Cows not detected in estrus have no opportunity to conceive. In artificial insemination systems, that opportunity to conceive when a cow is detected in estrus also depends on another limiting factor, "Inseminator Efficiency," Perry says.
Based on research, Perry says that fertilization rates don’t differ between animals following natural service or artificial insemination (AI).
He points to a study which flushed embryos following insemination. The data showed that fertilization rates following natural service or artificial insemination (AI) in cattle range from 89 to 100 percent. Furthermore, when pregnancy rates from 13,942 first service artificial inseminations were compared to 6,310 first services by natural service, no difference was detected between artificial insemination and natural service.
"With AI, inseminator efficiency is influenced by semen handling and the ability of the technician to deposit semen in the correct location," Perry said.
To improve semen handling, he encourages cattle producers to have a detailed inventory of semen easily accessible, so that straws may be located and removed from the tank quickly to avoid exposure of semen to ambient temperature.
"When removing a straw from a liquid nitrogen refrigerator, it is imperative that the technician keep the canister, cane and unused semen straws as low as possible in the neck of the tank," Perry said.
He adds that it is best to keep all unused straws below the frost-line in the neck of the tank. The temperature of liquid nitrogen in a semen tank is -196 degrees Celsius (C) (-326 degrees Fahrenheit, (F)). Sperm injury (as judged by sperm motility) occurs at temperatures as warm as -79 C (-110 F), and injury to sperm cannot be corrected by returning semen to the liquid nitrogen.
Site of Deposition
Many studies have compared site of deposition on pregnancy success, says Perry.
"Some studies have reported increased conception rates when semen was deposited in the uterine horns rather than the uterine body, but other studies have reported no difference in fertility when comparing uterine body and uterine horn inseminations," he said. "Furthermore, an inseminator and site of semen deposition interaction has been reported, with evidence of either an increase, decrease, or no effect of uterine horn deposition on conception rate for individual inseminators."
Perry says it is not clear why some studies have shown an advantage following uterine horn insemination while others have not.
"A possible explanation for the positive effect of uterine horn inseminations may be related to the minimization or elimination of cervical semen deposition," he said. "Studies have reported cervical insemination errors account for approximately 20 percent of attempted uterine body depositions, and cervical insemination resulted in at least a 10 percent decrease in fertility when compared with deposition of semen in the uterine body."
Based on this information, Perry says in order to maximize conception rates, AI technicians must continue to manipulate the reproductive tract until the tip of the AI gun is past the cervix and deposition into the uterus can be accomplished.
"Clearly, all AI technicians must develop sufficient skill to recognize when the tip of the AI gun remains in the cervix," he said.
When numerous cows must be inseminated on a given day, multiple straws of semen are routinely thawed simultaneously to facilitate AI.
Research from the University of Idaho determined simultaneous thawing and sequence of insemination (1st, 2nd, 3rd or 4th), and elapsed time from initial thaw to completion of fourth AI had no effect on conception rate within inseminator group; however average conception rate differed between groups which were treated by a professional AI technician and those serviced by a herdsman-inseminator (45% vs. 27%, respectively).
The researched looked at the following:
a) The effect of simultaneous thawing of multiple 0.5-mL straws of semen and sequence of insemination (1st, 2nd, 3rd or 4th) on conception rates;
b) Whether conception rates achieved following AI by professional AI technicians (PAI) and herdsman-inseminators (HI) differed;
c) The effect of elapsed time from initiation of thawing straws of semen to seminal deposition on conception rates.
Perry says this research reinforces the important role handling plays in conception.
He adds that conception rates are most likely maximized when personnel:
a) Follow proper procedures for thawing semen;
b) Prevent direct straw-to-straw contact during thawing of multiple straws; simultaneously to avoid decreased post-thaw sperm viability as a result of straws sticking together;
c) Use appropriate hygienic procedures;
d) Maintain thermal protection of straws during AI gun assembly and transport to the cow;
e) Deposit semen in the uterus of the cow within approximately 15 minutes after thawing.
For more information related to detecting standing estrus contact, Jim Krantz, SDSU Extension Cow/Calf Field Specialist at [email protected] or 605-995-7381 or Dr. George Perry, SDSU Extension Beef Reproductive Management Specialist at [email protected] or 605-688-5456. To listen to a recent iGrow Radio Network interview on this topic with Dr. George Perry, and to review all four articles in this four-part series released by SDSU Extension visit iGrow.org.
Part 2 of a four-part series
Fertility is influenced by many factors, and one of the best methods to look at factors that influence fertility is with the ‘Equation of Reproduction,’ says George Perry, SDSU Extension Beef Reproductive Management Specialist.
Perry explains that the ‘Equation of Reproduction’ includes the following four areas:
Percentage of animals detected in standing estrus and inseminated;
Fertility level of the semen and;
Fertility level of the herd.
Each of the areas will be discussed in the four-part series on managing for reproductive success by SDSU Extension.