Building a synch program can in bull-in breeding has advantages 

Though estrus synchronization programs are thought to be utilized primarily in AI operations, research indicates there are benefits to implementing a synchronization protocol in a bull-bred herd. Producers using natural service in their operations can reap many of the same advantages synchronization offers in AI operations. “In terms of the use of synchronization with natural service, I would say it is really underutilized because we often just don’t think about how effective that can be unless we are trying to accomplish an AI program,” Jordan Thomas, Ph.D., assistant professor and state beef reproduction specialist with the University of Missouri, said.

Benefits to Synch with Natural Cover

Regardless of the type of operation, a synchronization program can help producers accomplish the goal of getting as many females as possible bred early in their breeding season. This ensures producers have most of their females calving early in their calving season.  

When a female conceives earlier in the breeding season and subsequently calves earlier in the calving season, this accomplishes two important results. “The first thing that it does is it means that her calf is going to be older and heavier at the time of weaning next year. And that’s a big deal,” Jordan Thomas, Ph.D., assistant professor and state beef reproduction specialist with the University of Missouri, explained.

  An older, heavier calf translates into more dollars at weaning. “A modern beef calf will often gain about 2 pounds a day from birth to weaning and so if we are moving females up 20 to 40 days in terms of when they conceive, we can realistically be talking about 40 to 80 pounds that is not associated with genetic merit but is just associated with the age of the calf,” Thomas explained. 

The second beneficial result to a female calving earlier within the calving season is it gives her more time to recuperate before the start of the breeding season the next year. “So actually, from a probability perspective it changes her likelihood of conceiving early next year, which again is economically favorable,” Thomas added. 

The same is true in reverse for a female that conceives later in the breeding season and therefore calves later in the calving season. Her calf will be younger and likely weigh less at weaning. Additionally, she will have less time to resume a normal estrus cycle before breeding season begins again. Lastly, the narrower of a calving window an operation has, the more uniform the calves will be at weaning. 

Synchronization Protocols with Natural Cover

The synchronization protocol a producer chooses to implement depends on the length of the operation’s calving window. A producer with a well-managed herd with a calving season in the 45-day range may choose to utilize a different protocol than a producer with a herd that is calving within a 90-day window. 

Protocols range from one shot of prostaglandin to treatment with a CIDR for seven or 14 days. 

The protocols for producers implementing synchronization with natural cover slightly differ from protocols used in AI programs. The protocols are designed to keep from overwhelming the bulls with too many females in heat at the same time. “These programs are designed to spread out heat activity over the course of several days but still generate a pretty tight window so that we can generate that service opportunity early,” Thomas said. 

Producers will need to keep in mind the importance of having the appropriate number of bulls to service the herd. Producers should consult with their veterinarians to determine the protocol that is right for their operation. 

If producers are interested in seeing a group of calves born with an estrus synchronization and natural cover program, the Wudack Extension and Education Center near Cook Station, Mo., has calves on the ground from such a program. The center will hold a field day this fall for producers interested in checking out the calves and other programs. 

In addition, the MU Extension has detailed information on its website regarding specific estrus synchronization protocols to use with natural service breeding as well as recommendations on female to bull ratios at


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