Opportunity for Improvement in Reproductive Performance

Posted: August 12, 2009

The opportunity exists to improve reproductive performance as measured by days to last breeding, calving interval, and 21-day pregnancy rate.

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 continued “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. 2006, reported that 87% of the herds used estrous synchronization or timed AI programs. Furthermore it was documented by Goodling (2005) 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 (Norman et. al. 2009) was published using national DHIA data and documented trends in various reproductive parameters using AI 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 data base. Considering the fact that about 50% of the US dairy cows are enrolled in DHIA and 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.

Table 1. Average values (DHIA) for reproductive traits for US Holsteins from 1996 and 2006. (Norman 2009. JDS 92:3517). Only AI services were included.

Breeding year Days to 1st breeding Conception 1st service (%) Conception all services (%) Number services Breeding interval (days)1 Days to last breeding2 Calving interval (days)
1996 92 34 33 2.1 51 133 410
1997 94 33 32 2.1 53 136 416
1998 94 32 30 2.1 58 140 422
1999 94 30 29 2.2 59 142 428
2000 91 30 28 2.2 59 140 426
2001 90 27 26 2.3 60 142 428
2002 90 30 29 2.3 64 145 426
2003 90 32 30 2.4 68 147 425
2004 87 33 31 2.5 67 143 422
2005 86 31 29 2.6 71 146 423
2006 86 31 30 2.5 69 144 422

1Breeding interval - number of days between first and last breeding. 2Days to last breeding – days between calving and last breeding.

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 eleven 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 rebred sooner. The use of ultrasound or BioPRYN®, blood test for the protein associated with pregnancy, are tools that are also being used to determine pregnancy status on a timelier basis so a resynchronization program can be implemented.

Michael O’Connor,  Dairy and Animal Science Extension