Anyone who has spent time breeding dairy cows over the years has seen the reproductive changes that have occurred. Cows no longer exhibit signs of heat like they did just a couple of decades ago.

Especially in the larger dairies, timed A.I. has helped to improve heat detection rates, but conception rates have usually been less than desirable. Compliance is always something that needs to be investigated when working up poor conception rates to timed A.I. However, even when all aspects are performed precisely, conception rates to timed A.I. can still be lower than expected. So what might be happening? There have been many studies showing cows respond differently to these programs depending on where they are in their estrus cycle. Have you ever wondered why many dairies give two prostaglandin injections prior to first service timed A.I.? You might think it is to clean the uterus, and it does do that, but its main purpose is to have the majority of the cows between days five and 12 of their estrus cycle, which is the optimum time shown to start an Ovsynch program.

Currently in the western U.S. dairy industry, a large percentage of cows found “open” at pregnancy diagnosis are immediately started on a synchronization program or in some cases the program is initiated a week prior to pregnancy diagnosis (because GnRH has not been shown to affect pregnancy), and upon being diagnosed “open” are then given prostaglandin and continued in the synchronization program. Both of these strategies initiate synchronization programs regardless of where the cow is within her estrus cycle, and many cows fail to respond.

How can we get more cows to synchronize correctly to timed A.I. programs? Ultrasound can be a powerful tool in helping to accomplish this goal. It has the advantage over rectal palpation in being able to completely assess ovarian structures and better predict when cows fall into this “optimum” period to initiate or continue in these synchronization programs. Most important in predicting where a cow is within her estrus cycle is identifying the presence of an active corpus luteum (CL), which produces progesterone on the ovary. Ultrasound has been found to be far superior to rectal palpation in predicting an active CL. By using ultrasound, cows can be assessed and synchronization programs can be modified when cows fail to respond.

So how do you incorporate ultrasound into your timed A.I. reproductive management? For those that check their cows every week it can be as basic as looking for the presence of a CL at initiation of the timed A.I. program (first GnRH). Then scan a week later on the day of prostaglandin. If the cow has a CL, proceed with injection of prostaglandin and continue to breeding. If the cow had a CL the week prior and now has no CL, just restart the timed A.I. program by giving GnRH again. Most times these cows are cycling but are just around an estrus event, and a week later they will have a good CL and be ready to receive prostaglandin and proceed to breeding. However, there are a percentage of cows that are in nutritional anestrus or have persistent follicular cysts. These cows will fail to respond to the first shot of GnRH and have no CL two weeks in a row. Studies have found these cows respond better to the progesterone provided by the CIDR, and so starting them on a CIDR-synch program (basically an Ovsynch with a CIDR) will improve conception rates dramatically. Identifying and applying CIDRs only to cows that are most in need of supplemental progesterone can help to maximize conception rates and at the same time limit the cost of pregnancy.

Combining this management tool ultrasound provides with a synchronization program can be a powerful tool to maximize not only heat detection rates but also conception rates, which combine to improve overall pregnancy rates. Adding just one additional scan a week after the first GnRH and placing CIDR’s or restarting cows that lack a CL will greatly improve a herd’s synchrony within these timed A.I. programs, leading to higher conception rates, lower costs and, most importantly, more pregnancies. PD

Kevin McSweeney
Veterinarian
Bovine Reproductive Specialists, LLC
kmcsween@colostate.edu