Current Progressive Dairy digital edition

0709PD: Comparing natural service to artificial insemination

Michael O’Connor Published on 24 April 2009

Achieving a high, accurate heat-detection rate (HDR) is a major challenge to dairy producers. There are management issues affecting HDR such as labor constraints, commitment to effective heat detection and inaccurate submission of cows for insemination. Furthermore there is good evidence that cow factors and environmental conditions significantly contribute to a reduction in the expression of estrus.

When herd managers cannot maintain an effective visual heat detection program, they have several options to improve submission rates for breeding. These include implementing an estrous synchronization/timed insemination program, routine use of heat detection aids, contracting heat detection to artificial insemination personnel or resorting to use of natural service.



A survey of 103 large herds with an average herd size of 613 cows across the U.S. revealed that approximately 90 percent of the herds used synchronization/timed A.I. programs and a majority also used heat detection aids. A recent report from USDA documented that the average days to first service in the U.S. has decreased six days between 2001 and 2005. This may be indirect evidence that timed A.I. programs are improving submission rates to insemination. Furthermore, research published in the Journal of Dairy Science reported that herds using synchronization programs have 17 fewer days open.

Data presented at the Dairy Cattle Reproduction Council annual conference provided data from a direct comparison of a timed A.I. (TAI) program with natural service (NS) in a large herd. Beginning at 42±3 days cows in the TAI group were assigned to a Presynch – Ovsynch 56 program. Eighteen days following insemination a CIDR was inserted and GnRH was injected seven days later (25 days after original TAI).

Cows diagnosed not pregnant by ultrasound at 32 days were administered prostaglandin (PG), followed by GnRH at 56 hours and inseminated 16 hours later (resynchronization). Pregnant cows were reexamined by rectal palpation at 60 days.

Cows in the NS group received PG at 42±3 and 56±3 days and moved to pens with bulls at 70 days. The bull- to-cow ratio was 1 to 20 and bulls were rested for 14 days after a 14-day exposure to cows. Bulls also received a breeding soundness examination. Ultrasound at 42 days was used to determine pregnancy status in this group.

Preliminary results during the cooler months in Florida (December 2006 to May 2007) are as follows. The median time when 50 percent of the cows were pregnant in either group was 104 and 103 days for TAI and NS, respectively. There was no significant difference between groups.


However, there was a significant difference in pregnancy rate for first service through 91 days postpartum, as 25 percent of all pregnant cows conceived 11 days earlier in the TAI group. Pregnancy losses estimated over four services were 14.9 percent and 11.8 percent for TAI and NS groups, respectively.

The researchers noted that when compared to the NS group, more cows in the TAI group were submitted for insemination during a narrow window of time. Furthermore, the pregnancy rates of 45.9 percent to first service and 32.7 percent to resynchronization at second service indicate a very good response to TAI.

In summary, this is another controlled study showing no significant advantage to NS. When the direct and indirect expenses of NS are considered, there is a cost and risk associated with NS. It is the responsibility of the dairy producer to provide a safe working environment for employees and family. PD

References omitted but are available upon request at

—Excerpts from Penn State Dairy Digest, October 2008

Michael O’Connor
Dairy Extension
Penn State