improve calving distribution when used with natural service as well. Common programs for cows or heifers are one-shot PG, four-day PG and CIDR for seven days. Last spring, Kalyn Waters covered these systems for Progressive Cattleman (Synchronization of estrus for natural service breeding programs). Another program for use in heifers is feeding MGA for seven to 10 days. In synchronized natural service situations, the female-to-bull ratio should be 20-to-1.

Researchers from the University of Kentucky have examined using synchronization for heifers and cows. Extension specialists worked with 601 heifers in 12 herds. Heifers were fed MGA for 14 days, then bulls were turned in 13 days after the last MGA feeding. This method resulted in 69 percent of the heifers pregnant to the synchronized estrus and 83 percent of heifers were pregnant within the first 30 days of the breeding season.

In cows, using a CIDR for seven days before bull introduction increased by 34 percent the number of cows pregnant in the first 30 days of the breeding season compared to no synchronization (Table 1). Even season-long pregnancy rate was improved by 8 percent in the cows that received synchronization.

Effect of estrus synchronization prior to natural service

Risks and rewards

It is clear using estrous synchronization with A.I. or natural service can increase the percentage of calves born early in the season. Before adopting any technology, ranchers need to appreciate the risks and rewards to the operation. Estrous synchronization is no exception. The first question ranchers ask is, “Won’t calves all come on the same day?” The natural variation in gestation length between cows means cows all bred on the same day will calve over a two-week period.

For example, at the University of Idaho Nancy M. Cummings Center, we A.I. 300 cows on a single day. Our fixed-timed A.I. pregnancy rate has ranged from 55 percent to 65 percent over the last 10 years. On average, we will calve 180 to 185 cows to A.I. The sire also influences the gestation length of calves. In 2017, we bred cows to six different bulls, so the cows that conceived to A.I. calved over a 20-day period. Calving data from 2018 illustrates the pattern of births we see (Figure 3).

2018 calving distribution of 172 calves born to cows bred by fixed-time A.I.

We calve in late February for a variety of research and teaching reasons. Cows calve on pasture with straw available for bedding. There is a calving barn and maternity barn available if we need to bring cows in during bad weather.

While we run the risk of calving during a stretch of bad weather since we calve above the 45th parallel in late winter, our calf losses during the A.I. calving are very low and similar to the cows bred to clean-up bulls. The tight calving window allows us to focus our energy on observing cows and helping calves as needed. We feel we give better attention to the few cows that need assistance (malpresentations) or calves that may need some attention.

Admittedly, the location of the UI Nancy M. Cummings Center is dry and has limited wind by Western standards. Shifting our calving time would reduce our stress during calving time, but we continue to use this timing for research purposes. Ranchers can mitigate the risk associated with calving a high percentage of cows in a short time by having proper facilities, sufficient labor and adjusting calving season.

The next question asked is “Will it pay?” Depending on the synchronization system used, the cost of estrous synchronization drugs can vary from as little as $2 per cow to $20 per cow. Labor to gather cows and put them through the chute needs to be added into the cost. Remember Figure 2, where the Florida group moved cows from a 120-day calving season to a 70-day calving season by changing from natural service to a combination of timed A.I. and natural service?

They also calculated the increase in value from that change in management (Table 2). In the first year, they increased the average age at weaning by almost 22 days by having more calves born early in the calving season.

Breeding season length and change in calf age and value after incorporating estrus synchronization

This resulted in an increase of 44 pounds of weaning weight per calf.

Using the five-year average of $2 per pound for five-weight steers, gross calf value was increased by $87 per calf. This would result in a $26,000 increase in gross income for a 300-cow herd. After six years, the average age of calves at weaning had increased by 42 days compared to before synchronization and A.I. The increase in age (and resulting weight) was calculated to increase calf value by $169 per calf and increase gross ranch income by $50,700.


Incorporation of estrous synchronization into breeding management strategies for cow-calf operations can result in benefits to calving distribution and ranch profitability. Ranchers can use this technology for programs using natural service or A.I. followed by natural service. If you are interested in using an estrous synchronization program, consult your state extension beef specialist or veterinarian.  end mark

John Hall
  • John Hall

  • Extension Beef Specialist
  • University of Idaho
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