In 1986 Dr. Freeman, dairy breeding research scientist from Iowa State, stated in a research article that “continued successful selection for production may depress reproduction to where selection on reproduction may be necessary,” and then asked, “Will reproductive physiologists develop new techniques to enhance reproductive performance so that selection will not be necessary?” More recently two trends have occurred.

There has been a rapid adoption of estrous synchronization or timed insemination programs, and genetic traits for cow fertility have been incorporated into selection indexes. Sire Conception Rate became available in August 2008. In a survey of large herds across the country, Caraviello et. al. reported that 87 percent of the herds used estrous synchronization or timed A.I. programs.

Furthermore it was documented by Goodling et.al. that herds using synchronization protocols had 17 fewer days open (not pregnant) compared to herds not utilizing this technology. Finally, in July 2009 a research report from USDA Animal Improvement Programs Laboratory was published using national DHIA data and documented trends in various reproductive parameters using A.I. services from 1996 to 2006.

Table 1* summarizes some of the important trends. It must be noted this data was obtained from the national DHIA database.

Considering the fact that about 50 percent of the U.S. dairy cows are enrolled in DHIA and that this data is the average for DHIA, it can be assumed the reproductive performance for the entire dairy industry is lower than what is illustrated in the table. The most notable trend was the decrease in days to first service. This is probably due to the increased use of timed insemination programs, as documented in several surveys of dairy management practices.

First service and overall conception rates decreased to the lowest values in 2001, but the trend since then shows improvement. The 18-day increase in breeding interval and 11 more days to last breeding during this 11-year period are disturbing. Breeding interval is the number of days between first and last breeding. However, the average interval between consecutive services is an important indicator of post-breeding heat detection rate.

This parameter was not summarized for each year in the study listed above. Post-breeding heat detection reflects the effectiveness of the management team in identifying cows that failed to conceive to the previous service so they can be re-inseminated in a timely manner.

To determine the trend in the average interval between consecutive services for 1996 and 2006, I used the following formula: Average breeding interval = breeding interval between 1st and last service ÷ (number of breedings per cow - 1). The reason number of breedings per cow - 1 is used in this equation is because the first service began the breeding interval and should not be counted as a service within the breeding interval. This calculation accounts for the increased number of breedings or the three-point decrease in overall conception rate between 1996 and 2006.

Using this general estimate of average interval between services (breedings), the averages for 1996 and 2006 were 46.4 and 46.0, respectively. No improvement!

This is where the opportunity exists to improve reproductive performance as measured by days to last breeding, calving interval and 21-day pregnancy rate. Routine and accurate heat detection coupled with early determination of pregnancy status will shorten the interval between services. The goal for this index should be less than 40 days between services.

Several tools are available to reduce the interval to pregnancy diagnosis so resynchronization and timed insemination of open cows can occur on a routine, timely basis. In some herds, more timely palpation for pregnancy is warranted. This may require more frequent visits by the veterinarian so cows that failed to conceive are identified earlier and can be rebred sooner. The use of ultrasound or blood testing to determine pregnancy, are tools that are also being used to determine pregnancy status on a timelier basis so a resynchronization program can be implemented. PD

*References and tables omitted but are available upon request at editor@progressivedairy.com.

—Excerpts from Penn State Dairy Digest, August 2008
Michael O’Connor
Dairy Science
Penn State
moconnor@psu.edu