Improving Submission Rates for Insemination Following Summer Heat Stress

Posted: August 6, 2005

The heat and humidity this summer has severely affected reproductive performance. Lower pregnancy rates should be expected because of higher rate of fertilization failure and embryonic death.

It has been estimated that a rise in uterine temperature by only 1° F causes a 10-15% decrease in conception rate. Irregular intervals between heats may also be noticed. Furthermore, during heat stress blood flow to the placenta is reduced. Research from Florida showed that heat stress during the last trimester of pregnancy effected placental development and calf weights were reduced. Possibly the reduced blood flow to the placenta may be responsible for more abortions during this period of heat stress.

For those dairy producers who do not use an estrous synchronization program or timed breeding program should consider implementing such a program when temperatures subside in late summer and early fall. The objective of these programs is to increase the submission rate for insemination in a timely manner. The second important step to reducing the interservice interval is to intensely observe for heat 18-24 days following the initial timed insemination. Finally, consider implementing a Resynchronization program to efficiently manage open cows so fewer days are lost before rebreeding. There are several Resynch programs available. The basic program involves initiating the Ovsynch program by administering gonadotropin releasing hormone (GnRH) seven days prior to scheduled pregnancy exam day to all cows not detected in heat after first service. Those cows diagnosed not pregnant receive prostaglandin (PG) that day followed by another GnRH injection 48 hours later and they are time inseminated 10 – 18 hours after second GnRH. This system significantly reduces interval to reinsemination. Even though pregnant cows receive a GnRH injection, recent research has shown this does not cause embryonic mortality.

One Resynch program involves injecting GnRH on Day 33 post-insemination followed by pregnancy examination on Day 40. Cows diagnosed not pregnant that day would receive PG and two days later receive GnRH. The timed insemination would occur 10-18 hours later. There are some important factors to consider when implementing these programs.

  1. Observe cows for heat 19-24 days after initial timed insemination.
  2. Pregnancy examinations must be timely and accurate.
  3. An accurate and current record system must be established so palpations and hormonal injections follow the prescribed schedule and pregnant cows are not mistakenly injected with PG. Don’t take shortcuts.
  4. Synchronization and resynchronization programs reduce or concentrate time spent detecting heats but these programs do not completely eliminate heat detection. Remember that many cows that don’t conceive maintain a certain degree of synchrony following the initial synchronization. This group should be watched intensely for heat 18 –24 days later. This time period presents a great opportunity to identify open cows and submit them for rebreeding. Considerable time is saved.
  5. All employees working with the cattle should understand the protocol.
  6. Discuss these concepts with your veterinarian and AI technician. Develop a plan that works in your management system.

Michael O’Connor, Dairy and Animal Science Extension