Fertility is influenced by many factors, and one of the best methods to look at the factors is with the “Equation of Reproduction”. The Equation of Reproduction includes the following 4 areas:
- Percentage of animals detected in standing estrus and inseminated
- Inseminator efficiency
- Fertility level of the semen
- Fertility level of the herd.
Each of the preceding areas will be discussed in this series. Part l of the four-part series, “Managing for Reproductive Success”, discussed the limiting aspects of improper estrus detection: 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”.
Flushing embryos following insemination has reported that fertilization rates following natural service or artificial insemination (AI) in cattle range from 89 to 100%. 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. A detailed inventory of semen should be 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. 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.
Using conventional semen, many studies have compared site of deposition on pregnancy success. 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. 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. Unfortunately, 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. Studies have reported cervical insemination errors account for approximately 20% of attempted uterine body depositions, and cervical insemination resulted in at least a 10% decrease in fertility when compared with deposition of semen in the uterine body. Clearly, all AI technicians must develop sufficient skill to recognize when the tip of the AI gun remains in the cervix. 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.
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: 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, and c) the effect of elapsed time from initiation of thawing straws of semen to seminal deposition on conception rates. Average conception rate differed between PAI and HI (45% vs. 27%, respectively), but 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. Nevertheless, a general recommendation as to the number of straws that should be thawed simultaneously detracts from the overall importance of proper semen handling for successful AI. 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, and e) deposit semen in the uterus of the cow within approximately 15 minutes after thawing.
With natural service inseminator efficiency is influenced by the ability of a bull to service a cow. The purpose of the physical examination portion of a breeding soundness evaluation is to determine a bull's mating ability. Mating ability can be described as the physical capabilities needed to successfully breed a cow. In addition to structural unsoundness, diseases or injuries to the penis or prepuce can result in an inability to breed via natural service. These abnormalities will only be detected by careful examination or observing an attempted mating of a cow. A bull that has high quality semen but is unable to physically breed cows is unsatisfactory for natural service. Most producers recognize physical problems that will inhibit a bull from successfully breeding a cow; however, research from Canada has reported that almost 4% of bulls taken to have a breeding soundness exam and had semen quality sufficient to pass a breeding soundness examination could not physically breed a cow.
For more information on beef reproduction please visit iGrow or one of your regional field or state extension specialists.
Article written with contributions from George Perry.